usb: gadget: ffs: Execute copy_to_user() with USER_DS set

[mirror_ubuntu-bionic-kernel.git] / drivers / usb / gadget / function / f_fs.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * f_fs.c -- user mode file system API for USB composite function controllers
 *
 * Copyright (C) 2010 Samsung Electronics
 * Author: Michal Nazarewicz <mina86@mina86.com>
 *
 * Based on inode.c (GadgetFS) which was:
 * Copyright (C) 2003-2004 David Brownell
 * Copyright (C) 2003 Agilent Technologies
 */


/* #define DEBUG */
/* #define VERBOSE_DEBUG */

#include <linux/blkdev.h>
#include <linux/pagemap.h>
#include <linux/export.h>
#include <linux/hid.h>
#include <linux/module.h>
#include <linux/sched/signal.h>
#include <linux/uio.h>
#include <asm/unaligned.h>

#include <linux/usb/composite.h>
#include <linux/usb/functionfs.h>

#include <linux/aio.h>
#include <linux/mmu_context.h>
#include <linux/poll.h>
#include <linux/eventfd.h>

#include "u_fs.h"
#include "u_f.h"
#include "u_os_desc.h"
#include "configfs.h"

#define FUNCTIONFS_MAGIC        0xa647361 /* Chosen by a honest dice roll ;) */

/* Reference counter handling */
static void ffs_data_get(struct ffs_data *ffs);
static void ffs_data_put(struct ffs_data *ffs);
/* Creates new ffs_data object. */
static struct ffs_data *__must_check ffs_data_new(const char *dev_name)
        __attribute__((malloc));

/* Opened counter handling. */
static void ffs_data_opened(struct ffs_data *ffs);
static void ffs_data_closed(struct ffs_data *ffs);

/* Called with ffs->mutex held; take over ownership of data. */
static int __must_check
__ffs_data_got_descs(struct ffs_data *ffs, char *data, size_t len);
static int __must_check
__ffs_data_got_strings(struct ffs_data *ffs, char *data, size_t len);


/* The function structure ***************************************************/

struct ffs_ep;

struct ffs_function {
        struct usb_configuration        *conf;
        struct usb_gadget               *gadget;
        struct ffs_data                 *ffs;

        struct ffs_ep                   *eps;
        u8                              eps_revmap[16];
        short                           *interfaces_nums;

        struct usb_function             function;
};


static struct ffs_function *ffs_func_from_usb(struct usb_function *f)
{
        return container_of(f, struct ffs_function, function);
}


static inline enum ffs_setup_state
ffs_setup_state_clear_cancelled(struct ffs_data *ffs)
{
        return (enum ffs_setup_state)
                cmpxchg(&ffs->setup_state, FFS_SETUP_CANCELLED, FFS_NO_SETUP);
}


static void ffs_func_eps_disable(struct ffs_function *func);
static int __must_check ffs_func_eps_enable(struct ffs_function *func);

static int ffs_func_bind(struct usb_configuration *,
                         struct usb_function *);
static int ffs_func_set_alt(struct usb_function *, unsigned, unsigned);
static void ffs_func_disable(struct usb_function *);
static int ffs_func_setup(struct usb_function *,
                          const struct usb_ctrlrequest *);
static bool ffs_func_req_match(struct usb_function *,
                               const struct usb_ctrlrequest *,
                               bool config0);
static void ffs_func_suspend(struct usb_function *);
static void ffs_func_resume(struct usb_function *);


static int ffs_func_revmap_ep(struct ffs_function *func, u8 num);
static int ffs_func_revmap_intf(struct ffs_function *func, u8 intf);


/* The endpoints structures *************************************************/

struct ffs_ep {
        struct usb_ep                   *ep;    /* P: ffs->eps_lock */
        struct usb_request              *req;   /* P: epfile->mutex */

        /* [0]: full speed, [1]: high speed, [2]: super speed */
        struct usb_endpoint_descriptor  *descs[3];

        u8                              num;

        int                             status; /* P: epfile->mutex */
};

struct ffs_epfile {
        /* Protects ep->ep and ep->req. */
        struct mutex                    mutex;

        struct ffs_data                 *ffs;
        struct ffs_ep                   *ep;    /* P: ffs->eps_lock */

        struct dentry                   *dentry;

        /*
         * Buffer for holding data from partial reads which may happen since
         * we’re rounding user read requests to a multiple of a max packet size.
         *
         * The pointer is initialised with NULL value and may be set by
         * __ffs_epfile_read_data function to point to a temporary buffer.
         *
         * In normal operation, calls to __ffs_epfile_read_buffered will consume
         * data from said buffer and eventually free it.  Importantly, while the
         * function is using the buffer, it sets the pointer to NULL.  This is
         * all right since __ffs_epfile_read_data and __ffs_epfile_read_buffered
         * can never run concurrently (they are synchronised by epfile->mutex)
         * so the latter will not assign a new value to the pointer.
         *
         * Meanwhile ffs_func_eps_disable frees the buffer (if the pointer is
         * valid) and sets the pointer to READ_BUFFER_DROP value.  This special
         * value is crux of the synchronisation between ffs_func_eps_disable and
         * __ffs_epfile_read_data.
         *
         * Once __ffs_epfile_read_data is about to finish it will try to set the
         * pointer back to its old value (as described above), but seeing as the
         * pointer is not-NULL (namely READ_BUFFER_DROP) it will instead free
         * the buffer.
         *
         * == State transitions ==
         *
         * • ptr == NULL:  (initial state)
         *   ◦ __ffs_epfile_read_buffer_free: go to ptr == DROP
         *   ◦ __ffs_epfile_read_buffered:    nop
         *   ◦ __ffs_epfile_read_data allocates temp buffer: go to ptr == buf
         *   ◦ reading finishes:              n/a, not in ‘and reading’ state
         * • ptr == DROP:
         *   ◦ __ffs_epfile_read_buffer_free: nop
         *   ◦ __ffs_epfile_read_buffered:    go to ptr == NULL
         *   ◦ __ffs_epfile_read_data allocates temp buffer: free buf, nop
         *   ◦ reading finishes:              n/a, not in ‘and reading’ state
         * • ptr == buf:
         *   ◦ __ffs_epfile_read_buffer_free: free buf, go to ptr == DROP
         *   ◦ __ffs_epfile_read_buffered:    go to ptr == NULL and reading
         *   ◦ __ffs_epfile_read_data:        n/a, __ffs_epfile_read_buffered
         *                                    is always called first
         *   ◦ reading finishes:              n/a, not in ‘and reading’ state
         * • ptr == NULL and reading:
         *   ◦ __ffs_epfile_read_buffer_free: go to ptr == DROP and reading
         *   ◦ __ffs_epfile_read_buffered:    n/a, mutex is held
         *   ◦ __ffs_epfile_read_data:        n/a, mutex is held
         *   ◦ reading finishes and …
         *     … all data read:               free buf, go to ptr == NULL
         *     … otherwise:                   go to ptr == buf and reading
         * • ptr == DROP and reading:
         *   ◦ __ffs_epfile_read_buffer_free: nop
         *   ◦ __ffs_epfile_read_buffered:    n/a, mutex is held
         *   ◦ __ffs_epfile_read_data:        n/a, mutex is held
         *   ◦ reading finishes:              free buf, go to ptr == DROP
         */
        struct ffs_buffer               *read_buffer;
#define READ_BUFFER_DROP ((struct ffs_buffer *)ERR_PTR(-ESHUTDOWN))

        char                            name[5];

        unsigned char                   in;     /* P: ffs->eps_lock */
        unsigned char                   isoc;   /* P: ffs->eps_lock */

        unsigned char                   _pad;
};

struct ffs_buffer {
        size_t length;
        char *data;
        char storage[];
};

/*  ffs_io_data structure ***************************************************/

struct ffs_io_data {
        bool aio;
        bool read;

        struct kiocb *kiocb;
        struct iov_iter data;
        const void *to_free;
        char *buf;

        struct mm_struct *mm;
        struct work_struct work;

        struct usb_ep *ep;
        struct usb_request *req;

        struct ffs_data *ffs;
};

struct ffs_desc_helper {
        struct ffs_data *ffs;
        unsigned interfaces_count;
        unsigned eps_count;
};

static int  __must_check ffs_epfiles_create(struct ffs_data *ffs);
static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count);

static struct dentry *
ffs_sb_create_file(struct super_block *sb, const char *name, void *data,
                   const struct file_operations *fops);

/* Devices management *******************************************************/

DEFINE_MUTEX(ffs_lock);
EXPORT_SYMBOL_GPL(ffs_lock);

static struct ffs_dev *_ffs_find_dev(const char *name);
static struct ffs_dev *_ffs_alloc_dev(void);
static void _ffs_free_dev(struct ffs_dev *dev);
static void *ffs_acquire_dev(const char *dev_name);
static void ffs_release_dev(struct ffs_data *ffs_data);
static int ffs_ready(struct ffs_data *ffs);
static void ffs_closed(struct ffs_data *ffs);

/* Misc helper functions ****************************************************/

static int ffs_mutex_lock(struct mutex *mutex, unsigned nonblock)
        __attribute__((warn_unused_result, nonnull));
static char *ffs_prepare_buffer(const char __user *buf, size_t len)
        __attribute__((warn_unused_result, nonnull));


/* Control file aka ep0 *****************************************************/

static void ffs_ep0_complete(struct usb_ep *ep, struct usb_request *req)
{
        struct ffs_data *ffs = req->context;

        complete(&ffs->ep0req_completion);
}

static int __ffs_ep0_queue_wait(struct ffs_data *ffs, char *data, size_t len)
{
        struct usb_request *req = ffs->ep0req;
        int ret;

        req->zero     = len < le16_to_cpu(ffs->ev.setup.wLength);

        spin_unlock_irq(&ffs->ev.waitq.lock);

        req->buf      = data;
        req->length   = len;

        /*
         * UDC layer requires to provide a buffer even for ZLP, but should
         * not use it at all. Let's provide some poisoned pointer to catch
         * possible bug in the driver.
         */
        if (req->buf == NULL)
                req->buf = (void *)0xDEADBABE;

        reinit_completion(&ffs->ep0req_completion);

        ret = usb_ep_queue(ffs->gadget->ep0, req, GFP_ATOMIC);
        if (unlikely(ret < 0))
                return ret;

        ret = wait_for_completion_interruptible(&ffs->ep0req_completion);
        if (unlikely(ret)) {
                usb_ep_dequeue(ffs->gadget->ep0, req);
                return -EINTR;
        }

        ffs->setup_state = FFS_NO_SETUP;
        return req->status ? req->status : req->actual;
}

static int __ffs_ep0_stall(struct ffs_data *ffs)
{
        if (ffs->ev.can_stall) {
                pr_vdebug("ep0 stall\n");
                usb_ep_set_halt(ffs->gadget->ep0);
                ffs->setup_state = FFS_NO_SETUP;
                return -EL2HLT;
        } else {
                pr_debug("bogus ep0 stall!\n");
                return -ESRCH;
        }
}

static ssize_t ffs_ep0_write(struct file *file, const char __user *buf,
                             size_t len, loff_t *ptr)
{
        struct ffs_data *ffs = file->private_data;
        ssize_t ret;
        char *data;

        ENTER();

        /* Fast check if setup was canceled */
        if (ffs_setup_state_clear_cancelled(ffs) == FFS_SETUP_CANCELLED)
                return -EIDRM;

        /* Acquire mutex */
        ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
        if (unlikely(ret < 0))
                return ret;

        /* Check state */
        switch (ffs->state) {
        case FFS_READ_DESCRIPTORS:
        case FFS_READ_STRINGS:
                /* Copy data */
                if (unlikely(len < 16)) {
                        ret = -EINVAL;
                        break;
                }

                data = ffs_prepare_buffer(buf, len);
                if (IS_ERR(data)) {
                        ret = PTR_ERR(data);
                        break;
                }

                /* Handle data */
                if (ffs->state == FFS_READ_DESCRIPTORS) {
                        pr_info("read descriptors\n");
                        ret = __ffs_data_got_descs(ffs, data, len);
                        if (unlikely(ret < 0))
                                break;

                        ffs->state = FFS_READ_STRINGS;
                        ret = len;
                } else {
                        pr_info("read strings\n");
                        ret = __ffs_data_got_strings(ffs, data, len);
                        if (unlikely(ret < 0))
                                break;

                        ret = ffs_epfiles_create(ffs);
                        if (unlikely(ret)) {
                                ffs->state = FFS_CLOSING;
                                break;
                        }

                        ffs->state = FFS_ACTIVE;
                        mutex_unlock(&ffs->mutex);

                        ret = ffs_ready(ffs);
                        if (unlikely(ret < 0)) {
                                ffs->state = FFS_CLOSING;
                                return ret;
                        }

                        return len;
                }
                break;

        case FFS_ACTIVE:
                data = NULL;
                /*
                 * We're called from user space, we can use _irq
                 * rather then _irqsave
                 */
                spin_lock_irq(&ffs->ev.waitq.lock);
                switch (ffs_setup_state_clear_cancelled(ffs)) {
                case FFS_SETUP_CANCELLED:
                        ret = -EIDRM;
                        goto done_spin;

                case FFS_NO_SETUP:
                        ret = -ESRCH;
                        goto done_spin;

                case FFS_SETUP_PENDING:
                        break;
                }

                /* FFS_SETUP_PENDING */
                if (!(ffs->ev.setup.bRequestType & USB_DIR_IN)) {
                        spin_unlock_irq(&ffs->ev.waitq.lock);
                        ret = __ffs_ep0_stall(ffs);
                        break;
                }

                /* FFS_SETUP_PENDING and not stall */
                len = min(len, (size_t)le16_to_cpu(ffs->ev.setup.wLength));

                spin_unlock_irq(&ffs->ev.waitq.lock);

                data = ffs_prepare_buffer(buf, len);
                if (IS_ERR(data)) {
                        ret = PTR_ERR(data);
                        break;
                }

                spin_lock_irq(&ffs->ev.waitq.lock);

                /*
                 * We are guaranteed to be still in FFS_ACTIVE state
                 * but the state of setup could have changed from
                 * FFS_SETUP_PENDING to FFS_SETUP_CANCELLED so we need
                 * to check for that.  If that happened we copied data
                 * from user space in vain but it's unlikely.
                 *
                 * For sure we are not in FFS_NO_SETUP since this is
                 * the only place FFS_SETUP_PENDING -> FFS_NO_SETUP
                 * transition can be performed and it's protected by
                 * mutex.
                 */
                if (ffs_setup_state_clear_cancelled(ffs) ==
                    FFS_SETUP_CANCELLED) {
                        ret = -EIDRM;
done_spin:
                        spin_unlock_irq(&ffs->ev.waitq.lock);
                } else {
                        /* unlocks spinlock */
                        ret = __ffs_ep0_queue_wait(ffs, data, len);
                }
                kfree(data);
                break;

        default:
                ret = -EBADFD;
                break;
        }

        mutex_unlock(&ffs->mutex);
        return ret;
}

/* Called with ffs->ev.waitq.lock and ffs->mutex held, both released on exit. */
static ssize_t __ffs_ep0_read_events(struct ffs_data *ffs, char __user *buf,
                                     size_t n)
{
        /*
         * n cannot be bigger than ffs->ev.count, which cannot be bigger than
         * size of ffs->ev.types array (which is four) so that's how much space
         * we reserve.
         */
        struct usb_functionfs_event events[ARRAY_SIZE(ffs->ev.types)];
        const size_t size = n * sizeof *events;
        unsigned i = 0;

        memset(events, 0, size);

        do {
                events[i].type = ffs->ev.types[i];
                if (events[i].type == FUNCTIONFS_SETUP) {
                        events[i].u.setup = ffs->ev.setup;
                        ffs->setup_state = FFS_SETUP_PENDING;
                }
        } while (++i < n);

        ffs->ev.count -= n;
        if (ffs->ev.count)
                memmove(ffs->ev.types, ffs->ev.types + n,
                        ffs->ev.count * sizeof *ffs->ev.types);

        spin_unlock_irq(&ffs->ev.waitq.lock);
        mutex_unlock(&ffs->mutex);

        return unlikely(copy_to_user(buf, events, size)) ? -EFAULT : size;
}

static ssize_t ffs_ep0_read(struct file *file, char __user *buf,
                            size_t len, loff_t *ptr)
{
        struct ffs_data *ffs = file->private_data;
        char *data = NULL;
        size_t n;
        int ret;

        ENTER();

        /* Fast check if setup was canceled */
        if (ffs_setup_state_clear_cancelled(ffs) == FFS_SETUP_CANCELLED)
                return -EIDRM;

        /* Acquire mutex */
        ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
        if (unlikely(ret < 0))
                return ret;

        /* Check state */
        if (ffs->state != FFS_ACTIVE) {
                ret = -EBADFD;
                goto done_mutex;
        }

        /*
         * We're called from user space, we can use _irq rather then
         * _irqsave
         */
        spin_lock_irq(&ffs->ev.waitq.lock);

        switch (ffs_setup_state_clear_cancelled(ffs)) {
        case FFS_SETUP_CANCELLED:
                ret = -EIDRM;
                break;

        case FFS_NO_SETUP:
                n = len / sizeof(struct usb_functionfs_event);
                if (unlikely(!n)) {
                        ret = -EINVAL;
                        break;
                }

                if ((file->f_flags & O_NONBLOCK) && !ffs->ev.count) {
                        ret = -EAGAIN;
                        break;
                }

                if (wait_event_interruptible_exclusive_locked_irq(ffs->ev.waitq,
                                                        ffs->ev.count)) {
                        ret = -EINTR;
                        break;
                }

                return __ffs_ep0_read_events(ffs, buf,
                                             min(n, (size_t)ffs->ev.count));

        case FFS_SETUP_PENDING:
                if (ffs->ev.setup.bRequestType & USB_DIR_IN) {
                        spin_unlock_irq(&ffs->ev.waitq.lock);
                        ret = __ffs_ep0_stall(ffs);
                        goto done_mutex;
                }

                len = min(len, (size_t)le16_to_cpu(ffs->ev.setup.wLength));

                spin_unlock_irq(&ffs->ev.waitq.lock);

                if (likely(len)) {
                        data = kmalloc(len, GFP_KERNEL);
                        if (unlikely(!data)) {
                                ret = -ENOMEM;
                                goto done_mutex;
                        }
                }

                spin_lock_irq(&ffs->ev.waitq.lock);

                /* See ffs_ep0_write() */
                if (ffs_setup_state_clear_cancelled(ffs) ==
                    FFS_SETUP_CANCELLED) {
                        ret = -EIDRM;
                        break;
                }

                /* unlocks spinlock */
                ret = __ffs_ep0_queue_wait(ffs, data, len);
                if (likely(ret > 0) && unlikely(copy_to_user(buf, data, len)))
                        ret = -EFAULT;
                goto done_mutex;

        default:
                ret = -EBADFD;
                break;
        }

        spin_unlock_irq(&ffs->ev.waitq.lock);
done_mutex:
        mutex_unlock(&ffs->mutex);
        kfree(data);
        return ret;
}

static int ffs_ep0_open(struct inode *inode, struct file *file)
{
        struct ffs_data *ffs = inode->i_private;

        ENTER();

        if (unlikely(ffs->state == FFS_CLOSING))
                return -EBUSY;

        file->private_data = ffs;
        ffs_data_opened(ffs);

        return 0;
}

static int ffs_ep0_release(struct inode *inode, struct file *file)
{
        struct ffs_data *ffs = file->private_data;

        ENTER();

        ffs_data_closed(ffs);

        return 0;
}

static long ffs_ep0_ioctl(struct file *file, unsigned code, unsigned long value)
{
        struct ffs_data *ffs = file->private_data;
        struct usb_gadget *gadget = ffs->gadget;
        long ret;

        ENTER();

        if (code == FUNCTIONFS_INTERFACE_REVMAP) {
                struct ffs_function *func = ffs->func;
                ret = func ? ffs_func_revmap_intf(func, value) : -ENODEV;
        } else if (gadget && gadget->ops->ioctl) {
                ret = gadget->ops->ioctl(gadget, code, value);
        } else {
                ret = -ENOTTY;
        }

        return ret;
}

static unsigned int ffs_ep0_poll(struct file *file, poll_table *wait)
{
        struct ffs_data *ffs = file->private_data;
        unsigned int mask = POLLWRNORM;
        int ret;

        poll_wait(file, &ffs->ev.waitq, wait);

        ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
        if (unlikely(ret < 0))
                return mask;

        switch (ffs->state) {
        case FFS_READ_DESCRIPTORS:
        case FFS_READ_STRINGS:
                mask |= POLLOUT;
                break;

        case FFS_ACTIVE:
                switch (ffs->setup_state) {
                case FFS_NO_SETUP:
                        if (ffs->ev.count)
                                mask |= POLLIN;
                        break;

                case FFS_SETUP_PENDING:
                case FFS_SETUP_CANCELLED:
                        mask |= (POLLIN | POLLOUT);
                        break;
                }
        case FFS_CLOSING:
                break;
        case FFS_DEACTIVATED:
                break;
        }

        mutex_unlock(&ffs->mutex);

        return mask;
}

static const struct file_operations ffs_ep0_operations = {
        .llseek =       no_llseek,

        .open =         ffs_ep0_open,
        .write =        ffs_ep0_write,
        .read =         ffs_ep0_read,
        .release =      ffs_ep0_release,
        .unlocked_ioctl =       ffs_ep0_ioctl,
        .poll =         ffs_ep0_poll,
};


/* "Normal" endpoints operations ********************************************/

static void ffs_epfile_io_complete(struct usb_ep *_ep, struct usb_request *req)
{
        ENTER();
        if (likely(req->context)) {
                struct ffs_ep *ep = _ep->driver_data;
                ep->status = req->status ? req->status : req->actual;
                complete(req->context);
        }
}

static ssize_t ffs_copy_to_iter(void *data, int data_len, struct iov_iter *iter)
{
        ssize_t ret = copy_to_iter(data, data_len, iter);
        if (likely(ret == data_len))
                return ret;

        if (unlikely(iov_iter_count(iter)))
                return -EFAULT;

        /*
         * Dear user space developer!
         *
         * TL;DR: To stop getting below error message in your kernel log, change
         * user space code using functionfs to align read buffers to a max
         * packet size.
         *
         * Some UDCs (e.g. dwc3) require request sizes to be a multiple of a max
         * packet size.  When unaligned buffer is passed to functionfs, it
         * internally uses a larger, aligned buffer so that such UDCs are happy.
         *
         * Unfortunately, this means that host may send more data than was
         * requested in read(2) system call.  f_fs doesn’t know what to do with
         * that excess data so it simply drops it.
         *
         * Was the buffer aligned in the first place, no such problem would
         * happen.
         *
         * Data may be dropped only in AIO reads.  Synchronous reads are handled
         * by splitting a request into multiple parts.  This splitting may still
         * be a problem though so it’s likely best to align the buffer
         * regardless of it being AIO or not..
         *
         * This only affects OUT endpoints, i.e. reading data with a read(2),
         * aio_read(2) etc. system calls.  Writing data to an IN endpoint is not
         * affected.
         */
        pr_err("functionfs read size %d > requested size %zd, dropping excess data. "
               "Align read buffer size to max packet size to avoid the problem.\n",
               data_len, ret);

        return ret;
}

static void ffs_user_copy_worker(struct work_struct *work)
{
        struct ffs_io_data *io_data = container_of(work, struct ffs_io_data,
                                                   work);
        int ret = io_data->req->status ? io_data->req->status :
                                         io_data->req->actual;
        bool kiocb_has_eventfd = io_data->kiocb->ki_flags & IOCB_EVENTFD;

        if (io_data->read && ret > 0) {
                mm_segment_t oldfs = get_fs();

                set_fs(USER_DS);
                use_mm(io_data->mm);
                ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
                unuse_mm(io_data->mm);
                set_fs(oldfs);
        }

        io_data->kiocb->ki_complete(io_data->kiocb, ret, ret);

        if (io_data->ffs->ffs_eventfd && !kiocb_has_eventfd)
                eventfd_signal(io_data->ffs->ffs_eventfd, 1);

        usb_ep_free_request(io_data->ep, io_data->req);

        if (io_data->read)
                kfree(io_data->to_free);
        kfree(io_data->buf);
        kfree(io_data);
}

static void ffs_epfile_async_io_complete(struct usb_ep *_ep,
                                         struct usb_request *req)
{
        struct ffs_io_data *io_data = req->context;
        struct ffs_data *ffs = io_data->ffs;

        ENTER();

        INIT_WORK(&io_data->work, ffs_user_copy_worker);
        queue_work(ffs->io_completion_wq, &io_data->work);
}

static void __ffs_epfile_read_buffer_free(struct ffs_epfile *epfile)
{
        /*
         * See comment in struct ffs_epfile for full read_buffer pointer
         * synchronisation story.
         */
        struct ffs_buffer *buf = xchg(&epfile->read_buffer, READ_BUFFER_DROP);
        if (buf && buf != READ_BUFFER_DROP)
                kfree(buf);
}

/* Assumes epfile->mutex is held. */
static ssize_t __ffs_epfile_read_buffered(struct ffs_epfile *epfile,
                                          struct iov_iter *iter)
{
        /*
         * Null out epfile->read_buffer so ffs_func_eps_disable does not free
         * the buffer while we are using it.  See comment in struct ffs_epfile
         * for full read_buffer pointer synchronisation story.
         */
        struct ffs_buffer *buf = xchg(&epfile->read_buffer, NULL);
        ssize_t ret;
        if (!buf || buf == READ_BUFFER_DROP)
                return 0;

        ret = copy_to_iter(buf->data, buf->length, iter);
        if (buf->length == ret) {
                kfree(buf);
                return ret;
        }

        if (unlikely(iov_iter_count(iter))) {
                ret = -EFAULT;
        } else {
                buf->length -= ret;
                buf->data += ret;
        }

        if (cmpxchg(&epfile->read_buffer, NULL, buf))
                kfree(buf);

        return ret;
}

/* Assumes epfile->mutex is held. */
static ssize_t __ffs_epfile_read_data(struct ffs_epfile *epfile,
                                      void *data, int data_len,
                                      struct iov_iter *iter)
{
        struct ffs_buffer *buf;

        ssize_t ret = copy_to_iter(data, data_len, iter);
        if (likely(data_len == ret))
                return ret;

        if (unlikely(iov_iter_count(iter)))
                return -EFAULT;

        /* See ffs_copy_to_iter for more context. */
        pr_warn("functionfs read size %d > requested size %zd, splitting request into multiple reads.",
                data_len, ret);

        data_len -= ret;
        buf = kmalloc(sizeof(*buf) + data_len, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;
        buf->length = data_len;
        buf->data = buf->storage;
        memcpy(buf->storage, data + ret, data_len);

        /*
         * At this point read_buffer is NULL or READ_BUFFER_DROP (if
         * ffs_func_eps_disable has been called in the meanwhile).  See comment
         * in struct ffs_epfile for full read_buffer pointer synchronisation
         * story.
         */
        if (unlikely(cmpxchg(&epfile->read_buffer, NULL, buf)))
                kfree(buf);

        return ret;
}

static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
{
        struct ffs_epfile *epfile = file->private_data;
        struct usb_request *req;
        struct ffs_ep *ep;
        char *data = NULL;
        ssize_t ret, data_len = -EINVAL;
        int halt;

        /* Are we still active? */
        if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
                return -ENODEV;

        /* Wait for endpoint to be enabled */
        ep = epfile->ep;
        if (!ep) {
                if (file->f_flags & O_NONBLOCK)
                        return -EAGAIN;

                ret = wait_event_interruptible(
                                epfile->ffs->wait, (ep = epfile->ep));
                if (ret)
                        return -EINTR;
        }

        /* Do we halt? */
        halt = (!io_data->read == !epfile->in);
        if (halt && epfile->isoc)
                return -EINVAL;

        /* We will be using request and read_buffer */
        ret = ffs_mutex_lock(&epfile->mutex, file->f_flags & O_NONBLOCK);
        if (unlikely(ret))
                goto error;

        /* Allocate & copy */
        if (!halt) {
                struct usb_gadget *gadget;

                /*
                 * Do we have buffered data from previous partial read?  Check
                 * that for synchronous case only because we do not have
                 * facility to ‘wake up’ a pending asynchronous read and push
                 * buffered data to it which we would need to make things behave
                 * consistently.
                 */
                if (!io_data->aio && io_data->read) {
                        ret = __ffs_epfile_read_buffered(epfile, &io_data->data);
                        if (ret)
                                goto error_mutex;
                }

                /*
                 * if we _do_ wait above, the epfile->ffs->gadget might be NULL
                 * before the waiting completes, so do not assign to 'gadget'
                 * earlier
                 */
                gadget = epfile->ffs->gadget;

                spin_lock_irq(&epfile->ffs->eps_lock);
                /* In the meantime, endpoint got disabled or changed. */
                if (epfile->ep != ep) {
                        ret = -ESHUTDOWN;
                        goto error_lock;
                }
                data_len = iov_iter_count(&io_data->data);
                /*
                 * Controller may require buffer size to be aligned to
                 * maxpacketsize of an out endpoint.
                 */
                if (io_data->read)
                        data_len = usb_ep_align_maybe(gadget, ep->ep, data_len);
                spin_unlock_irq(&epfile->ffs->eps_lock);

                data = kmalloc(data_len, GFP_KERNEL);
                if (unlikely(!data)) {
                        ret = -ENOMEM;
                        goto error_mutex;
                }
                if (!io_data->read &&
                    !copy_from_iter_full(data, data_len, &io_data->data)) {
                        ret = -EFAULT;
                        goto error_mutex;
                }
        }

        spin_lock_irq(&epfile->ffs->eps_lock);

        if (epfile->ep != ep) {
                /* In the meantime, endpoint got disabled or changed. */
                ret = -ESHUTDOWN;
        } else if (halt) {
                ret = usb_ep_set_halt(ep->ep);
                if (!ret)
                        ret = -EBADMSG;
        } else if (unlikely(data_len == -EINVAL)) {
                /*
                 * Sanity Check: even though data_len can't be used
                 * uninitialized at the time I write this comment, some
                 * compilers complain about this situation.
                 * In order to keep the code clean from warnings, data_len is
                 * being initialized to -EINVAL during its declaration, which
                 * means we can't rely on compiler anymore to warn no future
                 * changes won't result in data_len being used uninitialized.
                 * For such reason, we're adding this redundant sanity check
                 * here.
                 */
                WARN(1, "%s: data_len == -EINVAL\n", __func__);
                ret = -EINVAL;
        } else if (!io_data->aio) {
                DECLARE_COMPLETION_ONSTACK(done);
                bool interrupted = false;

                req = ep->req;
                req->buf      = data;
                req->length   = data_len;

                req->context  = &done;
                req->complete = ffs_epfile_io_complete;

                ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);
                if (unlikely(ret < 0))
                        goto error_lock;

                spin_unlock_irq(&epfile->ffs->eps_lock);

                if (unlikely(wait_for_completion_interruptible(&done))) {
                        /*
                         * To avoid race condition with ffs_epfile_io_complete,
                         * dequeue the request first then check
                         * status. usb_ep_dequeue API should guarantee no race
                         * condition with req->complete callback.
                         */
                        usb_ep_dequeue(ep->ep, req);
                        interrupted = ep->status < 0;
                }

                if (interrupted)
                        ret = -EINTR;
                else if (io_data->read && ep->status > 0)
                        ret = __ffs_epfile_read_data(epfile, data, ep->status,
                                                     &io_data->data);
                else
                        ret = ep->status;
                goto error_mutex;
        } else if (!(req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC))) {
                ret = -ENOMEM;
        } else {
                req->buf      = data;
                req->length   = data_len;

                io_data->buf = data;
                io_data->ep = ep->ep;
                io_data->req = req;
                io_data->ffs = epfile->ffs;

                req->context  = io_data;
                req->complete = ffs_epfile_async_io_complete;

                ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);
                if (unlikely(ret)) {
                        usb_ep_free_request(ep->ep, req);
                        goto error_lock;
                }

                ret = -EIOCBQUEUED;
                /*
                 * Do not kfree the buffer in this function.  It will be freed
                 * by ffs_user_copy_worker.
                 */
                data = NULL;
        }

error_lock:
        spin_unlock_irq(&epfile->ffs->eps_lock);
error_mutex:
        mutex_unlock(&epfile->mutex);
error:
        kfree(data);
        return ret;
}

static int
ffs_epfile_open(struct inode *inode, struct file *file)
{
        struct ffs_epfile *epfile = inode->i_private;

        ENTER();

        if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
                return -ENODEV;

        file->private_data = epfile;
        ffs_data_opened(epfile->ffs);

        return 0;
}

static int ffs_aio_cancel(struct kiocb *kiocb)
{
        struct ffs_io_data *io_data = kiocb->private;
        struct ffs_epfile *epfile = kiocb->ki_filp->private_data;
        int value;

        ENTER();

        spin_lock_irq(&epfile->ffs->eps_lock);

        if (likely(io_data && io_data->ep && io_data->req))
                value = usb_ep_dequeue(io_data->ep, io_data->req);
        else
                value = -EINVAL;

        spin_unlock_irq(&epfile->ffs->eps_lock);

        return value;
}

static ssize_t ffs_epfile_write_iter(struct kiocb *kiocb, struct iov_iter *from)
{
        struct ffs_io_data io_data, *p = &io_data;
        ssize_t res;

        ENTER();

        if (!is_sync_kiocb(kiocb)) {
                p = kmalloc(sizeof(io_data), GFP_KERNEL);
                if (unlikely(!p))
                        return -ENOMEM;
                p->aio = true;
        } else {
                p->aio = false;
        }

        p->read = false;
        p->kiocb = kiocb;
        p->data = *from;
        p->mm = current->mm;

        kiocb->private = p;

        if (p->aio)
                kiocb_set_cancel_fn(kiocb, ffs_aio_cancel);

        res = ffs_epfile_io(kiocb->ki_filp, p);
        if (res == -EIOCBQUEUED)
                return res;
        if (p->aio)
                kfree(p);
        else
                *from = p->data;
        return res;
}

static ssize_t ffs_epfile_read_iter(struct kiocb *kiocb, struct iov_iter *to)
{
        struct ffs_io_data io_data, *p = &io_data;
        ssize_t res;

        ENTER();

        if (!is_sync_kiocb(kiocb)) {
                p = kmalloc(sizeof(io_data), GFP_KERNEL);
                if (unlikely(!p))
                        return -ENOMEM;
                p->aio = true;
        } else {
                p->aio = false;
        }

        p->read = true;
        p->kiocb = kiocb;
        if (p->aio) {
                p->to_free = dup_iter(&p->data, to, GFP_KERNEL);
                if (!p->to_free) {
                        kfree(p);
                        return -ENOMEM;
                }
        } else {
                p->data = *to;
                p->to_free = NULL;
        }
        p->mm = current->mm;

        kiocb->private = p;

        if (p->aio)
                kiocb_set_cancel_fn(kiocb, ffs_aio_cancel);

        res = ffs_epfile_io(kiocb->ki_filp, p);
        if (res == -EIOCBQUEUED)
                return res;

        if (p->aio) {
                kfree(p->to_free);
                kfree(p);
        } else {
                *to = p->data;
        }
        return res;
}

static int
ffs_epfile_release(struct inode *inode, struct file *file)
{
        struct ffs_epfile *epfile = inode->i_private;

        ENTER();

        __ffs_epfile_read_buffer_free(epfile);
        ffs_data_closed(epfile->ffs);

        return 0;
}

static long ffs_epfile_ioctl(struct file *file, unsigned code,
                             unsigned long value)
{
        struct ffs_epfile *epfile = file->private_data;
        struct ffs_ep *ep;
        int ret;

        ENTER();

        if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
                return -ENODEV;

        /* Wait for endpoint to be enabled */
        ep = epfile->ep;
        if (!ep) {
                if (file->f_flags & O_NONBLOCK)
                        return -EAGAIN;

                ret = wait_event_interruptible(
                                epfile->ffs->wait, (ep = epfile->ep));
                if (ret)
                        return -EINTR;
        }

        spin_lock_irq(&epfile->ffs->eps_lock);

        /* In the meantime, endpoint got disabled or changed. */
        if (epfile->ep != ep) {
                spin_unlock_irq(&epfile->ffs->eps_lock);
                return -ESHUTDOWN;
        }

        switch (code) {
        case FUNCTIONFS_FIFO_STATUS:
                ret = usb_ep_fifo_status(epfile->ep->ep);
                break;
        case FUNCTIONFS_FIFO_FLUSH:
                usb_ep_fifo_flush(epfile->ep->ep);
                ret = 0;
                break;
        case FUNCTIONFS_CLEAR_HALT:
                ret = usb_ep_clear_halt(epfile->ep->ep);
                break;
        case FUNCTIONFS_ENDPOINT_REVMAP:
                ret = epfile->ep->num;
                break;
        case FUNCTIONFS_ENDPOINT_DESC:
        {
                int desc_idx;
                struct usb_endpoint_descriptor *desc;

                switch (epfile->ffs->gadget->speed) {
                case USB_SPEED_SUPER:
                        desc_idx = 2;
                        break;
                case USB_SPEED_HIGH:
                        desc_idx = 1;
                        break;
                default:
                        desc_idx = 0;
                }
                desc = epfile->ep->descs[desc_idx];

                spin_unlock_irq(&epfile->ffs->eps_lock);
                ret = copy_to_user((void *)value, desc, desc->bLength);
                if (ret)
                        ret = -EFAULT;
                return ret;
        }
        default:
                ret = -ENOTTY;
        }
        spin_unlock_irq(&epfile->ffs->eps_lock);

        return ret;
}

static const struct file_operations ffs_epfile_operations = {
        .llseek =       no_llseek,

        .open =         ffs_epfile_open,
        .write_iter =   ffs_epfile_write_iter,
        .read_iter =    ffs_epfile_read_iter,
        .release =      ffs_epfile_release,
        .unlocked_ioctl =       ffs_epfile_ioctl,
};


/* File system and super block operations ***********************************/

/*
 * Mounting the file system creates a controller file, used first for
 * function configuration then later for event monitoring.
 */

static struct inode *__must_check
ffs_sb_make_inode(struct super_block *sb, void *data,
                  const struct file_operations *fops,
                  const struct inode_operations *iops,
                  struct ffs_file_perms *perms)
{
        struct inode *inode;

        ENTER();

        inode = new_inode(sb);

        if (likely(inode)) {
                struct timespec ts = current_time(inode);

                inode->i_ino     = get_next_ino();
                inode->i_mode    = perms->mode;
                inode->i_uid     = perms->uid;
                inode->i_gid     = perms->gid;
                inode->i_atime   = ts;
                inode->i_mtime   = ts;
                inode->i_ctime   = ts;
                inode->i_private = data;
                if (fops)
                        inode->i_fop = fops;
                if (iops)
                        inode->i_op  = iops;
        }

        return inode;
}

/* Create "regular" file */
static struct dentry *ffs_sb_create_file(struct super_block *sb,
                                        const char *name, void *data,
                                        const struct file_operations *fops)
{
        struct ffs_data *ffs = sb->s_fs_info;
        struct dentry   *dentry;
        struct inode    *inode;

        ENTER();

        dentry = d_alloc_name(sb->s_root, name);
        if (unlikely(!dentry))
                return NULL;

        inode = ffs_sb_make_inode(sb, data, fops, NULL, &ffs->file_perms);
        if (unlikely(!inode)) {
                dput(dentry);
                return NULL;
        }

        d_add(dentry, inode);
        return dentry;
}

/* Super block */
static const struct super_operations ffs_sb_operations = {
        .statfs =       simple_statfs,
        .drop_inode =   generic_delete_inode,
};

struct ffs_sb_fill_data {
        struct ffs_file_perms perms;
        umode_t root_mode;
        const char *dev_name;
        bool no_disconnect;
        struct ffs_data *ffs_data;
};

static int ffs_sb_fill(struct super_block *sb, void *_data, int silent)
{
        struct ffs_sb_fill_data *data = _data;
        struct inode    *inode;
        struct ffs_data *ffs = data->ffs_data;

        ENTER();

        ffs->sb              = sb;
        data->ffs_data       = NULL;
        sb->s_fs_info        = ffs;
        sb->s_blocksize      = PAGE_SIZE;
        sb->s_blocksize_bits = PAGE_SHIFT;
        sb->s_magic          = FUNCTIONFS_MAGIC;
        sb->s_op             = &ffs_sb_operations;
        sb->s_time_gran      = 1;

        /* Root inode */
        data->perms.mode = data->root_mode;
        inode = ffs_sb_make_inode(sb, NULL,
                                  &simple_dir_operations,
                                  &simple_dir_inode_operations,
                                  &data->perms);
        sb->s_root = d_make_root(inode);
        if (unlikely(!sb->s_root))
                return -ENOMEM;

        /* EP0 file */
        if (unlikely(!ffs_sb_create_file(sb, "ep0", ffs,
                                         &ffs_ep0_operations)))
                return -ENOMEM;

        return 0;
}

static int ffs_fs_parse_opts(struct ffs_sb_fill_data *data, char *opts)
{
        ENTER();

        if (!opts || !*opts)
                return 0;

        for (;;) {
                unsigned long value;
                char *eq, *comma;

                /* Option limit */
                comma = strchr(opts, ',');
                if (comma)
                        *comma = 0;

                /* Value limit */
                eq = strchr(opts, '=');
                if (unlikely(!eq)) {
                        pr_err("'=' missing in %s\n", opts);
                        return -EINVAL;
                }
                *eq = 0;

                /* Parse value */
                if (kstrtoul(eq + 1, 0, &value)) {
                        pr_err("%s: invalid value: %s\n", opts, eq + 1);
                        return -EINVAL;
                }

                /* Interpret option */
                switch (eq - opts) {
                case 13:
                        if (!memcmp(opts, "no_disconnect", 13))
                                data->no_disconnect = !!value;
                        else
                                goto invalid;
                        break;
                case 5:
                        if (!memcmp(opts, "rmode", 5))
                                data->root_mode  = (value & 0555) | S_IFDIR;
                        else if (!memcmp(opts, "fmode", 5))
                                data->perms.mode = (value & 0666) | S_IFREG;
                        else
                                goto invalid;
                        break;

                case 4:
                        if (!memcmp(opts, "mode", 4)) {
                                data->root_mode  = (value & 0555) | S_IFDIR;
                                data->perms.mode = (value & 0666) | S_IFREG;
                        } else {
                                goto invalid;
                        }
                        break;

                case 3:
                        if (!memcmp(opts, "uid", 3)) {
                                data->perms.uid = make_kuid(current_user_ns(), value);
                                if (!uid_valid(data->perms.uid)) {
                                        pr_err("%s: unmapped value: %lu\n", opts, value);
                                        return -EINVAL;
                                }
                        } else if (!memcmp(opts, "gid", 3)) {
                                data->perms.gid = make_kgid(current_user_ns(), value);
                                if (!gid_valid(data->perms.gid)) {
                                        pr_err("%s: unmapped value: %lu\n", opts, value);
                                        return -EINVAL;
                                }
                        } else {
                                goto invalid;
                        }
                        break;

                default:
invalid:
                        pr_err("%s: invalid option\n", opts);
                        return -EINVAL;
                }

                /* Next iteration */
                if (!comma)
                        break;
                opts = comma + 1;
        }

        return 0;
}

/* "mount -t functionfs dev_name /dev/function" ends up here */

static struct dentry *
ffs_fs_mount(struct file_system_type *t, int flags,
              const char *dev_name, void *opts)
{
        struct ffs_sb_fill_data data = {
                .perms = {
                        .mode = S_IFREG | 0600,
                        .uid = GLOBAL_ROOT_UID,
                        .gid = GLOBAL_ROOT_GID,
                },
                .root_mode = S_IFDIR | 0500,
                .no_disconnect = false,
        };
        struct dentry *rv;
        int ret;
        void *ffs_dev;
        struct ffs_data *ffs;

        ENTER();

        ret = ffs_fs_parse_opts(&data, opts);
        if (unlikely(ret < 0))
                return ERR_PTR(ret);

        ffs = ffs_data_new(dev_name);
        if (unlikely(!ffs))
                return ERR_PTR(-ENOMEM);
        ffs->file_perms = data.perms;
        ffs->no_disconnect = data.no_disconnect;

        ffs->dev_name = kstrdup(dev_name, GFP_KERNEL);
        if (unlikely(!ffs->dev_name)) {
                ffs_data_put(ffs);
                return ERR_PTR(-ENOMEM);
        }

        ffs_dev = ffs_acquire_dev(dev_name);
        if (IS_ERR(ffs_dev)) {
                ffs_data_put(ffs);
                return ERR_CAST(ffs_dev);
        }
        ffs->private_data = ffs_dev;
        data.ffs_data = ffs;

        rv = mount_nodev(t, flags, &data, ffs_sb_fill);
        if (IS_ERR(rv) && data.ffs_data) {
                ffs_release_dev(data.ffs_data);
                ffs_data_put(data.ffs_data);
        }
        return rv;
}

static void
ffs_fs_kill_sb(struct super_block *sb)
{
        ENTER();

        kill_litter_super(sb);
        if (sb->s_fs_info) {
                ffs_release_dev(sb->s_fs_info);
                ffs_data_closed(sb->s_fs_info);
        }
}

static struct file_system_type ffs_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "functionfs",
        .mount          = ffs_fs_mount,
        .kill_sb        = ffs_fs_kill_sb,
};
MODULE_ALIAS_FS("functionfs");


/* Driver's main init/cleanup functions *************************************/

static int functionfs_init(void)
{
        int ret;

        ENTER();

        ret = register_filesystem(&ffs_fs_type);
        if (likely(!ret))
                pr_info("file system registered\n");
        else
                pr_err("failed registering file system (%d)\n", ret);

        return ret;
}

static void functionfs_cleanup(void)
{
        ENTER();

        pr_info("unloading\n");
        unregister_filesystem(&ffs_fs_type);
}


/* ffs_data and ffs_function construction and destruction code **************/

static void ffs_data_clear(struct ffs_data *ffs);
static void ffs_data_reset(struct ffs_data *ffs);

static void ffs_data_get(struct ffs_data *ffs)
{
        ENTER();

        refcount_inc(&ffs->ref);
}

static void ffs_data_opened(struct ffs_data *ffs)
{
        ENTER();

        refcount_inc(&ffs->ref);
        if (atomic_add_return(1, &ffs->opened) == 1 &&
                        ffs->state == FFS_DEACTIVATED) {
                ffs->state = FFS_CLOSING;
                ffs_data_reset(ffs);
        }
}

static void ffs_data_put(struct ffs_data *ffs)
{
        ENTER();

        if (unlikely(refcount_dec_and_test(&ffs->ref))) {
                pr_info("%s(): freeing\n", __func__);
                ffs_data_clear(ffs);
                BUG_ON(waitqueue_active(&ffs->ev.waitq) ||
                       waitqueue_active(&ffs->ep0req_completion.wait) ||
                       waitqueue_active(&ffs->wait));
                destroy_workqueue(ffs->io_completion_wq);
                kfree(ffs->dev_name);
                kfree(ffs);
        }
}

static void ffs_data_closed(struct ffs_data *ffs)
{
        ENTER();

        if (atomic_dec_and_test(&ffs->opened)) {
                if (ffs->no_disconnect) {
                        ffs->state = FFS_DEACTIVATED;
                        if (ffs->epfiles) {
                                ffs_epfiles_destroy(ffs->epfiles,
                                                   ffs->eps_count);
                                ffs->epfiles = NULL;
                        }
                        if (ffs->setup_state == FFS_SETUP_PENDING)
                                __ffs_ep0_stall(ffs);
                } else {
                        ffs->state = FFS_CLOSING;
                        ffs_data_reset(ffs);
                }
        }
        if (atomic_read(&ffs->opened) < 0) {
                ffs->state = FFS_CLOSING;
                ffs_data_reset(ffs);
        }

        ffs_data_put(ffs);
}

static struct ffs_data *ffs_data_new(const char *dev_name)
{
        struct ffs_data *ffs = kzalloc(sizeof *ffs, GFP_KERNEL);
        if (unlikely(!ffs))
                return NULL;

        ENTER();

        ffs->io_completion_wq = alloc_ordered_workqueue("%s", 0, dev_name);
        if (!ffs->io_completion_wq) {
                kfree(ffs);
                return NULL;
        }

        refcount_set(&ffs->ref, 1);
        atomic_set(&ffs->opened, 0);
        ffs->state = FFS_READ_DESCRIPTORS;
        mutex_init(&ffs->mutex);
        spin_lock_init(&ffs->eps_lock);
        init_waitqueue_head(&ffs->ev.waitq);
        init_waitqueue_head(&ffs->wait);
        init_completion(&ffs->ep0req_completion);

        /* XXX REVISIT need to update it in some places, or do we? */
        ffs->ev.can_stall = 1;

        return ffs;
}

static void ffs_data_clear(struct ffs_data *ffs)
{
        ENTER();

        ffs_closed(ffs);

        BUG_ON(ffs->gadget);

        if (ffs->epfiles)
                ffs_epfiles_destroy(ffs->epfiles, ffs->eps_count);

        if (ffs->ffs_eventfd)
                eventfd_ctx_put(ffs->ffs_eventfd);

        kfree(ffs->raw_descs_data);
        kfree(ffs->raw_strings);
        kfree(ffs->stringtabs);
}

static void ffs_data_reset(struct ffs_data *ffs)
{
        ENTER();

        ffs_data_clear(ffs);

        ffs->epfiles = NULL;
        ffs->raw_descs_data = NULL;
        ffs->raw_descs = NULL;
        ffs->raw_strings = NULL;
        ffs->stringtabs = NULL;

        ffs->raw_descs_length = 0;
        ffs->fs_descs_count = 0;
        ffs->hs_descs_count = 0;
        ffs->ss_descs_count = 0;

        ffs->strings_count = 0;
        ffs->interfaces_count = 0;
        ffs->eps_count = 0;

        ffs->ev.count = 0;

        ffs->state = FFS_READ_DESCRIPTORS;
        ffs->setup_state = FFS_NO_SETUP;
        ffs->flags = 0;
}


static int functionfs_bind(struct ffs_data *ffs, struct usb_composite_dev *cdev)
{
        struct usb_gadget_strings **lang;
        int first_id;

        ENTER();

        if (WARN_ON(ffs->state != FFS_ACTIVE
                 || test_and_set_bit(FFS_FL_BOUND, &ffs->flags)))
                return -EBADFD;

        first_id = usb_string_ids_n(cdev, ffs->strings_count);
        if (unlikely(first_id < 0))
                return first_id;

        ffs->ep0req = usb_ep_alloc_request(cdev->gadget->ep0, GFP_KERNEL);
        if (unlikely(!ffs->ep0req))
                return -ENOMEM;
        ffs->ep0req->complete = ffs_ep0_complete;
        ffs->ep0req->context = ffs;

        lang = ffs->stringtabs;
        if (lang) {
                for (; *lang; ++lang) {
                        struct usb_string *str = (*lang)->strings;
                        int id = first_id;
                        for (; str->s; ++id, ++str)
                                str->id = id;
                }
        }

        ffs->gadget = cdev->gadget;
        ffs_data_get(ffs);
        return 0;
}

static void functionfs_unbind(struct ffs_data *ffs)
{
        ENTER();

        if (!WARN_ON(!ffs->gadget)) {
                usb_ep_free_request(ffs->gadget->ep0, ffs->ep0req);
                ffs->ep0req = NULL;
                ffs->gadget = NULL;
                clear_bit(FFS_FL_BOUND, &ffs->flags);
                ffs_data_put(ffs);
        }
}

static int ffs_epfiles_create(struct ffs_data *ffs)
{
        struct ffs_epfile *epfile, *epfiles;
        unsigned i, count;

        ENTER();

        count = ffs->eps_count;
        epfiles = kcalloc(count, sizeof(*epfiles), GFP_KERNEL);
        if (!epfiles)
                return -ENOMEM;

        epfile = epfiles;
        for (i = 1; i <= count; ++i, ++epfile) {
                epfile->ffs = ffs;
                mutex_init(&epfile->mutex);
                if (ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
                        sprintf(epfile->name, "ep%02x", ffs->eps_addrmap[i]);
                else
                        sprintf(epfile->name, "ep%u", i);
                epfile->dentry = ffs_sb_create_file(ffs->sb, epfile->name,
                                                 epfile,
                                                 &ffs_epfile_operations);
                if (unlikely(!epfile->dentry)) {
                        ffs_epfiles_destroy(epfiles, i - 1);
                        return -ENOMEM;
                }
        }

        ffs->epfiles = epfiles;
        return 0;
}

static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count)
{
        struct ffs_epfile *epfile = epfiles;

        ENTER();

        for (; count; --count, ++epfile) {
                BUG_ON(mutex_is_locked(&epfile->mutex));
                if (epfile->dentry) {
                        d_delete(epfile->dentry);
                        dput(epfile->dentry);
                        epfile->dentry = NULL;
                }
        }

        kfree(epfiles);
}

static void ffs_func_eps_disable(struct ffs_function *func)
{
        struct ffs_ep *ep         = func->eps;
        struct ffs_epfile *epfile = func->ffs->epfiles;
        unsigned count            = func->ffs->eps_count;
        unsigned long flags;

        spin_lock_irqsave(&func->ffs->eps_lock, flags);
        while (count--) {
                /* pending requests get nuked */
                if (likely(ep->ep))
                        usb_ep_disable(ep->ep);
                ++ep;

                if (epfile) {
                        epfile->ep = NULL;
                        __ffs_epfile_read_buffer_free(epfile);
                        ++epfile;
                }
        }
        spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
}

static int ffs_func_eps_enable(struct ffs_function *func)
{
        struct ffs_data *ffs      = func->ffs;
        struct ffs_ep *ep         = func->eps;
        struct ffs_epfile *epfile = ffs->epfiles;
        unsigned count            = ffs->eps_count;
        unsigned long flags;
        int ret = 0;

        spin_lock_irqsave(&func->ffs->eps_lock, flags);
        while(count--) {
                ep->ep->driver_data = ep;

                ret = config_ep_by_speed(func->gadget, &func->function, ep->ep);
                if (ret) {
                        pr_err("%s: config_ep_by_speed(%s) returned %d\n",
                                        __func__, ep->ep->name, ret);
                        break;
                }

                ret = usb_ep_enable(ep->ep);
                if (likely(!ret)) {
                        epfile->ep = ep;
                        epfile->in = usb_endpoint_dir_in(ep->ep->desc);
                        epfile->isoc = usb_endpoint_xfer_isoc(ep->ep->desc);
                } else {
                        break;
                }

                ++ep;
                ++epfile;
        }

        wake_up_interruptible(&ffs->wait);
        spin_unlock_irqrestore(&func->ffs->eps_lock, flags);

        return ret;
}


/* Parsing and building descriptors and strings *****************************/

/*
 * This validates if data pointed by data is a valid USB descriptor as
 * well as record how many interfaces, endpoints and strings are
 * required by given configuration.  Returns address after the
 * descriptor or NULL if data is invalid.
 */

enum ffs_entity_type {
        FFS_DESCRIPTOR, FFS_INTERFACE, FFS_STRING, FFS_ENDPOINT
};

enum ffs_os_desc_type {
        FFS_OS_DESC, FFS_OS_DESC_EXT_COMPAT, FFS_OS_DESC_EXT_PROP
};

typedef int (*ffs_entity_callback)(enum ffs_entity_type entity,
                                   u8 *valuep,
                                   struct usb_descriptor_header *desc,
                                   void *priv);

typedef int (*ffs_os_desc_callback)(enum ffs_os_desc_type entity,
                                    struct usb_os_desc_header *h, void *data,
                                    unsigned len, void *priv);

static int __must_check ffs_do_single_desc(char *data, unsigned len,
                                           ffs_entity_callback entity,
                                           void *priv)
{
        struct usb_descriptor_header *_ds = (void *)data;
        u8 length;
        int ret;

        ENTER();

        /* At least two bytes are required: length and type */
        if (len < 2) {
                pr_vdebug("descriptor too short\n");
                return -EINVAL;
        }

        /* If we have at least as many bytes as the descriptor takes? */
        length = _ds->bLength;
        if (len < length) {
                pr_vdebug("descriptor longer then available data\n");
                return -EINVAL;
        }

#define __entity_check_INTERFACE(val)  1
#define __entity_check_STRING(val)     (val)
#define __entity_check_ENDPOINT(val)   ((val) & USB_ENDPOINT_NUMBER_MASK)
#define __entity(type, val) do {                                        \
                pr_vdebug("entity " #type "(%02x)\n", (val));           \
                if (unlikely(!__entity_check_ ##type(val))) {           \
                        pr_vdebug("invalid entity's value\n");          \
                        return -EINVAL;                                 \
                }                                                       \
                ret = entity(FFS_ ##type, &val, _ds, priv);             \
                if (unlikely(ret < 0)) {                                \
                        pr_debug("entity " #type "(%02x); ret = %d\n",  \
                                 (val), ret);                           \
                        return ret;                                     \
                }                                                       \
        } while (0)

        /* Parse descriptor depending on type. */
        switch (_ds->bDescriptorType) {
        case USB_DT_DEVICE:
        case USB_DT_CONFIG:
        case USB_DT_STRING:
        case USB_DT_DEVICE_QUALIFIER:
                /* function can't have any of those */
                pr_vdebug("descriptor reserved for gadget: %d\n",
                      _ds->bDescriptorType);
                return -EINVAL;

        case USB_DT_INTERFACE: {
                struct usb_interface_descriptor *ds = (void *)_ds;
                pr_vdebug("interface descriptor\n");
                if (length != sizeof *ds)
                        goto inv_length;

                __entity(INTERFACE, ds->bInterfaceNumber);
                if (ds->iInterface)
                        __entity(STRING, ds->iInterface);
        }
                break;

        case USB_DT_ENDPOINT: {
                struct usb_endpoint_descriptor *ds = (void *)_ds;
                pr_vdebug("endpoint descriptor\n");
                if (length != USB_DT_ENDPOINT_SIZE &&
                    length != USB_DT_ENDPOINT_AUDIO_SIZE)
                        goto inv_length;
                __entity(ENDPOINT, ds->bEndpointAddress);
        }
                break;

        case HID_DT_HID:
                pr_vdebug("hid descriptor\n");
                if (length != sizeof(struct hid_descriptor))
                        goto inv_length;
                break;

        case USB_DT_OTG:
                if (length != sizeof(struct usb_otg_descriptor))
                        goto inv_length;
                break;

        case USB_DT_INTERFACE_ASSOCIATION: {
                struct usb_interface_assoc_descriptor *ds = (void *)_ds;
                pr_vdebug("interface association descriptor\n");
                if (length != sizeof *ds)
                        goto inv_length;
                if (ds->iFunction)
                        __entity(STRING, ds->iFunction);
        }
                break;

        case USB_DT_SS_ENDPOINT_COMP:
                pr_vdebug("EP SS companion descriptor\n");
                if (length != sizeof(struct usb_ss_ep_comp_descriptor))
                        goto inv_length;
                break;

        case USB_DT_OTHER_SPEED_CONFIG:
        case USB_DT_INTERFACE_POWER:
        case USB_DT_DEBUG:
        case USB_DT_SECURITY:
        case USB_DT_CS_RADIO_CONTROL:
                /* TODO */
                pr_vdebug("unimplemented descriptor: %d\n", _ds->bDescriptorType);
                return -EINVAL;

        default:
                /* We should never be here */
                pr_vdebug("unknown descriptor: %d\n", _ds->bDescriptorType);
                return -EINVAL;

inv_length:
                pr_vdebug("invalid length: %d (descriptor %d)\n",
                          _ds->bLength, _ds->bDescriptorType);
                return -EINVAL;
        }

#undef __entity
#undef __entity_check_DESCRIPTOR
#undef __entity_check_INTERFACE
#undef __entity_check_STRING
#undef __entity_check_ENDPOINT

        return length;
}

static int __must_check ffs_do_descs(unsigned count, char *data, unsigned len,
                                     ffs_entity_callback entity, void *priv)
{
        const unsigned _len = len;
        unsigned long num = 0;

        ENTER();

        for (;;) {
                int ret;

                if (num == count)
                        data = NULL;

                /* Record "descriptor" entity */
                ret = entity(FFS_DESCRIPTOR, (u8 *)num, (void *)data, priv);
                if (unlikely(ret < 0)) {
                        pr_debug("entity DESCRIPTOR(%02lx); ret = %d\n",
                                 num, ret);
                        return ret;
                }

                if (!data)
                        return _len - len;

                ret = ffs_do_single_desc(data, len, entity, priv);
                if (unlikely(ret < 0)) {
                        pr_debug("%s returns %d\n", __func__, ret);
                        return ret;
                }

                len -= ret;
                data += ret;
                ++num;
        }
}

static int __ffs_data_do_entity(enum ffs_entity_type type,
                                u8 *valuep, struct usb_descriptor_header *desc,
                                void *priv)
{
        struct ffs_desc_helper *helper = priv;
        struct usb_endpoint_descriptor *d;

        ENTER();

        switch (type) {
        case FFS_DESCRIPTOR:
                break;

        case FFS_INTERFACE:
                /*
                 * Interfaces are indexed from zero so if we
                 * encountered interface "n" then there are at least
                 * "n+1" interfaces.
                 */
                if (*valuep >= helper->interfaces_count)
                        helper->interfaces_count = *valuep + 1;
                break;

        case FFS_STRING:
                /*
                 * Strings are indexed from 1 (0 is reserved
                 * for languages list)
                 */
                if (*valuep > helper->ffs->strings_count)
                        helper->ffs->strings_count = *valuep;
                break;

        case FFS_ENDPOINT:
                d = (void *)desc;
                helper->eps_count++;
                if (helper->eps_count >= FFS_MAX_EPS_COUNT)
                        return -EINVAL;
                /* Check if descriptors for any speed were already parsed */
                if (!helper->ffs->eps_count && !helper->ffs->interfaces_count)
                        helper->ffs->eps_addrmap[helper->eps_count] =
                                d->bEndpointAddress;
                else if (helper->ffs->eps_addrmap[helper->eps_count] !=
                                d->bEndpointAddress)
                        return -EINVAL;
                break;
        }

        return 0;
}

static int __ffs_do_os_desc_header(enum ffs_os_desc_type *next_type,
                                   struct usb_os_desc_header *desc)
{
        u16 bcd_version = le16_to_cpu(desc->bcdVersion);
        u16 w_index = le16_to_cpu(desc->wIndex);

        if (bcd_version != 1) {
                pr_vdebug("unsupported os descriptors version: %d",
                          bcd_version);
                return -EINVAL;
        }
        switch (w_index) {
        case 0x4:
                *next_type = FFS_OS_DESC_EXT_COMPAT;
                break;
        case 0x5:
                *next_type = FFS_OS_DESC_EXT_PROP;
                break;
        default:
                pr_vdebug("unsupported os descriptor type: %d", w_index);
                return -EINVAL;
        }

        return sizeof(*desc);
}

/*
 * Process all extended compatibility/extended property descriptors
 * of a feature descriptor
 */
static int __must_check ffs_do_single_os_desc(char *data, unsigned len,
                                              enum ffs_os_desc_type type,
                                              u16 feature_count,
                                              ffs_os_desc_callback entity,
                                              void *priv,
                                              struct usb_os_desc_header *h)
{
        int ret;
        const unsigned _len = len;

        ENTER();

        /* loop over all ext compat/ext prop descriptors */
        while (feature_count--) {
                ret = entity(type, h, data, len, priv);
                if (unlikely(ret < 0)) {
                        pr_debug("bad OS descriptor, type: %d\n", type);
                        return ret;
                }
                data += ret;
                len -= ret;
        }
        return _len - len;
}

/* Process a number of complete Feature Descriptors (Ext Compat or Ext Prop) */
static int __must_check ffs_do_os_descs(unsigned count,
                                        char *data, unsigned len,
                                        ffs_os_desc_callback entity, void *priv)
{
        const unsigned _len = len;
        unsigned long num = 0;

        ENTER();

        for (num = 0; num < count; ++num) {
                int ret;
                enum ffs_os_desc_type type;
                u16 feature_count;
                struct usb_os_desc_header *desc = (void *)data;

                if (len < sizeof(*desc))
                        return -EINVAL;

                /*
                 * Record "descriptor" entity.
                 * Process dwLength, bcdVersion, wIndex, get b/wCount.
                 * Move the data pointer to the beginning of extended
                 * compatibilities proper or extended properties proper
                 * portions of the data
                 */
                if (le32_to_cpu(desc->dwLength) > len)
                        return -EINVAL;

                ret = __ffs_do_os_desc_header(&type, desc);
                if (unlikely(ret < 0)) {
                        pr_debug("entity OS_DESCRIPTOR(%02lx); ret = %d\n",
                                 num, ret);
                        return ret;
                }
                /*
                 * 16-bit hex "?? 00" Little Endian looks like 8-bit hex "??"
                 */
                feature_count = le16_to_cpu(desc->wCount);
                if (type == FFS_OS_DESC_EXT_COMPAT &&
                    (feature_count > 255 || desc->Reserved))
                                return -EINVAL;
                len -= ret;
                data += ret;

                /*
                 * Process all function/property descriptors
                 * of this Feature Descriptor
                 */
                ret = ffs_do_single_os_desc(data, len, type,
                                            feature_count, entity, priv, desc);
                if (unlikely(ret < 0)) {
                        pr_debug("%s returns %d\n", __func__, ret);
                        return ret;
                }

                len -= ret;
                data += ret;
        }
        return _len - len;
}

/**
 * Validate contents of the buffer from userspace related to OS descriptors.
 */
static int __ffs_data_do_os_desc(enum ffs_os_desc_type type,
                                 struct usb_os_desc_header *h, void *data,
                                 unsigned len, void *priv)
{
        struct ffs_data *ffs = priv;
        u8 length;

        ENTER();

        switch (type) {
        case FFS_OS_DESC_EXT_COMPAT: {
                struct usb_ext_compat_desc *d = data;
                int i;

                if (len < sizeof(*d) ||
                    d->bFirstInterfaceNumber >= ffs->interfaces_count)
                        return -EINVAL;
                if (d->Reserved1 != 1) {
                        /*
                         * According to the spec, Reserved1 must be set to 1
                         * but older kernels incorrectly rejected non-zero
                         * values.  We fix it here to avoid returning EINVAL
                         * in response to values we used to accept.
                         */
                        pr_debug("usb_ext_compat_desc::Reserved1 forced to 1\n");
                        d->Reserved1 = 1;
                }
                for (i = 0; i < ARRAY_SIZE(d->Reserved2); ++i)
                        if (d->Reserved2[i])
                                return -EINVAL;

                length = sizeof(struct usb_ext_compat_desc);
        }
                break;
        case FFS_OS_DESC_EXT_PROP: {
                struct usb_ext_prop_desc *d = data;
                u32 type, pdl;
                u16 pnl;

                if (len < sizeof(*d) || h->interface >= ffs->interfaces_count)
                        return -EINVAL;
                length = le32_to_cpu(d->dwSize);
                if (len < length)
                        return -EINVAL;
                type = le32_to_cpu(d->dwPropertyDataType);
                if (type < USB_EXT_PROP_UNICODE ||
                    type > USB_EXT_PROP_UNICODE_MULTI) {
                        pr_vdebug("unsupported os descriptor property type: %d",
                                  type);
                        return -EINVAL;
                }
                pnl = le16_to_cpu(d->wPropertyNameLength);
                if (length < 14 + pnl) {
                        pr_vdebug("invalid os descriptor length: %d pnl:%d (descriptor %d)\n",
                                  length, pnl, type);
                        return -EINVAL;
                }
                pdl = le32_to_cpu(*(u32 *)((u8 *)data + 10 + pnl));
                if (length != 14 + pnl + pdl) {
                        pr_vdebug("invalid os descriptor length: %d pnl:%d pdl:%d (descriptor %d)\n",
                                  length, pnl, pdl, type);
                        return -EINVAL;
                }
                ++ffs->ms_os_descs_ext_prop_count;
                /* property name reported to the host as "WCHAR"s */
                ffs->ms_os_descs_ext_prop_name_len += pnl * 2;
                ffs->ms_os_descs_ext_prop_data_len += pdl;
        }
                break;
        default:
                pr_vdebug("unknown descriptor: %d\n", type);
                return -EINVAL;
        }
        return length;
}

static int __ffs_data_got_descs(struct ffs_data *ffs,
                                char *const _data, size_t len)
{
        char *data = _data, *raw_descs;
        unsigned os_descs_count = 0, counts[3], flags;
        int ret = -EINVAL, i;
        struct ffs_desc_helper helper;

        ENTER();

        if (get_unaligned_le32(data + 4) != len)
                goto error;

        switch (get_unaligned_le32(data)) {
        case FUNCTIONFS_DESCRIPTORS_MAGIC:
                flags = FUNCTIONFS_HAS_FS_DESC | FUNCTIONFS_HAS_HS_DESC;
                data += 8;
                len  -= 8;
                break;
        case FUNCTIONFS_DESCRIPTORS_MAGIC_V2:
                flags = get_unaligned_le32(data + 8);
                ffs->user_flags = flags;
                if (flags & ~(FUNCTIONFS_HAS_FS_DESC |
                              FUNCTIONFS_HAS_HS_DESC |
                              FUNCTIONFS_HAS_SS_DESC |
                              FUNCTIONFS_HAS_MS_OS_DESC |
                              FUNCTIONFS_VIRTUAL_ADDR |
                              FUNCTIONFS_EVENTFD |
                              FUNCTIONFS_ALL_CTRL_RECIP |
                              FUNCTIONFS_CONFIG0_SETUP)) {
                        ret = -ENOSYS;
                        goto error;
                }
                data += 12;
                len  -= 12;
                break;
        default:
                goto error;
        }

        if (flags & FUNCTIONFS_EVENTFD) {
                if (len < 4)
                        goto error;
                ffs->ffs_eventfd =
                        eventfd_ctx_fdget((int)get_unaligned_le32(data));
                if (IS_ERR(ffs->ffs_eventfd)) {
                        ret = PTR_ERR(ffs->ffs_eventfd);
                        ffs->ffs_eventfd = NULL;
                        goto error;
                }
                data += 4;
                len  -= 4;
        }

        /* Read fs_count, hs_count and ss_count (if present) */
        for (i = 0; i < 3; ++i) {
                if (!(flags & (1 << i))) {
                        counts[i] = 0;
                } else if (len < 4) {
                        goto error;
                } else {
                        counts[i] = get_unaligned_le32(data);
                        data += 4;
                        len  -= 4;
                }
        }
        if (flags & (1 << i)) {
                if (len < 4) {
                        goto error;
                }
                os_descs_count = get_unaligned_le32(data);
                data += 4;
                len -= 4;
        };

        /* Read descriptors */
        raw_descs = data;
        helper.ffs = ffs;
        for (i = 0; i < 3; ++i) {
                if (!counts[i])
                        continue;
                helper.interfaces_count = 0;
                helper.eps_count = 0;
                ret = ffs_do_descs(counts[i], data, len,
                                   __ffs_data_do_entity, &helper);
                if (ret < 0)
                        goto error;
                if (!ffs->eps_count && !ffs->interfaces_count) {
                        ffs->eps_count = helper.eps_count;
                        ffs->interfaces_count = helper.interfaces_count;
                } else {
                        if (ffs->eps_count != helper.eps_count) {
                                ret = -EINVAL;
                                goto error;
                        }
                        if (ffs->interfaces_count != helper.interfaces_count) {
                                ret = -EINVAL;
                                goto error;
                        }
                }
                data += ret;
                len  -= ret;
        }
        if (os_descs_count) {
                ret = ffs_do_os_descs(os_descs_count, data, len,
                                      __ffs_data_do_os_desc, ffs);
                if (ret < 0)
                        goto error;
                data += ret;
                len -= ret;
        }

        if (raw_descs == data || len) {
                ret = -EINVAL;
                goto error;
        }

        ffs->raw_descs_data     = _data;
        ffs->raw_descs          = raw_descs;
        ffs->raw_descs_length   = data - raw_descs;
        ffs->fs_descs_count     = counts[0];
        ffs->hs_descs_count     = counts[1];
        ffs->ss_descs_count     = counts[2];
        ffs->ms_os_descs_count  = os_descs_count;

        return 0;

error:
        kfree(_data);
        return ret;
}

static int __ffs_data_got_strings(struct ffs_data *ffs,
                                  char *const _data, size_t len)
{
        u32 str_count, needed_count, lang_count;
        struct usb_gadget_strings **stringtabs, *t;
        const char *data = _data;
        struct usb_string *s;

        ENTER();

        if (unlikely(len < 16 ||
                     get_unaligned_le32(data) != FUNCTIONFS_STRINGS_MAGIC ||
                     get_unaligned_le32(data + 4) != len))
                goto error;
        str_count  = get_unaligned_le32(data + 8);
        lang_count = get_unaligned_le32(data + 12);

        /* if one is zero the other must be zero */
        if (unlikely(!str_count != !lang_count))
                goto error;

        /* Do we have at least as many strings as descriptors need? */
        needed_count = ffs->strings_count;
        if (unlikely(str_count < needed_count))
                goto error;

        /*
         * If we don't need any strings just return and free all
         * memory.
         */
        if (!needed_count) {
                kfree(_data);
                return 0;
        }

        /* Allocate everything in one chunk so there's less maintenance. */
        {
                unsigned i = 0;
                vla_group(d);
                vla_item(d, struct usb_gadget_strings *, stringtabs,
                        lang_count + 1);
                vla_item(d, struct usb_gadget_strings, stringtab, lang_count);
                vla_item(d, struct usb_string, strings,
                        lang_count*(needed_count+1));

                char *vlabuf = kmalloc(vla_group_size(d), GFP_KERNEL);

                if (unlikely(!vlabuf)) {
                        kfree(_data);
                        return -ENOMEM;
                }

                /* Initialize the VLA pointers */
                stringtabs = vla_ptr(vlabuf, d, stringtabs);
                t = vla_ptr(vlabuf, d, stringtab);
                i = lang_count;
                do {
                        *stringtabs++ = t++;
                } while (--i);
                *stringtabs = NULL;

                /* stringtabs = vlabuf = d_stringtabs for later kfree */
                stringtabs = vla_ptr(vlabuf, d, stringtabs);
                t = vla_ptr(vlabuf, d, stringtab);
                s = vla_ptr(vlabuf, d, strings);
        }

        /* For each language */
        data += 16;
        len -= 16;

        do { /* lang_count > 0 so we can use do-while */
                unsigned needed = needed_count;

                if (unlikely(len < 3))
                        goto error_free;
                t->language = get_unaligned_le16(data);
                t->strings  = s;
                ++t;

                data += 2;
                len -= 2;

                /* For each string */
                do { /* str_count > 0 so we can use do-while */
                        size_t length = strnlen(data, len);

                        if (unlikely(length == len))
                                goto error_free;

                        /*
                         * User may provide more strings then we need,
                         * if that's the case we simply ignore the
                         * rest
                         */
                        if (likely(needed)) {
                                /*
                                 * s->id will be set while adding
                                 * function to configuration so for
                                 * now just leave garbage here.
                                 */
                                s->s = data;
                                --needed;
                                ++s;
                        }

                        data += length + 1;
                        len -= length + 1;
                } while (--str_count);

                s->id = 0;   /* terminator */
                s->s = NULL;
                ++s;

        } while (--lang_count);

        /* Some garbage left? */
        if (unlikely(len))
                goto error_free;

        /* Done! */
        ffs->stringtabs = stringtabs;
        ffs->raw_strings = _data;

        return 0;

error_free:
        kfree(stringtabs);
error:
        kfree(_data);
        return -EINVAL;
}


/* Events handling and management *******************************************/

static void __ffs_event_add(struct ffs_data *ffs,
                            enum usb_functionfs_event_type type)
{
        enum usb_functionfs_event_type rem_type1, rem_type2 = type;
        int neg = 0;

        /*
         * Abort any unhandled setup
         *
         * We do not need to worry about some cmpxchg() changing value
         * of ffs->setup_state without holding the lock because when
         * state is FFS_SETUP_PENDING cmpxchg() in several places in
         * the source does nothing.
         */
        if (ffs->setup_state == FFS_SETUP_PENDING)
                ffs->setup_state = FFS_SETUP_CANCELLED;

        /*
         * Logic of this function guarantees that there are at most four pending
         * evens on ffs->ev.types queue.  This is important because the queue
         * has space for four elements only and __ffs_ep0_read_events function
         * depends on that limit as well.  If more event types are added, those
         * limits have to be revisited or guaranteed to still hold.
         */
        switch (type) {
        case FUNCTIONFS_RESUME:
                rem_type2 = FUNCTIONFS_SUSPEND;
                /* FALL THROUGH */
        case FUNCTIONFS_SUSPEND:
        case FUNCTIONFS_SETUP:
                rem_type1 = type;
                /* Discard all similar events */
                break;

        case FUNCTIONFS_BIND:
        case FUNCTIONFS_UNBIND:
        case FUNCTIONFS_DISABLE:
        case FUNCTIONFS_ENABLE:
                /* Discard everything other then power management. */
                rem_type1 = FUNCTIONFS_SUSPEND;
                rem_type2 = FUNCTIONFS_RESUME;
                neg = 1;
                break;

        default:
                WARN(1, "%d: unknown event, this should not happen\n", type);
                return;
        }

        {
                u8 *ev  = ffs->ev.types, *out = ev;
                unsigned n = ffs->ev.count;
                for (; n; --n, ++ev)
                        if ((*ev == rem_type1 || *ev == rem_type2) == neg)
                                *out++ = *ev;
                        else
                                pr_vdebug("purging event %d\n", *ev);
                ffs->ev.count = out - ffs->ev.types;
        }

        pr_vdebug("adding event %d\n", type);
        ffs->ev.types[ffs->ev.count++] = type;
        wake_up_locked(&ffs->ev.waitq);
        if (ffs->ffs_eventfd)
                eventfd_signal(ffs->ffs_eventfd, 1);
}

static void ffs_event_add(struct ffs_data *ffs,
                          enum usb_functionfs_event_type type)
{
        unsigned long flags;
        spin_lock_irqsave(&ffs->ev.waitq.lock, flags);
        __ffs_event_add(ffs, type);
        spin_unlock_irqrestore(&ffs->ev.waitq.lock, flags);
}

/* Bind/unbind USB function hooks *******************************************/

static int ffs_ep_addr2idx(struct ffs_data *ffs, u8 endpoint_address)
{
        int i;

        for (i = 1; i < ARRAY_SIZE(ffs->eps_addrmap); ++i)
                if (ffs->eps_addrmap[i] == endpoint_address)
                        return i;
        return -ENOENT;
}

static int __ffs_func_bind_do_descs(enum ffs_entity_type type, u8 *valuep,
                                    struct usb_descriptor_header *desc,
                                    void *priv)
{
        struct usb_endpoint_descriptor *ds = (void *)desc;
        struct ffs_function *func = priv;
        struct ffs_ep *ffs_ep;
        unsigned ep_desc_id;
        int idx;
        static const char *speed_names[] = { "full", "high", "super" };

        if (type != FFS_DESCRIPTOR)
                return 0;

        /*
         * If ss_descriptors is not NULL, we are reading super speed
         * descriptors; if hs_descriptors is not NULL, we are reading high
         * speed descriptors; otherwise, we are reading full speed
         * descriptors.
         */
        if (func->function.ss_descriptors) {
                ep_desc_id = 2;
                func->function.ss_descriptors[(long)valuep] = desc;
        } else if (func->function.hs_descriptors) {
                ep_desc_id = 1;
                func->function.hs_descriptors[(long)valuep] = desc;
        } else {
                ep_desc_id = 0;
                func->function.fs_descriptors[(long)valuep]    = desc;
        }

        if (!desc || desc->bDescriptorType != USB_DT_ENDPOINT)
                return 0;

        idx = ffs_ep_addr2idx(func->ffs, ds->bEndpointAddress) - 1;
        if (idx < 0)
                return idx;

        ffs_ep = func->eps + idx;

        if (unlikely(ffs_ep->descs[ep_desc_id])) {
                pr_err("two %sspeed descriptors for EP %d\n",
                          speed_names[ep_desc_id],
                          ds->bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
                return -EINVAL;
        }
        ffs_ep->descs[ep_desc_id] = ds;

        ffs_dump_mem(": Original  ep desc", ds, ds->bLength);
        if (ffs_ep->ep) {
                ds->bEndpointAddress = ffs_ep->descs[0]->bEndpointAddress;
                if (!ds->wMaxPacketSize)
                        ds->wMaxPacketSize = ffs_ep->descs[0]->wMaxPacketSize;
        } else {
                struct usb_request *req;
                struct usb_ep *ep;
                u8 bEndpointAddress;

                /*
                 * We back up bEndpointAddress because autoconfig overwrites
                 * it with physical endpoint address.
                 */
                bEndpointAddress = ds->bEndpointAddress;
                pr_vdebug("autoconfig\n");
                ep = usb_ep_autoconfig(func->gadget, ds);
                if (unlikely(!ep))
                        return -ENOTSUPP;
                ep->driver_data = func->eps + idx;

                req = usb_ep_alloc_request(ep, GFP_KERNEL);
                if (unlikely(!req))
                        return -ENOMEM;

                ffs_ep->ep  = ep;
                ffs_ep->req = req;
                func->eps_revmap[ds->bEndpointAddress &
                                 USB_ENDPOINT_NUMBER_MASK] = idx + 1;
                /*
                 * If we use virtual address mapping, we restore
                 * original bEndpointAddress value.
                 */
                if (func->ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
                        ds->bEndpointAddress = bEndpointAddress;
        }
        ffs_dump_mem(": Rewritten ep desc", ds, ds->bLength);

        return 0;
}

static int __ffs_func_bind_do_nums(enum ffs_entity_type type, u8 *valuep,
                                   struct usb_descriptor_header *desc,
                                   void *priv)
{
        struct ffs_function *func = priv;
        unsigned idx;
        u8 newValue;

        switch (type) {
        default:
        case FFS_DESCRIPTOR:
                /* Handled in previous pass by __ffs_func_bind_do_descs() */
                return 0;

        case FFS_INTERFACE:
                idx = *valuep;
                if (func->interfaces_nums[idx] < 0) {
                        int id = usb_interface_id(func->conf, &func->function);
                        if (unlikely(id < 0))
                                return id;
                        func->interfaces_nums[idx] = id;
                }
                newValue = func->interfaces_nums[idx];
                break;

        case FFS_STRING:
                /* String' IDs are allocated when fsf_data is bound to cdev */
                newValue = func->ffs->stringtabs[0]->strings[*valuep - 1].id;
                break;

        case FFS_ENDPOINT:
                /*
                 * USB_DT_ENDPOINT are handled in
                 * __ffs_func_bind_do_descs().
                 */
                if (desc->bDescriptorType == USB_DT_ENDPOINT)
                        return 0;

                idx = (*valuep & USB_ENDPOINT_NUMBER_MASK) - 1;
                if (unlikely(!func->eps[idx].ep))
                        return -EINVAL;

                {
                        struct usb_endpoint_descriptor **descs;
                        descs = func->eps[idx].descs;
                        newValue = descs[descs[0] ? 0 : 1]->bEndpointAddress;
                }
                break;
        }

        pr_vdebug("%02x -> %02x\n", *valuep, newValue);
        *valuep = newValue;
        return 0;
}

static int __ffs_func_bind_do_os_desc(enum ffs_os_desc_type type,
                                      struct usb_os_desc_header *h, void *data,
                                      unsigned len, void *priv)
{
        struct ffs_function *func = priv;
        u8 length = 0;

        switch (type) {
        case FFS_OS_DESC_EXT_COMPAT: {
                struct usb_ext_compat_desc *desc = data;
                struct usb_os_desc_table *t;

                t = &func->function.os_desc_table[desc->bFirstInterfaceNumber];
                t->if_id = func->interfaces_nums[desc->bFirstInterfaceNumber];
                memcpy(t->os_desc->ext_compat_id, &desc->CompatibleID,
                       ARRAY_SIZE(desc->CompatibleID) +
                       ARRAY_SIZE(desc->SubCompatibleID));
                length = sizeof(*desc);
        }
                break;
        case FFS_OS_DESC_EXT_PROP: {
                struct usb_ext_prop_desc *desc = data;
                struct usb_os_desc_table *t;
                struct usb_os_desc_ext_prop *ext_prop;
                char *ext_prop_name;
                char *ext_prop_data;

                t = &func->function.os_desc_table[h->interface];
                t->if_id = func->interfaces_nums[h->interface];

                ext_prop = func->ffs->ms_os_descs_ext_prop_avail;
                func->ffs->ms_os_descs_ext_prop_avail += sizeof(*ext_prop);

                ext_prop->type = le32_to_cpu(desc->dwPropertyDataType);
                ext_prop->name_len = le16_to_cpu(desc->wPropertyNameLength);
                ext_prop->data_len = le32_to_cpu(*(u32 *)
                        usb_ext_prop_data_len_ptr(data, ext_prop->name_len));
                length = ext_prop->name_len + ext_prop->data_len + 14;

                ext_prop_name = func->ffs->ms_os_descs_ext_prop_name_avail;
                func->ffs->ms_os_descs_ext_prop_name_avail +=
                        ext_prop->name_len;

                ext_prop_data = func->ffs->ms_os_descs_ext_prop_data_avail;
                func->ffs->ms_os_descs_ext_prop_data_avail +=
                        ext_prop->data_len;
                memcpy(ext_prop_data,
                       usb_ext_prop_data_ptr(data, ext_prop->name_len),
                       ext_prop->data_len);
                /* unicode data reported to the host as "WCHAR"s */
                switch (ext_prop->type) {
                case USB_EXT_PROP_UNICODE:
                case USB_EXT_PROP_UNICODE_ENV:
                case USB_EXT_PROP_UNICODE_LINK:
                case USB_EXT_PROP_UNICODE_MULTI:
                        ext_prop->data_len *= 2;
                        break;
                }
                ext_prop->data = ext_prop_data;

                memcpy(ext_prop_name, usb_ext_prop_name_ptr(data),
                       ext_prop->name_len);
                /* property name reported to the host as "WCHAR"s */
                ext_prop->name_len *= 2;
                ext_prop->name = ext_prop_name;

                t->os_desc->ext_prop_len +=
                        ext_prop->name_len + ext_prop->data_len + 14;
                ++t->os_desc->ext_prop_count;
                list_add_tail(&ext_prop->entry, &t->os_desc->ext_prop);
        }
                break;
        default:
                pr_vdebug("unknown descriptor: %d\n", type);
        }

        return length;
}

static inline struct f_fs_opts *ffs_do_functionfs_bind(struct usb_function *f,
                                                struct usb_configuration *c)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct f_fs_opts *ffs_opts =
                container_of(f->fi, struct f_fs_opts, func_inst);
        int ret;

        ENTER();

        /*
         * Legacy gadget triggers binding in functionfs_ready_callback,
         * which already uses locking; taking the same lock here would
         * cause a deadlock.
         *
         * Configfs-enabled gadgets however do need ffs_dev_lock.
         */
        if (!ffs_opts->no_configfs)
                ffs_dev_lock();
        ret = ffs_opts->dev->desc_ready ? 0 : -ENODEV;
        func->ffs = ffs_opts->dev->ffs_data;
        if (!ffs_opts->no_configfs)
                ffs_dev_unlock();
        if (ret)
                return ERR_PTR(ret);

        func->conf = c;
        func->gadget = c->cdev->gadget;

        /*
         * in drivers/usb/gadget/configfs.c:configfs_composite_bind()
         * configurations are bound in sequence with list_for_each_entry,
         * in each configuration its functions are bound in sequence
         * with list_for_each_entry, so we assume no race condition
         * with regard to ffs_opts->bound access
         */
        if (!ffs_opts->refcnt) {
                ret = functionfs_bind(func->ffs, c->cdev);
                if (ret)
                        return ERR_PTR(ret);
        }
        ffs_opts->refcnt++;
        func->function.strings = func->ffs->stringtabs;

        return ffs_opts;
}

static int _ffs_func_bind(struct usb_configuration *c,
                          struct usb_function *f)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;

        const int full = !!func->ffs->fs_descs_count;
        const int high = !!func->ffs->hs_descs_count;
        const int super = !!func->ffs->ss_descs_count;

        int fs_len, hs_len, ss_len, ret, i;
        struct ffs_ep *eps_ptr;

        /* Make it a single chunk, less management later on */
        vla_group(d);
        vla_item_with_sz(d, struct ffs_ep, eps, ffs->eps_count);
        vla_item_with_sz(d, struct usb_descriptor_header *, fs_descs,
                full ? ffs->fs_descs_count + 1 : 0);
        vla_item_with_sz(d, struct usb_descriptor_header *, hs_descs,
                high ? ffs->hs_descs_count + 1 : 0);
        vla_item_with_sz(d, struct usb_descriptor_header *, ss_descs,
                super ? ffs->ss_descs_count + 1 : 0);
        vla_item_with_sz(d, short, inums, ffs->interfaces_count);
        vla_item_with_sz(d, struct usb_os_desc_table, os_desc_table,
                         c->cdev->use_os_string ? ffs->interfaces_count : 0);
        vla_item_with_sz(d, char[16], ext_compat,
                         c->cdev->use_os_string ? ffs->interfaces_count : 0);
        vla_item_with_sz(d, struct usb_os_desc, os_desc,
                         c->cdev->use_os_string ? ffs->interfaces_count : 0);
        vla_item_with_sz(d, struct usb_os_desc_ext_prop, ext_prop,
                         ffs->ms_os_descs_ext_prop_count);
        vla_item_with_sz(d, char, ext_prop_name,
                         ffs->ms_os_descs_ext_prop_name_len);
        vla_item_with_sz(d, char, ext_prop_data,
                         ffs->ms_os_descs_ext_prop_data_len);
        vla_item_with_sz(d, char, raw_descs, ffs->raw_descs_length);
        char *vlabuf;

        ENTER();

        /* Has descriptors only for speeds gadget does not support */
        if (unlikely(!(full | high | super)))
                return -ENOTSUPP;

        /* Allocate a single chunk, less management later on */
        vlabuf = kzalloc(vla_group_size(d), GFP_KERNEL);
        if (unlikely(!vlabuf))
                return -ENOMEM;

        ffs->ms_os_descs_ext_prop_avail = vla_ptr(vlabuf, d, ext_prop);
        ffs->ms_os_descs_ext_prop_name_avail =
                vla_ptr(vlabuf, d, ext_prop_name);
        ffs->ms_os_descs_ext_prop_data_avail =
                vla_ptr(vlabuf, d, ext_prop_data);

        /* Copy descriptors  */
        memcpy(vla_ptr(vlabuf, d, raw_descs), ffs->raw_descs,
               ffs->raw_descs_length);

        memset(vla_ptr(vlabuf, d, inums), 0xff, d_inums__sz);
        eps_ptr = vla_ptr(vlabuf, d, eps);
        for (i = 0; i < ffs->eps_count; i++)
                eps_ptr[i].num = -1;

        /* Save pointers
         * d_eps == vlabuf, func->eps used to kfree vlabuf later
        */
        func->eps             = vla_ptr(vlabuf, d, eps);
        func->interfaces_nums = vla_ptr(vlabuf, d, inums);

        /*
         * Go through all the endpoint descriptors and allocate
         * endpoints first, so that later we can rewrite the endpoint
         * numbers without worrying that it may be described later on.
         */
        if (likely(full)) {
                func->function.fs_descriptors = vla_ptr(vlabuf, d, fs_descs);
                fs_len = ffs_do_descs(ffs->fs_descs_count,
                                      vla_ptr(vlabuf, d, raw_descs),
                                      d_raw_descs__sz,
                                      __ffs_func_bind_do_descs, func);
                if (unlikely(fs_len < 0)) {
                        ret = fs_len;
                        goto error;
                }
        } else {
                fs_len = 0;
        }

        if (likely(high)) {
                func->function.hs_descriptors = vla_ptr(vlabuf, d, hs_descs);
                hs_len = ffs_do_descs(ffs->hs_descs_count,
                                      vla_ptr(vlabuf, d, raw_descs) + fs_len,
                                      d_raw_descs__sz - fs_len,
                                      __ffs_func_bind_do_descs, func);
                if (unlikely(hs_len < 0)) {
                        ret = hs_len;
                        goto error;
                }
        } else {
                hs_len = 0;
        }

        if (likely(super)) {
                func->function.ss_descriptors = vla_ptr(vlabuf, d, ss_descs);
                ss_len = ffs_do_descs(ffs->ss_descs_count,
                                vla_ptr(vlabuf, d, raw_descs) + fs_len + hs_len,
                                d_raw_descs__sz - fs_len - hs_len,
                                __ffs_func_bind_do_descs, func);
                if (unlikely(ss_len < 0)) {
                        ret = ss_len;
                        goto error;
                }
        } else {
                ss_len = 0;
        }

        /*
         * Now handle interface numbers allocation and interface and
         * endpoint numbers rewriting.  We can do that in one go
         * now.
         */
        ret = ffs_do_descs(ffs->fs_descs_count +
                           (high ? ffs->hs_descs_count : 0) +
                           (super ? ffs->ss_descs_count : 0),
                           vla_ptr(vlabuf, d, raw_descs), d_raw_descs__sz,
                           __ffs_func_bind_do_nums, func);
        if (unlikely(ret < 0))
                goto error;

        func->function.os_desc_table = vla_ptr(vlabuf, d, os_desc_table);
        if (c->cdev->use_os_string) {
                for (i = 0; i < ffs->interfaces_count; ++i) {
                        struct usb_os_desc *desc;

                        desc = func->function.os_desc_table[i].os_desc =
                                vla_ptr(vlabuf, d, os_desc) +
                                i * sizeof(struct usb_os_desc);
                        desc->ext_compat_id =
                                vla_ptr(vlabuf, d, ext_compat) + i * 16;
                        INIT_LIST_HEAD(&desc->ext_prop);
                }
                ret = ffs_do_os_descs(ffs->ms_os_descs_count,
                                      vla_ptr(vlabuf, d, raw_descs) +
                                      fs_len + hs_len + ss_len,
                                      d_raw_descs__sz - fs_len - hs_len -
                                      ss_len,
                                      __ffs_func_bind_do_os_desc, func);
                if (unlikely(ret < 0))
                        goto error;
        }
        func->function.os_desc_n =
                c->cdev->use_os_string ? ffs->interfaces_count : 0;

        /* And we're done */
        ffs_event_add(ffs, FUNCTIONFS_BIND);
        return 0;

error:
        /* XXX Do we need to release all claimed endpoints here? */
        return ret;
}

static int ffs_func_bind(struct usb_configuration *c,
                         struct usb_function *f)
{
        struct f_fs_opts *ffs_opts = ffs_do_functionfs_bind(f, c);
        struct ffs_function *func = ffs_func_from_usb(f);
        int ret;

        if (IS_ERR(ffs_opts))
                return PTR_ERR(ffs_opts);

        ret = _ffs_func_bind(c, f);
        if (ret && !--ffs_opts->refcnt)
                functionfs_unbind(func->ffs);

        return ret;
}


/* Other USB function hooks *************************************************/

static void ffs_reset_work(struct work_struct *work)
{
        struct ffs_data *ffs = container_of(work,
                struct ffs_data, reset_work);
        ffs_data_reset(ffs);
}

static int ffs_func_set_alt(struct usb_function *f,
                            unsigned interface, unsigned alt)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;
        int ret = 0, intf;

        if (alt != (unsigned)-1) {
                intf = ffs_func_revmap_intf(func, interface);
                if (unlikely(intf < 0))
                        return intf;
        }

        if (ffs->func)
                ffs_func_eps_disable(ffs->func);

        if (ffs->state == FFS_DEACTIVATED) {
                ffs->state = FFS_CLOSING;
                INIT_WORK(&ffs->reset_work, ffs_reset_work);
                schedule_work(&ffs->reset_work);
                return -ENODEV;
        }

        if (ffs->state != FFS_ACTIVE)
                return -ENODEV;

        if (alt == (unsigned)-1) {
                ffs->func = NULL;
                ffs_event_add(ffs, FUNCTIONFS_DISABLE);
                return 0;
        }

        ffs->func = func;
        ret = ffs_func_eps_enable(func);
        if (likely(ret >= 0))
                ffs_event_add(ffs, FUNCTIONFS_ENABLE);
        return ret;
}

static void ffs_func_disable(struct usb_function *f)
{
        ffs_func_set_alt(f, 0, (unsigned)-1);
}

static int ffs_func_setup(struct usb_function *f,
                          const struct usb_ctrlrequest *creq)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;
        unsigned long flags;
        int ret;

        ENTER();

        pr_vdebug("creq->bRequestType = %02x\n", creq->bRequestType);
        pr_vdebug("creq->bRequest     = %02x\n", creq->bRequest);
        pr_vdebug("creq->wValue       = %04x\n", le16_to_cpu(creq->wValue));
        pr_vdebug("creq->wIndex       = %04x\n", le16_to_cpu(creq->wIndex));
        pr_vdebug("creq->wLength      = %04x\n", le16_to_cpu(creq->wLength));

        /*
         * Most requests directed to interface go through here
         * (notable exceptions are set/get interface) so we need to
         * handle them.  All other either handled by composite or
         * passed to usb_configuration->setup() (if one is set).  No
         * matter, we will handle requests directed to endpoint here
         * as well (as it's straightforward).  Other request recipient
         * types are only handled when the user flag FUNCTIONFS_ALL_CTRL_RECIP
         * is being used.
         */
        if (ffs->state != FFS_ACTIVE)
                return -ENODEV;

        switch (creq->bRequestType & USB_RECIP_MASK) {
        case USB_RECIP_INTERFACE:
                ret = ffs_func_revmap_intf(func, le16_to_cpu(creq->wIndex));
                if (unlikely(ret < 0))
                        return ret;
                break;

        case USB_RECIP_ENDPOINT:
                ret = ffs_func_revmap_ep(func, le16_to_cpu(creq->wIndex));
                if (unlikely(ret < 0))
                        return ret;
                if (func->ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
                        ret = func->ffs->eps_addrmap[ret];
                break;

        default:
                if (func->ffs->user_flags & FUNCTIONFS_ALL_CTRL_RECIP)
                        ret = le16_to_cpu(creq->wIndex);
                else
                        return -EOPNOTSUPP;
        }

        spin_lock_irqsave(&ffs->ev.waitq.lock, flags);
        ffs->ev.setup = *creq;
        ffs->ev.setup.wIndex = cpu_to_le16(ret);
        __ffs_event_add(ffs, FUNCTIONFS_SETUP);
        spin_unlock_irqrestore(&ffs->ev.waitq.lock, flags);

        return USB_GADGET_DELAYED_STATUS;
}

static bool ffs_func_req_match(struct usb_function *f,
                               const struct usb_ctrlrequest *creq,
                               bool config0)
{
        struct ffs_function *func = ffs_func_from_usb(f);

        if (config0 && !(func->ffs->user_flags & FUNCTIONFS_CONFIG0_SETUP))
                return false;

        switch (creq->bRequestType & USB_RECIP_MASK) {
        case USB_RECIP_INTERFACE:
                return (ffs_func_revmap_intf(func,
                                             le16_to_cpu(creq->wIndex)) >= 0);
        case USB_RECIP_ENDPOINT:
                return (ffs_func_revmap_ep(func,
                                           le16_to_cpu(creq->wIndex)) >= 0);
        default:
                return (bool) (func->ffs->user_flags &
                               FUNCTIONFS_ALL_CTRL_RECIP);
        }
}

static void ffs_func_suspend(struct usb_function *f)
{
        ENTER();
        ffs_event_add(ffs_func_from_usb(f)->ffs, FUNCTIONFS_SUSPEND);
}

static void ffs_func_resume(struct usb_function *f)
{
        ENTER();
        ffs_event_add(ffs_func_from_usb(f)->ffs, FUNCTIONFS_RESUME);
}


/* Endpoint and interface numbers reverse mapping ***************************/

static int ffs_func_revmap_ep(struct ffs_function *func, u8 num)
{
        num = func->eps_revmap[num & USB_ENDPOINT_NUMBER_MASK];
        return num ? num : -EDOM;
}

static int ffs_func_revmap_intf(struct ffs_function *func, u8 intf)
{
        short *nums = func->interfaces_nums;
        unsigned count = func->ffs->interfaces_count;

        for (; count; --count, ++nums) {
                if (*nums >= 0 && *nums == intf)
                        return nums - func->interfaces_nums;
        }

        return -EDOM;
}


/* Devices management *******************************************************/

static LIST_HEAD(ffs_devices);

static struct ffs_dev *_ffs_do_find_dev(const char *name)
{
        struct ffs_dev *dev;

        if (!name)
                return NULL;

        list_for_each_entry(dev, &ffs_devices, entry) {
                if (strcmp(dev->name, name) == 0)
                        return dev;
        }

        return NULL;
}

/*
 * ffs_lock must be taken by the caller of this function
 */
static struct ffs_dev *_ffs_get_single_dev(void)
{
        struct ffs_dev *dev;

        if (list_is_singular(&ffs_devices)) {
                dev = list_first_entry(&ffs_devices, struct ffs_dev, entry);
                if (dev->single)
                        return dev;
        }

        return NULL;
}

/*
 * ffs_lock must be taken by the caller of this function
 */
static struct ffs_dev *_ffs_find_dev(const char *name)
{
        struct ffs_dev *dev;

        dev = _ffs_get_single_dev();
        if (dev)
                return dev;

        return _ffs_do_find_dev(name);
}

/* Configfs support *********************************************************/

static inline struct f_fs_opts *to_ffs_opts(struct config_item *item)
{
        return container_of(to_config_group(item), struct f_fs_opts,
                            func_inst.group);
}

static void ffs_attr_release(struct config_item *item)
{
        struct f_fs_opts *opts = to_ffs_opts(item);

        usb_put_function_instance(&opts->func_inst);
}

static struct configfs_item_operations ffs_item_ops = {
        .release        = ffs_attr_release,
};

static const struct config_item_type ffs_func_type = {
        .ct_item_ops    = &ffs_item_ops,
        .ct_owner       = THIS_MODULE,
};


/* Function registration interface ******************************************/

static void ffs_free_inst(struct usb_function_instance *f)
{
        struct f_fs_opts *opts;

        opts = to_f_fs_opts(f);
        ffs_dev_lock();
        _ffs_free_dev(opts->dev);
        ffs_dev_unlock();
        kfree(opts);
}

static int ffs_set_inst_name(struct usb_function_instance *fi, const char *name)
{
        if (strlen(name) >= FIELD_SIZEOF(struct ffs_dev, name))
                return -ENAMETOOLONG;
        return ffs_name_dev(to_f_fs_opts(fi)->dev, name);
}

static struct usb_function_instance *ffs_alloc_inst(void)
{
        struct f_fs_opts *opts;
        struct ffs_dev *dev;

        opts = kzalloc(sizeof(*opts), GFP_KERNEL);
        if (!opts)
                return ERR_PTR(-ENOMEM);

        opts->func_inst.set_inst_name = ffs_set_inst_name;
        opts->func_inst.free_func_inst = ffs_free_inst;
        ffs_dev_lock();
        dev = _ffs_alloc_dev();
        ffs_dev_unlock();
        if (IS_ERR(dev)) {
                kfree(opts);
                return ERR_CAST(dev);
        }
        opts->dev = dev;
        dev->opts = opts;

        config_group_init_type_name(&opts->func_inst.group, "",
                                    &ffs_func_type);
        return &opts->func_inst;
}

static void ffs_free(struct usb_function *f)
{
        kfree(ffs_func_from_usb(f));
}

static void ffs_func_unbind(struct usb_configuration *c,
                            struct usb_function *f)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;
        struct f_fs_opts *opts =
                container_of(f->fi, struct f_fs_opts, func_inst);
        struct ffs_ep *ep = func->eps;
        unsigned count = ffs->eps_count;
        unsigned long flags;

        ENTER();
        if (ffs->func == func) {
                ffs_func_eps_disable(func);
                ffs->func = NULL;
        }

        if (!--opts->refcnt)
                functionfs_unbind(ffs);

        /* cleanup after autoconfig */
        spin_lock_irqsave(&func->ffs->eps_lock, flags);
        while (count--) {
                if (ep->ep && ep->req)
                        usb_ep_free_request(ep->ep, ep->req);
                ep->req = NULL;
                ++ep;
        }
        spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
        kfree(func->eps);
        func->eps = NULL;
        /*
         * eps, descriptors and interfaces_nums are allocated in the
         * same chunk so only one free is required.
         */
        func->function.fs_descriptors = NULL;
        func->function.hs_descriptors = NULL;
        func->function.ss_descriptors = NULL;
        func->interfaces_nums = NULL;

        ffs_event_add(ffs, FUNCTIONFS_UNBIND);
}

static struct usb_function *ffs_alloc(struct usb_function_instance *fi)
{
        struct ffs_function *func;

        ENTER();

        func = kzalloc(sizeof(*func), GFP_KERNEL);
        if (unlikely(!func))
                return ERR_PTR(-ENOMEM);

        func->function.name    = "Function FS Gadget";

        func->function.bind    = ffs_func_bind;
        func->function.unbind  = ffs_func_unbind;
        func->function.set_alt = ffs_func_set_alt;
        func->function.disable = ffs_func_disable;
        func->function.setup   = ffs_func_setup;
        func->function.req_match = ffs_func_req_match;
        func->function.suspend = ffs_func_suspend;
        func->function.resume  = ffs_func_resume;
        func->function.free_func = ffs_free;

        return &func->function;
}

/*
 * ffs_lock must be taken by the caller of this function
 */
static struct ffs_dev *_ffs_alloc_dev(void)
{
        struct ffs_dev *dev;
        int ret;

        if (_ffs_get_single_dev())
                        return ERR_PTR(-EBUSY);

        dev = kzalloc(sizeof(*dev), GFP_KERNEL);
        if (!dev)
                return ERR_PTR(-ENOMEM);

        if (list_empty(&ffs_devices)) {
                ret = functionfs_init();
                if (ret) {
                        kfree(dev);
                        return ERR_PTR(ret);
                }
        }

        list_add(&dev->entry, &ffs_devices);

        return dev;
}

int ffs_name_dev(struct ffs_dev *dev, const char *name)
{
        struct ffs_dev *existing;
        int ret = 0;

        ffs_dev_lock();

        existing = _ffs_do_find_dev(name);
        if (!existing)
                strlcpy(dev->name, name, ARRAY_SIZE(dev->name));
        else if (existing != dev)
                ret = -EBUSY;

        ffs_dev_unlock();

        return ret;
}
EXPORT_SYMBOL_GPL(ffs_name_dev);

int ffs_single_dev(struct ffs_dev *dev)
{
        int ret;

        ret = 0;
        ffs_dev_lock();

        if (!list_is_singular(&ffs_devices))
                ret = -EBUSY;
        else
                dev->single = true;

        ffs_dev_unlock();
        return ret;
}
EXPORT_SYMBOL_GPL(ffs_single_dev);

/*
 * ffs_lock must be taken by the caller of this function
 */
static void _ffs_free_dev(struct ffs_dev *dev)
{
        list_del(&dev->entry);

        /* Clear the private_data pointer to stop incorrect dev access */
        if (dev->ffs_data)
                dev->ffs_data->private_data = NULL;

        kfree(dev);
        if (list_empty(&ffs_devices))
                functionfs_cleanup();
}

static void *ffs_acquire_dev(const char *dev_name)
{
        struct ffs_dev *ffs_dev;

        ENTER();
        ffs_dev_lock();

        ffs_dev = _ffs_find_dev(dev_name);
        if (!ffs_dev)
                ffs_dev = ERR_PTR(-ENOENT);
        else if (ffs_dev->mounted)
                ffs_dev = ERR_PTR(-EBUSY);
        else if (ffs_dev->ffs_acquire_dev_callback &&
            ffs_dev->ffs_acquire_dev_callback(ffs_dev))
                ffs_dev = ERR_PTR(-ENOENT);
        else
                ffs_dev->mounted = true;

        ffs_dev_unlock();
        return ffs_dev;
}

static void ffs_release_dev(struct ffs_data *ffs_data)
{
        struct ffs_dev *ffs_dev;

        ENTER();
        ffs_dev_lock();

        ffs_dev = ffs_data->private_data;
        if (ffs_dev) {
                ffs_dev->mounted = false;

                if (ffs_dev->ffs_release_dev_callback)
                        ffs_dev->ffs_release_dev_callback(ffs_dev);
        }

        ffs_dev_unlock();
}

static int ffs_ready(struct ffs_data *ffs)
{
        struct ffs_dev *ffs_obj;
        int ret = 0;

        ENTER();
        ffs_dev_lock();

        ffs_obj = ffs->private_data;
        if (!ffs_obj) {
                ret = -EINVAL;
                goto done;
        }
        if (WARN_ON(ffs_obj->desc_ready)) {
                ret = -EBUSY;
                goto done;
        }

        ffs_obj->desc_ready = true;
        ffs_obj->ffs_data = ffs;

        if (ffs_obj->ffs_ready_callback) {
                ret = ffs_obj->ffs_ready_callback(ffs);
                if (ret)
                        goto done;
        }

        set_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags);
done:
        ffs_dev_unlock();
        return ret;
}

static void ffs_closed(struct ffs_data *ffs)
{
        struct ffs_dev *ffs_obj;
        struct f_fs_opts *opts;
        struct config_item *ci;

        ENTER();
        ffs_dev_lock();

        ffs_obj = ffs->private_data;
        if (!ffs_obj)
                goto done;

        ffs_obj->desc_ready = false;
        ffs_obj->ffs_data = NULL;

        if (test_and_clear_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags) &&
            ffs_obj->ffs_closed_callback)
                ffs_obj->ffs_closed_callback(ffs);

        if (ffs_obj->opts)
                opts = ffs_obj->opts;
        else
                goto done;

        if (opts->no_configfs || !opts->func_inst.group.cg_item.ci_parent
            || !kref_read(&opts->func_inst.group.cg_item.ci_kref))
                goto done;

        ci = opts->func_inst.group.cg_item.ci_parent->ci_parent;
        ffs_dev_unlock();

        if (test_bit(FFS_FL_BOUND, &ffs->flags))
                unregister_gadget_item(ci);
        return;
done:
        ffs_dev_unlock();
}

/* Misc helper functions ****************************************************/

static int ffs_mutex_lock(struct mutex *mutex, unsigned nonblock)
{
        return nonblock
                ? likely(mutex_trylock(mutex)) ? 0 : -EAGAIN
                : mutex_lock_interruptible(mutex);
}

static char *ffs_prepare_buffer(const char __user *buf, size_t len)
{
        char *data;

        if (unlikely(!len))
                return NULL;

        data = kmalloc(len, GFP_KERNEL);
        if (unlikely(!data))
                return ERR_PTR(-ENOMEM);

        if (unlikely(copy_from_user(data, buf, len))) {
                kfree(data);
                return ERR_PTR(-EFAULT);
        }

        pr_vdebug("Buffer from user space:\n");
        ffs_dump_mem("", data, len);

        return data;
}

DECLARE_USB_FUNCTION_INIT(ffs, ffs_alloc_inst, ffs_alloc);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Michal Nazarewicz");