Merge branch 'x86/header-guards' into x86-v28-for-linus-phase1

[mirror_ubuntu-zesty-kernel.git] / fs / pipe.c

/*
 *  linux/fs/pipe.c
 *
 *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
 */

#include <linux/mm.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/pipe_fs_i.h>
#include <linux/uio.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/audit.h>
#include <linux/syscalls.h>

#include <asm/uaccess.h>
#include <asm/ioctls.h>

/*
 * We use a start+len construction, which provides full use of the 
 * allocated memory.
 * -- Florian Coosmann (FGC)
 * 
 * Reads with count = 0 should always return 0.
 * -- Julian Bradfield 1999-06-07.
 *
 * FIFOs and Pipes now generate SIGIO for both readers and writers.
 * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
 *
 * pipe_read & write cleanup
 * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
 */

/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct pipe_inode_info *pipe)
{
        DEFINE_WAIT(wait);

        /*
         * Pipes are system-local resources, so sleeping on them
         * is considered a noninteractive wait:
         */
        prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
        if (pipe->inode)
                mutex_unlock(&pipe->inode->i_mutex);
        schedule();
        finish_wait(&pipe->wait, &wait);
        if (pipe->inode)
                mutex_lock(&pipe->inode->i_mutex);
}

static int
pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len,
                        int atomic)
{
        unsigned long copy;

        while (len > 0) {
                while (!iov->iov_len)
                        iov++;
                copy = min_t(unsigned long, len, iov->iov_len);

                if (atomic) {
                        if (__copy_from_user_inatomic(to, iov->iov_base, copy))
                                return -EFAULT;
                } else {
                        if (copy_from_user(to, iov->iov_base, copy))
                                return -EFAULT;
                }
                to += copy;
                len -= copy;
                iov->iov_base += copy;
                iov->iov_len -= copy;
        }
        return 0;
}

static int
pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len,
                      int atomic)
{
        unsigned long copy;

        while (len > 0) {
                while (!iov->iov_len)
                        iov++;
                copy = min_t(unsigned long, len, iov->iov_len);

                if (atomic) {
                        if (__copy_to_user_inatomic(iov->iov_base, from, copy))
                                return -EFAULT;
                } else {
                        if (copy_to_user(iov->iov_base, from, copy))
                                return -EFAULT;
                }
                from += copy;
                len -= copy;
                iov->iov_base += copy;
                iov->iov_len -= copy;
        }
        return 0;
}

/*
 * Attempt to pre-fault in the user memory, so we can use atomic copies.
 * Returns the number of bytes not faulted in.
 */
static int iov_fault_in_pages_write(struct iovec *iov, unsigned long len)
{
        while (!iov->iov_len)
                iov++;

        while (len > 0) {
                unsigned long this_len;

                this_len = min_t(unsigned long, len, iov->iov_len);
                if (fault_in_pages_writeable(iov->iov_base, this_len))
                        break;

                len -= this_len;
                iov++;
        }

        return len;
}

/*
 * Pre-fault in the user memory, so we can use atomic copies.
 */
static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
{
        while (!iov->iov_len)
                iov++;

        while (len > 0) {
                unsigned long this_len;

                this_len = min_t(unsigned long, len, iov->iov_len);
                fault_in_pages_readable(iov->iov_base, this_len);
                len -= this_len;
                iov++;
        }
}

static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
                                  struct pipe_buffer *buf)
{
        struct page *page = buf->page;

        /*
         * If nobody else uses this page, and we don't already have a
         * temporary page, let's keep track of it as a one-deep
         * allocation cache. (Otherwise just release our reference to it)
         */
        if (page_count(page) == 1 && !pipe->tmp_page)
                pipe->tmp_page = page;
        else
                page_cache_release(page);
}

/**
 * generic_pipe_buf_map - virtually map a pipe buffer
 * @pipe:       the pipe that the buffer belongs to
 * @buf:        the buffer that should be mapped
 * @atomic:     whether to use an atomic map
 *
 * Description:
 *      This function returns a kernel virtual address mapping for the
 *      pipe_buffer passed in @buf. If @atomic is set, an atomic map is provided
 *      and the caller has to be careful not to fault before calling
 *      the unmap function.
 *
 *      Note that this function occupies KM_USER0 if @atomic != 0.
 */
void *generic_pipe_buf_map(struct pipe_inode_info *pipe,
                           struct pipe_buffer *buf, int atomic)
{
        if (atomic) {
                buf->flags |= PIPE_BUF_FLAG_ATOMIC;
                return kmap_atomic(buf->page, KM_USER0);
        }

        return kmap(buf->page);
}

/**
 * generic_pipe_buf_unmap - unmap a previously mapped pipe buffer
 * @pipe:       the pipe that the buffer belongs to
 * @buf:        the buffer that should be unmapped
 * @map_data:   the data that the mapping function returned
 *
 * Description:
 *      This function undoes the mapping that ->map() provided.
 */
void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
                            struct pipe_buffer *buf, void *map_data)
{
        if (buf->flags & PIPE_BUF_FLAG_ATOMIC) {
                buf->flags &= ~PIPE_BUF_FLAG_ATOMIC;
                kunmap_atomic(map_data, KM_USER0);
        } else
                kunmap(buf->page);
}

/**
 * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer
 * @pipe:       the pipe that the buffer belongs to
 * @buf:        the buffer to attempt to steal
 *
 * Description:
 *      This function attempts to steal the &struct page attached to
 *      @buf. If successful, this function returns 0 and returns with
 *      the page locked. The caller may then reuse the page for whatever
 *      he wishes; the typical use is insertion into a different file
 *      page cache.
 */
int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
                           struct pipe_buffer *buf)
{
        struct page *page = buf->page;

        /*
         * A reference of one is golden, that means that the owner of this
         * page is the only one holding a reference to it. lock the page
         * and return OK.
         */
        if (page_count(page) == 1) {
                lock_page(page);
                return 0;
        }

        return 1;
}

/**
 * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
 * @pipe:       the pipe that the buffer belongs to
 * @buf:        the buffer to get a reference to
 *
 * Description:
 *      This function grabs an extra reference to @buf. It's used in
 *      in the tee() system call, when we duplicate the buffers in one
 *      pipe into another.
 */
void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
{
        page_cache_get(buf->page);
}

/**
 * generic_pipe_buf_confirm - verify contents of the pipe buffer
 * @info:       the pipe that the buffer belongs to
 * @buf:        the buffer to confirm
 *
 * Description:
 *      This function does nothing, because the generic pipe code uses
 *      pages that are always good when inserted into the pipe.
 */
int generic_pipe_buf_confirm(struct pipe_inode_info *info,
                             struct pipe_buffer *buf)
{
        return 0;
}

static const struct pipe_buf_operations anon_pipe_buf_ops = {
        .can_merge = 1,
        .map = generic_pipe_buf_map,
        .unmap = generic_pipe_buf_unmap,
        .confirm = generic_pipe_buf_confirm,
        .release = anon_pipe_buf_release,
        .steal = generic_pipe_buf_steal,
        .get = generic_pipe_buf_get,
};

static ssize_t
pipe_read(struct kiocb *iocb, const struct iovec *_iov,
           unsigned long nr_segs, loff_t pos)
{
        struct file *filp = iocb->ki_filp;
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct pipe_inode_info *pipe;
        int do_wakeup;
        ssize_t ret;
        struct iovec *iov = (struct iovec *)_iov;
        size_t total_len;

        total_len = iov_length(iov, nr_segs);
        /* Null read succeeds. */
        if (unlikely(total_len == 0))
                return 0;

        do_wakeup = 0;
        ret = 0;
        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;
        for (;;) {
                int bufs = pipe->nrbufs;
                if (bufs) {
                        int curbuf = pipe->curbuf;
                        struct pipe_buffer *buf = pipe->bufs + curbuf;
                        const struct pipe_buf_operations *ops = buf->ops;
                        void *addr;
                        size_t chars = buf->len;
                        int error, atomic;

                        if (chars > total_len)
                                chars = total_len;

                        error = ops->confirm(pipe, buf);
                        if (error) {
                                if (!ret)
                                        error = ret;
                                break;
                        }

                        atomic = !iov_fault_in_pages_write(iov, chars);
redo:
                        addr = ops->map(pipe, buf, atomic);
                        error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars, atomic);
                        ops->unmap(pipe, buf, addr);
                        if (unlikely(error)) {
                                /*
                                 * Just retry with the slow path if we failed.
                                 */
                                if (atomic) {
                                        atomic = 0;
                                        goto redo;
                                }
                                if (!ret)
                                        ret = error;
                                break;
                        }
                        ret += chars;
                        buf->offset += chars;
                        buf->len -= chars;
                        if (!buf->len) {
                                buf->ops = NULL;
                                ops->release(pipe, buf);
                                curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
                                pipe->curbuf = curbuf;
                                pipe->nrbufs = --bufs;
                                do_wakeup = 1;
                        }
                        total_len -= chars;
                        if (!total_len)
                                break;  /* common path: read succeeded */
                }
                if (bufs)       /* More to do? */
                        continue;
                if (!pipe->writers)
                        break;
                if (!pipe->waiting_writers) {
                        /* syscall merging: Usually we must not sleep
                         * if O_NONBLOCK is set, or if we got some data.
                         * But if a writer sleeps in kernel space, then
                         * we can wait for that data without violating POSIX.
                         */
                        if (ret)
                                break;
                        if (filp->f_flags & O_NONBLOCK) {
                                ret = -EAGAIN;
                                break;
                        }
                }
                if (signal_pending(current)) {
                        if (!ret)
                                ret = -ERESTARTSYS;
                        break;
                }
                if (do_wakeup) {
                        wake_up_interruptible_sync(&pipe->wait);
                        kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
                }
                pipe_wait(pipe);
        }
        mutex_unlock(&inode->i_mutex);

        /* Signal writers asynchronously that there is more room. */
        if (do_wakeup) {
                wake_up_interruptible_sync(&pipe->wait);
                kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
        }
        if (ret > 0)
                file_accessed(filp);
        return ret;
}

static ssize_t
pipe_write(struct kiocb *iocb, const struct iovec *_iov,
            unsigned long nr_segs, loff_t ppos)
{
        struct file *filp = iocb->ki_filp;
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct pipe_inode_info *pipe;
        ssize_t ret;
        int do_wakeup;
        struct iovec *iov = (struct iovec *)_iov;
        size_t total_len;
        ssize_t chars;

        total_len = iov_length(iov, nr_segs);
        /* Null write succeeds. */
        if (unlikely(total_len == 0))
                return 0;

        do_wakeup = 0;
        ret = 0;
        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;

        if (!pipe->readers) {
                send_sig(SIGPIPE, current, 0);
                ret = -EPIPE;
                goto out;
        }

        /* We try to merge small writes */
        chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
        if (pipe->nrbufs && chars != 0) {
                int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &
                                                        (PIPE_BUFFERS-1);
                struct pipe_buffer *buf = pipe->bufs + lastbuf;
                const struct pipe_buf_operations *ops = buf->ops;
                int offset = buf->offset + buf->len;

                if (ops->can_merge && offset + chars <= PAGE_SIZE) {
                        int error, atomic = 1;
                        void *addr;

                        error = ops->confirm(pipe, buf);
                        if (error)
                                goto out;

                        iov_fault_in_pages_read(iov, chars);
redo1:
                        addr = ops->map(pipe, buf, atomic);
                        error = pipe_iov_copy_from_user(offset + addr, iov,
                                                        chars, atomic);
                        ops->unmap(pipe, buf, addr);
                        ret = error;
                        do_wakeup = 1;
                        if (error) {
                                if (atomic) {
                                        atomic = 0;
                                        goto redo1;
                                }
                                goto out;
                        }
                        buf->len += chars;
                        total_len -= chars;
                        ret = chars;
                        if (!total_len)
                                goto out;
                }
        }

        for (;;) {
                int bufs;

                if (!pipe->readers) {
                        send_sig(SIGPIPE, current, 0);
                        if (!ret)
                                ret = -EPIPE;
                        break;
                }
                bufs = pipe->nrbufs;
                if (bufs < PIPE_BUFFERS) {
                        int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS-1);
                        struct pipe_buffer *buf = pipe->bufs + newbuf;
                        struct page *page = pipe->tmp_page;
                        char *src;
                        int error, atomic = 1;

                        if (!page) {
                                page = alloc_page(GFP_HIGHUSER);
                                if (unlikely(!page)) {
                                        ret = ret ? : -ENOMEM;
                                        break;
                                }
                                pipe->tmp_page = page;
                        }
                        /* Always wake up, even if the copy fails. Otherwise
                         * we lock up (O_NONBLOCK-)readers that sleep due to
                         * syscall merging.
                         * FIXME! Is this really true?
                         */
                        do_wakeup = 1;
                        chars = PAGE_SIZE;
                        if (chars > total_len)
                                chars = total_len;

                        iov_fault_in_pages_read(iov, chars);
redo2:
                        if (atomic)
                                src = kmap_atomic(page, KM_USER0);
                        else
                                src = kmap(page);

                        error = pipe_iov_copy_from_user(src, iov, chars,
                                                        atomic);
                        if (atomic)
                                kunmap_atomic(src, KM_USER0);
                        else
                                kunmap(page);

                        if (unlikely(error)) {
                                if (atomic) {
                                        atomic = 0;
                                        goto redo2;
                                }
                                if (!ret)
                                        ret = error;
                                break;
                        }
                        ret += chars;

                        /* Insert it into the buffer array */
                        buf->page = page;
                        buf->ops = &anon_pipe_buf_ops;
                        buf->offset = 0;
                        buf->len = chars;
                        pipe->nrbufs = ++bufs;
                        pipe->tmp_page = NULL;

                        total_len -= chars;
                        if (!total_len)
                                break;
                }
                if (bufs < PIPE_BUFFERS)
                        continue;
                if (filp->f_flags & O_NONBLOCK) {
                        if (!ret)
                                ret = -EAGAIN;
                        break;
                }
                if (signal_pending(current)) {
                        if (!ret)
                                ret = -ERESTARTSYS;
                        break;
                }
                if (do_wakeup) {
                        wake_up_interruptible_sync(&pipe->wait);
                        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                        do_wakeup = 0;
                }
                pipe->waiting_writers++;
                pipe_wait(pipe);
                pipe->waiting_writers--;
        }
out:
        mutex_unlock(&inode->i_mutex);
        if (do_wakeup) {
                wake_up_interruptible_sync(&pipe->wait);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
        }
        if (ret > 0)
                file_update_time(filp);
        return ret;
}

static ssize_t
bad_pipe_r(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
        return -EBADF;
}

static ssize_t
bad_pipe_w(struct file *filp, const char __user *buf, size_t count,
           loff_t *ppos)
{
        return -EBADF;
}

static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct pipe_inode_info *pipe;
        int count, buf, nrbufs;

        switch (cmd) {
                case FIONREAD:
                        mutex_lock(&inode->i_mutex);
                        pipe = inode->i_pipe;
                        count = 0;
                        buf = pipe->curbuf;
                        nrbufs = pipe->nrbufs;
                        while (--nrbufs >= 0) {
                                count += pipe->bufs[buf].len;
                                buf = (buf+1) & (PIPE_BUFFERS-1);
                        }
                        mutex_unlock(&inode->i_mutex);

                        return put_user(count, (int __user *)arg);
                default:
                        return -EINVAL;
        }
}

/* No kernel lock held - fine */
static unsigned int
pipe_poll(struct file *filp, poll_table *wait)
{
        unsigned int mask;
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct pipe_inode_info *pipe = inode->i_pipe;
        int nrbufs;

        poll_wait(filp, &pipe->wait, wait);

        /* Reading only -- no need for acquiring the semaphore.  */
        nrbufs = pipe->nrbufs;
        mask = 0;
        if (filp->f_mode & FMODE_READ) {
                mask = (nrbufs > 0) ? POLLIN | POLLRDNORM : 0;
                if (!pipe->writers && filp->f_version != pipe->w_counter)
                        mask |= POLLHUP;
        }

        if (filp->f_mode & FMODE_WRITE) {
                mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
                /*
                 * Most Unices do not set POLLERR for FIFOs but on Linux they
                 * behave exactly like pipes for poll().
                 */
                if (!pipe->readers)
                        mask |= POLLERR;
        }

        return mask;
}

static int
pipe_release(struct inode *inode, int decr, int decw)
{
        struct pipe_inode_info *pipe;

        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;
        pipe->readers -= decr;
        pipe->writers -= decw;

        if (!pipe->readers && !pipe->writers) {
                free_pipe_info(inode);
        } else {
                wake_up_interruptible_sync(&pipe->wait);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
        }
        mutex_unlock(&inode->i_mutex);

        return 0;
}

static int
pipe_read_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        int retval;

        mutex_lock(&inode->i_mutex);
        retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_readers);
        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}


static int
pipe_write_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        int retval;

        mutex_lock(&inode->i_mutex);
        retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_writers);
        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}


static int
pipe_rdwr_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct pipe_inode_info *pipe = inode->i_pipe;
        int retval;

        mutex_lock(&inode->i_mutex);

        retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);

        if (retval >= 0)
                retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);

        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}


static int
pipe_read_release(struct inode *inode, struct file *filp)
{
        pipe_read_fasync(-1, filp, 0);
        return pipe_release(inode, 1, 0);
}

static int
pipe_write_release(struct inode *inode, struct file *filp)
{
        pipe_write_fasync(-1, filp, 0);
        return pipe_release(inode, 0, 1);
}

static int
pipe_rdwr_release(struct inode *inode, struct file *filp)
{
        int decr, decw;

        pipe_rdwr_fasync(-1, filp, 0);
        decr = (filp->f_mode & FMODE_READ) != 0;
        decw = (filp->f_mode & FMODE_WRITE) != 0;
        return pipe_release(inode, decr, decw);
}

static int
pipe_read_open(struct inode *inode, struct file *filp)
{
        /* We could have perhaps used atomic_t, but this and friends
           below are the only places.  So it doesn't seem worthwhile.  */
        mutex_lock(&inode->i_mutex);
        inode->i_pipe->readers++;
        mutex_unlock(&inode->i_mutex);

        return 0;
}

static int
pipe_write_open(struct inode *inode, struct file *filp)
{
        mutex_lock(&inode->i_mutex);
        inode->i_pipe->writers++;
        mutex_unlock(&inode->i_mutex);

        return 0;
}

static int
pipe_rdwr_open(struct inode *inode, struct file *filp)
{
        mutex_lock(&inode->i_mutex);
        if (filp->f_mode & FMODE_READ)
                inode->i_pipe->readers++;
        if (filp->f_mode & FMODE_WRITE)
                inode->i_pipe->writers++;
        mutex_unlock(&inode->i_mutex);

        return 0;
}

/*
 * The file_operations structs are not static because they
 * are also used in linux/fs/fifo.c to do operations on FIFOs.
 *
 * Pipes reuse fifos' file_operations structs.
 */
const struct file_operations read_pipefifo_fops = {
        .llseek         = no_llseek,
        .read           = do_sync_read,
        .aio_read       = pipe_read,
        .write          = bad_pipe_w,
        .poll           = pipe_poll,
        .unlocked_ioctl = pipe_ioctl,
        .open           = pipe_read_open,
        .release        = pipe_read_release,
        .fasync         = pipe_read_fasync,
};

const struct file_operations write_pipefifo_fops = {
        .llseek         = no_llseek,
        .read           = bad_pipe_r,
        .write          = do_sync_write,
        .aio_write      = pipe_write,
        .poll           = pipe_poll,
        .unlocked_ioctl = pipe_ioctl,
        .open           = pipe_write_open,
        .release        = pipe_write_release,
        .fasync         = pipe_write_fasync,
};

const struct file_operations rdwr_pipefifo_fops = {
        .llseek         = no_llseek,
        .read           = do_sync_read,
        .aio_read       = pipe_read,
        .write          = do_sync_write,
        .aio_write      = pipe_write,
        .poll           = pipe_poll,
        .unlocked_ioctl = pipe_ioctl,
        .open           = pipe_rdwr_open,
        .release        = pipe_rdwr_release,
        .fasync         = pipe_rdwr_fasync,
};

struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
{
        struct pipe_inode_info *pipe;

        pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
        if (pipe) {
                init_waitqueue_head(&pipe->wait);
                pipe->r_counter = pipe->w_counter = 1;
                pipe->inode = inode;
        }

        return pipe;
}

void __free_pipe_info(struct pipe_inode_info *pipe)
{
        int i;

        for (i = 0; i < PIPE_BUFFERS; i++) {
                struct pipe_buffer *buf = pipe->bufs + i;
                if (buf->ops)
                        buf->ops->release(pipe, buf);
        }
        if (pipe->tmp_page)
                __free_page(pipe->tmp_page);
        kfree(pipe);
}

void free_pipe_info(struct inode *inode)
{
        __free_pipe_info(inode->i_pipe);
        inode->i_pipe = NULL;
}

static struct vfsmount *pipe_mnt __read_mostly;
static int pipefs_delete_dentry(struct dentry *dentry)
{
        /*
         * At creation time, we pretended this dentry was hashed
         * (by clearing DCACHE_UNHASHED bit in d_flags)
         * At delete time, we restore the truth : not hashed.
         * (so that dput() can proceed correctly)
         */
        dentry->d_flags |= DCACHE_UNHASHED;
        return 0;
}

/*
 * pipefs_dname() is called from d_path().
 */
static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
        return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
                                dentry->d_inode->i_ino);
}

static struct dentry_operations pipefs_dentry_operations = {
        .d_delete       = pipefs_delete_dentry,
        .d_dname        = pipefs_dname,
};

static struct inode * get_pipe_inode(void)
{
        struct inode *inode = new_inode(pipe_mnt->mnt_sb);
        struct pipe_inode_info *pipe;

        if (!inode)
                goto fail_inode;

        pipe = alloc_pipe_info(inode);
        if (!pipe)
                goto fail_iput;
        inode->i_pipe = pipe;

        pipe->readers = pipe->writers = 1;
        inode->i_fop = &rdwr_pipefifo_fops;

        /*
         * Mark the inode dirty from the very beginning,
         * that way it will never be moved to the dirty
         * list because "mark_inode_dirty()" will think
         * that it already _is_ on the dirty list.
         */
        inode->i_state = I_DIRTY;
        inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
        inode->i_uid = current->fsuid;
        inode->i_gid = current->fsgid;
        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;

        return inode;

fail_iput:
        iput(inode);

fail_inode:
        return NULL;
}

struct file *create_write_pipe(int flags)
{
        int err;
        struct inode *inode;
        struct file *f;
        struct dentry *dentry;
        struct qstr name = { .name = "" };

        err = -ENFILE;
        inode = get_pipe_inode();
        if (!inode)
                goto err;

        err = -ENOMEM;
        dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);
        if (!dentry)
                goto err_inode;

        dentry->d_op = &pipefs_dentry_operations;
        /*
         * We dont want to publish this dentry into global dentry hash table.
         * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
         * This permits a working /proc/$pid/fd/XXX on pipes
         */
        dentry->d_flags &= ~DCACHE_UNHASHED;
        d_instantiate(dentry, inode);

        err = -ENFILE;
        f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipefifo_fops);
        if (!f)
                goto err_dentry;
        f->f_mapping = inode->i_mapping;

        f->f_flags = O_WRONLY | (flags & O_NONBLOCK);
        f->f_version = 0;

        return f;

 err_dentry:
        free_pipe_info(inode);
        dput(dentry);
        return ERR_PTR(err);

 err_inode:
        free_pipe_info(inode);
        iput(inode);
 err:
        return ERR_PTR(err);
}

void free_write_pipe(struct file *f)
{
        free_pipe_info(f->f_dentry->d_inode);
        path_put(&f->f_path);
        put_filp(f);
}

struct file *create_read_pipe(struct file *wrf, int flags)
{
        struct file *f = get_empty_filp();
        if (!f)
                return ERR_PTR(-ENFILE);

        /* Grab pipe from the writer */
        f->f_path = wrf->f_path;
        path_get(&wrf->f_path);
        f->f_mapping = wrf->f_path.dentry->d_inode->i_mapping;

        f->f_pos = 0;
        f->f_flags = O_RDONLY | (flags & O_NONBLOCK);
        f->f_op = &read_pipefifo_fops;
        f->f_mode = FMODE_READ;
        f->f_version = 0;

        return f;
}

int do_pipe_flags(int *fd, int flags)
{
        struct file *fw, *fr;
        int error;
        int fdw, fdr;

        if (flags & ~(O_CLOEXEC | O_NONBLOCK))
                return -EINVAL;

        fw = create_write_pipe(flags);
        if (IS_ERR(fw))
                return PTR_ERR(fw);
        fr = create_read_pipe(fw, flags);
        error = PTR_ERR(fr);
        if (IS_ERR(fr))
                goto err_write_pipe;

        error = get_unused_fd_flags(flags);
        if (error < 0)
                goto err_read_pipe;
        fdr = error;

        error = get_unused_fd_flags(flags);
        if (error < 0)
                goto err_fdr;
        fdw = error;

        error = audit_fd_pair(fdr, fdw);
        if (error < 0)
                goto err_fdw;

        fd_install(fdr, fr);
        fd_install(fdw, fw);
        fd[0] = fdr;
        fd[1] = fdw;

        return 0;

 err_fdw:
        put_unused_fd(fdw);
 err_fdr:
        put_unused_fd(fdr);
 err_read_pipe:
        path_put(&fr->f_path);
        put_filp(fr);
 err_write_pipe:
        free_write_pipe(fw);
        return error;
}

int do_pipe(int *fd)
{
        return do_pipe_flags(fd, 0);
}

/*
 * sys_pipe() is the normal C calling standard for creating
 * a pipe. It's not the way Unix traditionally does this, though.
 */
asmlinkage long __weak sys_pipe2(int __user *fildes, int flags)
{
        int fd[2];
        int error;

        error = do_pipe_flags(fd, flags);
        if (!error) {
                if (copy_to_user(fildes, fd, sizeof(fd))) {
                        sys_close(fd[0]);
                        sys_close(fd[1]);
                        error = -EFAULT;
                }
        }
        return error;
}

asmlinkage long __weak sys_pipe(int __user *fildes)
{
        return sys_pipe2(fildes, 0);
}

/*
 * pipefs should _never_ be mounted by userland - too much of security hassle,
 * no real gain from having the whole whorehouse mounted. So we don't need
 * any operations on the root directory. However, we need a non-trivial
 * d_name - pipe: will go nicely and kill the special-casing in procfs.
 */
static int pipefs_get_sb(struct file_system_type *fs_type,
                         int flags, const char *dev_name, void *data,
                         struct vfsmount *mnt)
{
        return get_sb_pseudo(fs_type, "pipe:", NULL, PIPEFS_MAGIC, mnt);
}

static struct file_system_type pipe_fs_type = {
        .name           = "pipefs",
        .get_sb         = pipefs_get_sb,
        .kill_sb        = kill_anon_super,
};

static int __init init_pipe_fs(void)
{
        int err = register_filesystem(&pipe_fs_type);

        if (!err) {
                pipe_mnt = kern_mount(&pipe_fs_type);
                if (IS_ERR(pipe_mnt)) {
                        err = PTR_ERR(pipe_mnt);
                        unregister_filesystem(&pipe_fs_type);
                }
        }
        return err;
}

static void __exit exit_pipe_fs(void)
{
        unregister_filesystem(&pipe_fs_type);
        mntput(pipe_mnt);
}

fs_initcall(init_pipe_fs);
module_exit(exit_pipe_fs);