xen: add xenfs to allow usermode <-> Xen interaction

[mirror_ubuntu-zesty-kernel.git] / drivers / xen / xenfs / xenbus.c

/*
 * Driver giving user-space access to the kernel's xenbus connection
 * to xenstore.
 *
 * Copyright (c) 2005, Christian Limpach
 * Copyright (c) 2005, Rusty Russell, IBM Corporation
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Changes:
 * 2008-10-07  Alex Zeffertt    Replaced /proc/xen/xenbus with xenfs filesystem
 *                              and /proc/xen compatibility mount point.
 *                              Turned xenfs into a loadable module.
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/uio.h>
#include <linux/notifier.h>
#include <linux/wait.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/uaccess.h>
#include <linux/init.h>
#include <linux/namei.h>
#include <linux/string.h>

#include "xenfs.h"
#include "../xenbus/xenbus_comms.h"

#include <xen/xenbus.h>
#include <asm/xen/hypervisor.h>

/*
 * An element of a list of outstanding transactions, for which we're
 * still waiting a reply.
 */
struct xenbus_transaction_holder {
        struct list_head list;
        struct xenbus_transaction handle;
};

/*
 * A buffer of data on the queue.
 */
struct read_buffer {
        struct list_head list;
        unsigned int cons;
        unsigned int len;
        char msg[];
};

struct xenbus_file_priv {
        /*
         * msgbuffer_mutex is held while partial requests are built up
         * and complete requests are acted on.  It therefore protects
         * the "transactions" and "watches" lists, and the partial
         * request length and buffer.
         *
         * reply_mutex protects the reply being built up to return to
         * usermode.  It nests inside msgbuffer_mutex but may be held
         * alone during a watch callback.
         */
        struct mutex msgbuffer_mutex;

        /* In-progress transactions */
        struct list_head transactions;

        /* Active watches. */
        struct list_head watches;

        /* Partial request. */
        unsigned int len;
        union {
                struct xsd_sockmsg msg;
                char buffer[PAGE_SIZE];
        } u;

        /* Response queue. */
        struct mutex reply_mutex;
        struct list_head read_buffers;
        wait_queue_head_t read_waitq;

};

/* Read out any raw xenbus messages queued up. */
static ssize_t xenbus_file_read(struct file *filp,
                               char __user *ubuf,
                               size_t len, loff_t *ppos)
{
        struct xenbus_file_priv *u = filp->private_data;
        struct read_buffer *rb;
        unsigned i;
        int ret;

        mutex_lock(&u->reply_mutex);
        while (list_empty(&u->read_buffers)) {
                mutex_unlock(&u->reply_mutex);
                ret = wait_event_interruptible(u->read_waitq,
                                               !list_empty(&u->read_buffers));
                if (ret)
                        return ret;
                mutex_lock(&u->reply_mutex);
        }

        rb = list_entry(u->read_buffers.next, struct read_buffer, list);
        i = 0;
        while (i < len) {
                unsigned sz = min((unsigned)len - i, rb->len - rb->cons);

                ret = copy_to_user(ubuf + i, &rb->msg[rb->cons], sz);

                i += sz - ret;
                rb->cons += sz - ret;

                if (ret != sz) {
                        if (i == 0)
                                i = -EFAULT;
                        goto out;
                }

                /* Clear out buffer if it has been consumed */
                if (rb->cons == rb->len) {
                        list_del(&rb->list);
                        kfree(rb);
                        if (list_empty(&u->read_buffers))
                                break;
                        rb = list_entry(u->read_buffers.next,
                                        struct read_buffer, list);
                }
        }

out:
        mutex_unlock(&u->reply_mutex);
        return i;
}

/*
 * Add a buffer to the queue.  Caller must hold the appropriate lock
 * if the queue is not local.  (Commonly the caller will build up
 * multiple queued buffers on a temporary local list, and then add it
 * to the appropriate list under lock once all the buffers have een
 * successfully allocated.)
 */
static int queue_reply(struct list_head *queue, const void *data, size_t len)
{
        struct read_buffer *rb;

        if (len == 0)
                return 0;

        rb = kmalloc(sizeof(*rb) + len, GFP_KERNEL);
        if (rb == NULL)
                return -ENOMEM;

        rb->cons = 0;
        rb->len = len;

        memcpy(rb->msg, data, len);

        list_add_tail(&rb->list, queue);
        return 0;
}

/*
 * Free all the read_buffer s on a list.
 * Caller must have sole reference to list.
 */
static void queue_cleanup(struct list_head *list)
{
        struct read_buffer *rb;

        while (!list_empty(list)) {
                rb = list_entry(list->next, struct read_buffer, list);
                list_del(list->next);
                kfree(rb);
        }
}

struct watch_adapter {
        struct list_head list;
        struct xenbus_watch watch;
        struct xenbus_file_priv *dev_data;
        char *token;
};

static void free_watch_adapter(struct watch_adapter *watch)
{
        kfree(watch->watch.node);
        kfree(watch->token);
        kfree(watch);
}

static struct watch_adapter *alloc_watch_adapter(const char *path,
                                                 const char *token)
{
        struct watch_adapter *watch;

        watch = kzalloc(sizeof(*watch), GFP_KERNEL);
        if (watch == NULL)
                goto out_fail;

        watch->watch.node = kstrdup(path, GFP_KERNEL);
        if (watch->watch.node == NULL)
                goto out_free;

        watch->token = kstrdup(token, GFP_KERNEL);
        if (watch->token == NULL)
                goto out_free;

        return watch;

out_free:
        free_watch_adapter(watch);

out_fail:
        return NULL;
}

static void watch_fired(struct xenbus_watch *watch,
                        const char **vec,
                        unsigned int len)
{
        struct watch_adapter *adap;
        struct xsd_sockmsg hdr;
        const char *path, *token;
        int path_len, tok_len, body_len, data_len = 0;
        int ret;
        LIST_HEAD(staging_q);

        adap = container_of(watch, struct watch_adapter, watch);

        path = vec[XS_WATCH_PATH];
        token = adap->token;

        path_len = strlen(path) + 1;
        tok_len = strlen(token) + 1;
        if (len > 2)
                data_len = vec[len] - vec[2] + 1;
        body_len = path_len + tok_len + data_len;

        hdr.type = XS_WATCH_EVENT;
        hdr.len = body_len;

        mutex_lock(&adap->dev_data->reply_mutex);

        ret = queue_reply(&staging_q, &hdr, sizeof(hdr));
        if (!ret)
                ret = queue_reply(&staging_q, path, path_len);
        if (!ret)
                ret = queue_reply(&staging_q, token, tok_len);
        if (!ret && len > 2)
                ret = queue_reply(&staging_q, vec[2], data_len);

        if (!ret) {
                /* success: pass reply list onto watcher */
                list_splice_tail(&staging_q, &adap->dev_data->read_buffers);
                wake_up(&adap->dev_data->read_waitq);
        } else
                queue_cleanup(&staging_q);

        mutex_unlock(&adap->dev_data->reply_mutex);
}

static int xenbus_write_transaction(unsigned msg_type,
                                    struct xenbus_file_priv *u)
{
        int rc, ret;
        void *reply;
        struct xenbus_transaction_holder *trans = NULL;
        LIST_HEAD(staging_q);

        if (msg_type == XS_TRANSACTION_START) {
                trans = kmalloc(sizeof(*trans), GFP_KERNEL);
                if (!trans) {
                        rc = -ENOMEM;
                        goto out;
                }
        }

        reply = xenbus_dev_request_and_reply(&u->u.msg);
        if (IS_ERR(reply)) {
                kfree(trans);
                rc = PTR_ERR(reply);
                goto out;
        }

        if (msg_type == XS_TRANSACTION_START) {
                trans->handle.id = simple_strtoul(reply, NULL, 0);

                list_add(&trans->list, &u->transactions);
        } else if (msg_type == XS_TRANSACTION_END) {
                list_for_each_entry(trans, &u->transactions, list)
                        if (trans->handle.id == u->u.msg.tx_id)
                                break;
                BUG_ON(&trans->list == &u->transactions);
                list_del(&trans->list);

                kfree(trans);
        }

        mutex_lock(&u->reply_mutex);
        ret = queue_reply(&staging_q, &u->u.msg, sizeof(u->u.msg));
        if (!ret)
                ret = queue_reply(&staging_q, reply, u->u.msg.len);
        if (!ret) {
                list_splice_tail(&staging_q, &u->read_buffers);
                wake_up(&u->read_waitq);
        } else {
                queue_cleanup(&staging_q);
                rc = ret;
        }
        mutex_unlock(&u->reply_mutex);

        kfree(reply);

out:
        return rc;
}

static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u)
{
        struct watch_adapter *watch, *tmp_watch;
        char *path, *token;
        int err, rc;
        LIST_HEAD(staging_q);

        path = u->u.buffer + sizeof(u->u.msg);
        token = memchr(path, 0, u->u.msg.len);
        if (token == NULL) {
                rc = -EILSEQ;
                goto out;
        }
        token++;

        if (msg_type == XS_WATCH) {
                watch = alloc_watch_adapter(path, token);
                if (watch == NULL) {
                        rc = -ENOMEM;
                        goto out;
                }

                watch->watch.callback = watch_fired;
                watch->dev_data = u;

                err = register_xenbus_watch(&watch->watch);
                if (err) {
                        free_watch_adapter(watch);
                        rc = err;
                        goto out;
                }
                list_add(&watch->list, &u->watches);
        } else {
                list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
                        if (!strcmp(watch->token, token) &&
                            !strcmp(watch->watch.node, path)) {
                                unregister_xenbus_watch(&watch->watch);
                                list_del(&watch->list);
                                free_watch_adapter(watch);
                                break;
                        }
                }
        }

        /* Success.  Synthesize a reply to say all is OK. */
        {
                struct {
                        struct xsd_sockmsg hdr;
                        char body[3];
                } __packed reply = {
                        {
                                .type = msg_type,
                                .len = sizeof(reply.body)
                        },
                        "OK"
                };

                mutex_lock(&u->reply_mutex);
                rc = queue_reply(&u->read_buffers, &reply, sizeof(reply));
                mutex_unlock(&u->reply_mutex);
        }

out:
        return rc;
}

static ssize_t xenbus_file_write(struct file *filp,
                                const char __user *ubuf,
                                size_t len, loff_t *ppos)
{
        struct xenbus_file_priv *u = filp->private_data;
        uint32_t msg_type;
        int rc = len;
        int ret;
        LIST_HEAD(staging_q);

        /*
         * We're expecting usermode to be writing properly formed
         * xenbus messages.  If they write an incomplete message we
         * buffer it up.  Once it is complete, we act on it.
         */

        /*
         * Make sure concurrent writers can't stomp all over each
         * other's messages and make a mess of our partial message
         * buffer.  We don't make any attemppt to stop multiple
         * writers from making a mess of each other's incomplete
         * messages; we're just trying to guarantee our own internal
         * consistency and make sure that single writes are handled
         * atomically.
         */
        mutex_lock(&u->msgbuffer_mutex);

        /* Get this out of the way early to avoid confusion */
        if (len == 0)
                goto out;

        /* Can't write a xenbus message larger we can buffer */
        if ((len + u->len) > sizeof(u->u.buffer)) {
                /* On error, dump existing buffer */
                u->len = 0;
                rc = -EINVAL;
                goto out;
        }

        ret = copy_from_user(u->u.buffer + u->len, ubuf, len);

        if (ret == len) {
                rc = -EFAULT;
                goto out;
        }

        /* Deal with a partial copy. */
        len -= ret;
        rc = len;

        u->len += len;

        /* Return if we haven't got a full message yet */
        if (u->len < sizeof(u->u.msg))
                goto out;       /* not even the header yet */

        /* If we're expecting a message that's larger than we can
           possibly send, dump what we have and return an error. */
        if ((sizeof(u->u.msg) + u->u.msg.len) > sizeof(u->u.buffer)) {
                rc = -E2BIG;
                u->len = 0;
                goto out;
        }

        if (u->len < (sizeof(u->u.msg) + u->u.msg.len))
                goto out;       /* incomplete data portion */

        /*
         * OK, now we have a complete message.  Do something with it.
         */

        msg_type = u->u.msg.type;

        switch (msg_type) {
        case XS_TRANSACTION_START:
        case XS_TRANSACTION_END:
        case XS_DIRECTORY:
        case XS_READ:
        case XS_GET_PERMS:
        case XS_RELEASE:
        case XS_GET_DOMAIN_PATH:
        case XS_WRITE:
        case XS_MKDIR:
        case XS_RM:
        case XS_SET_PERMS:
                /* Send out a transaction */
                ret = xenbus_write_transaction(msg_type, u);
                break;

        case XS_WATCH:
        case XS_UNWATCH:
                /* (Un)Ask for some path to be watched for changes */
                ret = xenbus_write_watch(msg_type, u);
                break;

        default:
                ret = -EINVAL;
                break;
        }
        if (ret != 0)
                rc = ret;

        /* Buffered message consumed */
        u->len = 0;

 out:
        mutex_unlock(&u->msgbuffer_mutex);
        return rc;
}

static int xenbus_file_open(struct inode *inode, struct file *filp)
{
        struct xenbus_file_priv *u;

        if (xen_store_evtchn == 0)
                return -ENOENT;

        nonseekable_open(inode, filp);

        u = kzalloc(sizeof(*u), GFP_KERNEL);
        if (u == NULL)
                return -ENOMEM;

        INIT_LIST_HEAD(&u->transactions);
        INIT_LIST_HEAD(&u->watches);
        INIT_LIST_HEAD(&u->read_buffers);
        init_waitqueue_head(&u->read_waitq);

        mutex_init(&u->reply_mutex);
        mutex_init(&u->msgbuffer_mutex);

        filp->private_data = u;

        return 0;
}

static int xenbus_file_release(struct inode *inode, struct file *filp)
{
        struct xenbus_file_priv *u = filp->private_data;
        struct xenbus_transaction_holder *trans, *tmp;
        struct watch_adapter *watch, *tmp_watch;

        /*
         * No need for locking here because there are no other users,
         * by definition.
         */

        list_for_each_entry_safe(trans, tmp, &u->transactions, list) {
                xenbus_transaction_end(trans->handle, 1);
                list_del(&trans->list);
                kfree(trans);
        }

        list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
                unregister_xenbus_watch(&watch->watch);
                list_del(&watch->list);
                free_watch_adapter(watch);
        }

        kfree(u);

        return 0;
}

static unsigned int xenbus_file_poll(struct file *file, poll_table *wait)
{
        struct xenbus_file_priv *u = file->private_data;

        poll_wait(file, &u->read_waitq, wait);
        if (!list_empty(&u->read_buffers))
                return POLLIN | POLLRDNORM;
        return 0;
}

const struct file_operations xenbus_file_ops = {
        .read = xenbus_file_read,
        .write = xenbus_file_write,
        .open = xenbus_file_open,
        .release = xenbus_file_release,
        .poll = xenbus_file_poll,
};