Merge branch 'for-next' of git://git.infradead.org/users/eparis/notify

[mirror_ubuntu-zesty-kernel.git] / fs / notify / inotify / inotify_user.c

/*
 * fs/inotify_user.c - inotify support for userspace
 *
 * Authors:
 *      John McCutchan  <ttb@tentacle.dhs.org>
 *      Robert Love     <rml@novell.com>
 *
 * Copyright (C) 2005 John McCutchan
 * Copyright 2006 Hewlett-Packard Development Company, L.P.
 *
 * Copyright (C) 2009 Eric Paris <Red Hat Inc>
 * inotify was largely rewriten to make use of the fsnotify infrastructure
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2, or (at your option) any
 * later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

#include <linux/file.h>
#include <linux/fs.h> /* struct inode */
#include <linux/fsnotify_backend.h>
#include <linux/idr.h>
#include <linux/init.h> /* module_init */
#include <linux/inotify.h>
#include <linux/kernel.h> /* roundup() */
#include <linux/namei.h> /* LOOKUP_FOLLOW */
#include <linux/sched.h> /* struct user */
#include <linux/slab.h> /* struct kmem_cache */
#include <linux/syscalls.h>
#include <linux/types.h>
#include <linux/anon_inodes.h>
#include <linux/uaccess.h>
#include <linux/poll.h>
#include <linux/wait.h>

#include "inotify.h"
#include "../fdinfo.h"

#include <asm/ioctls.h>

/* these are configurable via /proc/sys/fs/inotify/ */
static int inotify_max_user_instances __read_mostly;
static int inotify_max_queued_events __read_mostly;
static int inotify_max_user_watches __read_mostly;

static struct kmem_cache *inotify_inode_mark_cachep __read_mostly;
struct kmem_cache *event_priv_cachep __read_mostly;

#ifdef CONFIG_SYSCTL

#include <linux/sysctl.h>

static int zero;

ctl_table inotify_table[] = {
        {
                .procname       = "max_user_instances",
                .data           = &inotify_max_user_instances,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &zero,
        },
        {
                .procname       = "max_user_watches",
                .data           = &inotify_max_user_watches,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &zero,
        },
        {
                .procname       = "max_queued_events",
                .data           = &inotify_max_queued_events,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &zero
        },
        { }
};
#endif /* CONFIG_SYSCTL */

static inline __u32 inotify_arg_to_mask(u32 arg)
{
        __u32 mask;

        /*
         * everything should accept their own ignored, cares about children,
         * and should receive events when the inode is unmounted
         */
        mask = (FS_IN_IGNORED | FS_EVENT_ON_CHILD | FS_UNMOUNT);

        /* mask off the flags used to open the fd */
        mask |= (arg & (IN_ALL_EVENTS | IN_ONESHOT | IN_EXCL_UNLINK));

        return mask;
}

static inline u32 inotify_mask_to_arg(__u32 mask)
{
        return mask & (IN_ALL_EVENTS | IN_ISDIR | IN_UNMOUNT | IN_IGNORED |
                       IN_Q_OVERFLOW);
}

/* intofiy userspace file descriptor functions */
static unsigned int inotify_poll(struct file *file, poll_table *wait)
{
        struct fsnotify_group *group = file->private_data;
        int ret = 0;

        poll_wait(file, &group->notification_waitq, wait);
        mutex_lock(&group->notification_mutex);
        if (!fsnotify_notify_queue_is_empty(group))
                ret = POLLIN | POLLRDNORM;
        mutex_unlock(&group->notification_mutex);

        return ret;
}

/*
 * Get an inotify_kernel_event if one exists and is small
 * enough to fit in "count". Return an error pointer if
 * not large enough.
 *
 * Called with the group->notification_mutex held.
 */
static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
                                            size_t count)
{
        size_t event_size = sizeof(struct inotify_event);
        struct fsnotify_event *event;

        if (fsnotify_notify_queue_is_empty(group))
                return NULL;

        event = fsnotify_peek_notify_event(group);

        pr_debug("%s: group=%p event=%p\n", __func__, group, event);

        if (event->name_len)
                event_size += roundup(event->name_len + 1, event_size);

        if (event_size > count)
                return ERR_PTR(-EINVAL);

        /* held the notification_mutex the whole time, so this is the
         * same event we peeked above */
        fsnotify_remove_notify_event(group);

        return event;
}

/*
 * Copy an event to user space, returning how much we copied.
 *
 * We already checked that the event size is smaller than the
 * buffer we had in "get_one_event()" above.
 */
static ssize_t copy_event_to_user(struct fsnotify_group *group,
                                  struct fsnotify_event *event,
                                  char __user *buf)
{
        struct inotify_event inotify_event;
        struct fsnotify_event_private_data *fsn_priv;
        struct inotify_event_private_data *priv;
        size_t event_size = sizeof(struct inotify_event);
        size_t name_len = 0;

        pr_debug("%s: group=%p event=%p\n", __func__, group, event);

        /* we get the inotify watch descriptor from the event private data */
        spin_lock(&event->lock);
        fsn_priv = fsnotify_remove_priv_from_event(group, event);
        spin_unlock(&event->lock);

        if (!fsn_priv)
                inotify_event.wd = -1;
        else {
                priv = container_of(fsn_priv, struct inotify_event_private_data,
                                    fsnotify_event_priv_data);
                inotify_event.wd = priv->wd;
                inotify_free_event_priv(fsn_priv);
        }

        /*
         * round up event->name_len so it is a multiple of event_size
         * plus an extra byte for the terminating '\0'.
         */
        if (event->name_len)
                name_len = roundup(event->name_len + 1, event_size);
        inotify_event.len = name_len;

        inotify_event.mask = inotify_mask_to_arg(event->mask);
        inotify_event.cookie = event->sync_cookie;

        /* send the main event */
        if (copy_to_user(buf, &inotify_event, event_size))
                return -EFAULT;

        buf += event_size;

        /*
         * fsnotify only stores the pathname, so here we have to send the pathname
         * and then pad that pathname out to a multiple of sizeof(inotify_event)
         * with zeros.  I get my zeros from the nul_inotify_event.
         */
        if (name_len) {
                unsigned int len_to_zero = name_len - event->name_len;
                /* copy the path name */
                if (copy_to_user(buf, event->file_name, event->name_len))
                        return -EFAULT;
                buf += event->name_len;

                /* fill userspace with 0's */
                if (clear_user(buf, len_to_zero))
                        return -EFAULT;
                buf += len_to_zero;
                event_size += name_len;
        }

        return event_size;
}

static ssize_t inotify_read(struct file *file, char __user *buf,
                            size_t count, loff_t *pos)
{
        struct fsnotify_group *group;
        struct fsnotify_event *kevent;
        char __user *start;
        int ret;
        DEFINE_WAIT(wait);

        start = buf;
        group = file->private_data;

        while (1) {
                prepare_to_wait(&group->notification_waitq, &wait, TASK_INTERRUPTIBLE);

                mutex_lock(&group->notification_mutex);
                kevent = get_one_event(group, count);
                mutex_unlock(&group->notification_mutex);

                pr_debug("%s: group=%p kevent=%p\n", __func__, group, kevent);

                if (kevent) {
                        ret = PTR_ERR(kevent);
                        if (IS_ERR(kevent))
                                break;
                        ret = copy_event_to_user(group, kevent, buf);
                        fsnotify_put_event(kevent);
                        if (ret < 0)
                                break;
                        buf += ret;
                        count -= ret;
                        continue;
                }

                ret = -EAGAIN;
                if (file->f_flags & O_NONBLOCK)
                        break;
                ret = -ERESTARTSYS;
                if (signal_pending(current))
                        break;

                if (start != buf)
                        break;

                schedule();
        }

        finish_wait(&group->notification_waitq, &wait);
        if (start != buf && ret != -EFAULT)
                ret = buf - start;
        return ret;
}

static int inotify_release(struct inode *ignored, struct file *file)
{
        struct fsnotify_group *group = file->private_data;

        pr_debug("%s: group=%p\n", __func__, group);

        if (file->f_flags & FASYNC)
                fsnotify_fasync(-1, file, 0);

        /* free this group, matching get was inotify_init->fsnotify_obtain_group */
        fsnotify_destroy_group(group);

        return 0;
}

static long inotify_ioctl(struct file *file, unsigned int cmd,
                          unsigned long arg)
{
        struct fsnotify_group *group;
        struct fsnotify_event_holder *holder;
        struct fsnotify_event *event;
        void __user *p;
        int ret = -ENOTTY;
        size_t send_len = 0;

        group = file->private_data;
        p = (void __user *) arg;

        pr_debug("%s: group=%p cmd=%u\n", __func__, group, cmd);

        switch (cmd) {
        case FIONREAD:
                mutex_lock(&group->notification_mutex);
                list_for_each_entry(holder, &group->notification_list, event_list) {
                        event = holder->event;
                        send_len += sizeof(struct inotify_event);
                        if (event->name_len)
                                send_len += roundup(event->name_len + 1,
                                                sizeof(struct inotify_event));
                }
                mutex_unlock(&group->notification_mutex);
                ret = put_user(send_len, (int __user *) p);
                break;
        }

        return ret;
}

static const struct file_operations inotify_fops = {
        .show_fdinfo    = inotify_show_fdinfo,
        .poll           = inotify_poll,
        .read           = inotify_read,
        .fasync         = fsnotify_fasync,
        .release        = inotify_release,
        .unlocked_ioctl = inotify_ioctl,
        .compat_ioctl   = inotify_ioctl,
        .llseek         = noop_llseek,
};


/*
 * find_inode - resolve a user-given path to a specific inode
 */
static int inotify_find_inode(const char __user *dirname, struct path *path, unsigned flags)
{
        int error;

        error = user_path_at(AT_FDCWD, dirname, flags, path);
        if (error)
                return error;
        /* you can only watch an inode if you have read permissions on it */
        error = inode_permission(path->dentry->d_inode, MAY_READ);
        if (error)
                path_put(path);
        return error;
}

static int inotify_add_to_idr(struct idr *idr, spinlock_t *idr_lock,
                              int *last_wd,
                              struct inotify_inode_mark *i_mark)
{
        int ret;

        do {
                if (unlikely(!idr_pre_get(idr, GFP_KERNEL)))
                        return -ENOMEM;

                spin_lock(idr_lock);
                ret = idr_get_new_above(idr, i_mark, *last_wd + 1,
                                        &i_mark->wd);
                /* we added the mark to the idr, take a reference */
                if (!ret) {
                        *last_wd = i_mark->wd;
                        fsnotify_get_mark(&i_mark->fsn_mark);
                }
                spin_unlock(idr_lock);
        } while (ret == -EAGAIN);

        return ret;
}

static struct inotify_inode_mark *inotify_idr_find_locked(struct fsnotify_group *group,
                                                                int wd)
{
        struct idr *idr = &group->inotify_data.idr;
        spinlock_t *idr_lock = &group->inotify_data.idr_lock;
        struct inotify_inode_mark *i_mark;

        assert_spin_locked(idr_lock);

        i_mark = idr_find(idr, wd);
        if (i_mark) {
                struct fsnotify_mark *fsn_mark = &i_mark->fsn_mark;

                fsnotify_get_mark(fsn_mark);
                /* One ref for being in the idr, one ref we just took */
                BUG_ON(atomic_read(&fsn_mark->refcnt) < 2);
        }

        return i_mark;
}

static struct inotify_inode_mark *inotify_idr_find(struct fsnotify_group *group,
                                                         int wd)
{
        struct inotify_inode_mark *i_mark;
        spinlock_t *idr_lock = &group->inotify_data.idr_lock;

        spin_lock(idr_lock);
        i_mark = inotify_idr_find_locked(group, wd);
        spin_unlock(idr_lock);

        return i_mark;
}

static void do_inotify_remove_from_idr(struct fsnotify_group *group,
                                       struct inotify_inode_mark *i_mark)
{
        struct idr *idr = &group->inotify_data.idr;
        spinlock_t *idr_lock = &group->inotify_data.idr_lock;
        int wd = i_mark->wd;

        assert_spin_locked(idr_lock);

        idr_remove(idr, wd);

        /* removed from the idr, drop that ref */
        fsnotify_put_mark(&i_mark->fsn_mark);
}

/*
 * Remove the mark from the idr (if present) and drop the reference
 * on the mark because it was in the idr.
 */
static void inotify_remove_from_idr(struct fsnotify_group *group,
                                    struct inotify_inode_mark *i_mark)
{
        spinlock_t *idr_lock = &group->inotify_data.idr_lock;
        struct inotify_inode_mark *found_i_mark = NULL;
        int wd;

        spin_lock(idr_lock);
        wd = i_mark->wd;

        /*
         * does this i_mark think it is in the idr?  we shouldn't get called
         * if it wasn't....
         */
        if (wd == -1) {
                WARN_ONCE(1, "%s: i_mark=%p i_mark->wd=%d i_mark->group=%p"
                        " i_mark->inode=%p\n", __func__, i_mark, i_mark->wd,
                        i_mark->fsn_mark.group, i_mark->fsn_mark.i.inode);
                goto out;
        }

        /* Lets look in the idr to see if we find it */
        found_i_mark = inotify_idr_find_locked(group, wd);
        if (unlikely(!found_i_mark)) {
                WARN_ONCE(1, "%s: i_mark=%p i_mark->wd=%d i_mark->group=%p"
                        " i_mark->inode=%p\n", __func__, i_mark, i_mark->wd,
                        i_mark->fsn_mark.group, i_mark->fsn_mark.i.inode);
                goto out;
        }

        /*
         * We found an mark in the idr at the right wd, but it's
         * not the mark we were told to remove.  eparis seriously
         * fucked up somewhere.
         */
        if (unlikely(found_i_mark != i_mark)) {
                WARN_ONCE(1, "%s: i_mark=%p i_mark->wd=%d i_mark->group=%p "
                        "mark->inode=%p found_i_mark=%p found_i_mark->wd=%d "
                        "found_i_mark->group=%p found_i_mark->inode=%p\n",
                        __func__, i_mark, i_mark->wd, i_mark->fsn_mark.group,
                        i_mark->fsn_mark.i.inode, found_i_mark, found_i_mark->wd,
                        found_i_mark->fsn_mark.group,
                        found_i_mark->fsn_mark.i.inode);
                goto out;
        }

        /*
         * One ref for being in the idr
         * one ref held by the caller trying to kill us
         * one ref grabbed by inotify_idr_find
         */
        if (unlikely(atomic_read(&i_mark->fsn_mark.refcnt) < 3)) {
                printk(KERN_ERR "%s: i_mark=%p i_mark->wd=%d i_mark->group=%p"
                        " i_mark->inode=%p\n", __func__, i_mark, i_mark->wd,
                        i_mark->fsn_mark.group, i_mark->fsn_mark.i.inode);
                /* we can't really recover with bad ref cnting.. */
                BUG();
        }

        do_inotify_remove_from_idr(group, i_mark);
out:
        /* match the ref taken by inotify_idr_find_locked() */
        if (found_i_mark)
                fsnotify_put_mark(&found_i_mark->fsn_mark);
        i_mark->wd = -1;
        spin_unlock(idr_lock);
}

/*
 * Send IN_IGNORED for this wd, remove this wd from the idr.
 */
void inotify_ignored_and_remove_idr(struct fsnotify_mark *fsn_mark,
                                    struct fsnotify_group *group)
{
        struct inotify_inode_mark *i_mark;
        struct fsnotify_event *ignored_event, *notify_event;
        struct inotify_event_private_data *event_priv;
        struct fsnotify_event_private_data *fsn_event_priv;
        int ret;

        i_mark = container_of(fsn_mark, struct inotify_inode_mark, fsn_mark);

        ignored_event = fsnotify_create_event(NULL, FS_IN_IGNORED, NULL,
                                              FSNOTIFY_EVENT_NONE, NULL, 0,
                                              GFP_NOFS);
        if (!ignored_event)
                goto skip_send_ignore;

        event_priv = kmem_cache_alloc(event_priv_cachep, GFP_NOFS);
        if (unlikely(!event_priv))
                goto skip_send_ignore;

        fsn_event_priv = &event_priv->fsnotify_event_priv_data;

        fsnotify_get_group(group);
        fsn_event_priv->group = group;
        event_priv->wd = i_mark->wd;

        notify_event = fsnotify_add_notify_event(group, ignored_event, fsn_event_priv, NULL);
        if (notify_event) {
                if (IS_ERR(notify_event))
                        ret = PTR_ERR(notify_event);
                else
                        fsnotify_put_event(notify_event);
                inotify_free_event_priv(fsn_event_priv);
        }

skip_send_ignore:
        /* matches the reference taken when the event was created */
        if (ignored_event)
                fsnotify_put_event(ignored_event);

        /* remove this mark from the idr */
        inotify_remove_from_idr(group, i_mark);

        atomic_dec(&group->inotify_data.user->inotify_watches);
}

/* ding dong the mark is dead */
static void inotify_free_mark(struct fsnotify_mark *fsn_mark)
{
        struct inotify_inode_mark *i_mark;

        i_mark = container_of(fsn_mark, struct inotify_inode_mark, fsn_mark);

        kmem_cache_free(inotify_inode_mark_cachep, i_mark);
}

static int inotify_update_existing_watch(struct fsnotify_group *group,
                                         struct inode *inode,
                                         u32 arg)
{
        struct fsnotify_mark *fsn_mark;
        struct inotify_inode_mark *i_mark;
        __u32 old_mask, new_mask;
        __u32 mask;
        int add = (arg & IN_MASK_ADD);
        int ret;

        /* don't allow invalid bits: we don't want flags set */
        mask = inotify_arg_to_mask(arg);
        if (unlikely(!(mask & IN_ALL_EVENTS)))
                return -EINVAL;

        fsn_mark = fsnotify_find_inode_mark(group, inode);
        if (!fsn_mark)
                return -ENOENT;

        i_mark = container_of(fsn_mark, struct inotify_inode_mark, fsn_mark);

        spin_lock(&fsn_mark->lock);

        old_mask = fsn_mark->mask;
        if (add)
                fsnotify_set_mark_mask_locked(fsn_mark, (fsn_mark->mask | mask));
        else
                fsnotify_set_mark_mask_locked(fsn_mark, mask);
        new_mask = fsn_mark->mask;

        spin_unlock(&fsn_mark->lock);

        if (old_mask != new_mask) {
                /* more bits in old than in new? */
                int dropped = (old_mask & ~new_mask);
                /* more bits in this fsn_mark than the inode's mask? */
                int do_inode = (new_mask & ~inode->i_fsnotify_mask);

                /* update the inode with this new fsn_mark */
                if (dropped || do_inode)
                        fsnotify_recalc_inode_mask(inode);

        }

        /* return the wd */
        ret = i_mark->wd;

        /* match the get from fsnotify_find_mark() */
        fsnotify_put_mark(fsn_mark);

        return ret;
}

static int inotify_new_watch(struct fsnotify_group *group,
                             struct inode *inode,
                             u32 arg)
{
        struct inotify_inode_mark *tmp_i_mark;
        __u32 mask;
        int ret;
        struct idr *idr = &group->inotify_data.idr;
        spinlock_t *idr_lock = &group->inotify_data.idr_lock;

        /* don't allow invalid bits: we don't want flags set */
        mask = inotify_arg_to_mask(arg);
        if (unlikely(!(mask & IN_ALL_EVENTS)))
                return -EINVAL;

        tmp_i_mark = kmem_cache_alloc(inotify_inode_mark_cachep, GFP_KERNEL);
        if (unlikely(!tmp_i_mark))
                return -ENOMEM;

        fsnotify_init_mark(&tmp_i_mark->fsn_mark, inotify_free_mark);
        tmp_i_mark->fsn_mark.mask = mask;
        tmp_i_mark->wd = -1;

        ret = -ENOSPC;
        if (atomic_read(&group->inotify_data.user->inotify_watches) >= inotify_max_user_watches)
                goto out_err;

        ret = inotify_add_to_idr(idr, idr_lock, &group->inotify_data.last_wd,
                                 tmp_i_mark);
        if (ret)
                goto out_err;

        /* we are on the idr, now get on the inode */
        ret = fsnotify_add_mark(&tmp_i_mark->fsn_mark, group, inode, NULL, 0);
        if (ret) {
                /* we failed to get on the inode, get off the idr */
                inotify_remove_from_idr(group, tmp_i_mark);
                goto out_err;
        }

        /* increment the number of watches the user has */
        atomic_inc(&group->inotify_data.user->inotify_watches);

        /* return the watch descriptor for this new mark */
        ret = tmp_i_mark->wd;

out_err:
        /* match the ref from fsnotify_init_mark() */
        fsnotify_put_mark(&tmp_i_mark->fsn_mark);

        return ret;
}

static int inotify_update_watch(struct fsnotify_group *group, struct inode *inode, u32 arg)
{
        int ret = 0;

retry:
        /* try to update and existing watch with the new arg */
        ret = inotify_update_existing_watch(group, inode, arg);
        /* no mark present, try to add a new one */
        if (ret == -ENOENT)
                ret = inotify_new_watch(group, inode, arg);
        /*
         * inotify_new_watch could race with another thread which did an
         * inotify_new_watch between the update_existing and the add watch
         * here, go back and try to update an existing mark again.
         */
        if (ret == -EEXIST)
                goto retry;

        return ret;
}

static struct fsnotify_group *inotify_new_group(unsigned int max_events)
{
        struct fsnotify_group *group;

        group = fsnotify_alloc_group(&inotify_fsnotify_ops);
        if (IS_ERR(group))
                return group;

        group->max_events = max_events;

        spin_lock_init(&group->inotify_data.idr_lock);
        idr_init(&group->inotify_data.idr);
        group->inotify_data.last_wd = 0;
        group->inotify_data.user = get_current_user();

        if (atomic_inc_return(&group->inotify_data.user->inotify_devs) >
            inotify_max_user_instances) {
                fsnotify_destroy_group(group);
                return ERR_PTR(-EMFILE);
        }

        return group;
}


/* inotify syscalls */
SYSCALL_DEFINE1(inotify_init1, int, flags)
{
        struct fsnotify_group *group;
        int ret;

        /* Check the IN_* constants for consistency.  */
        BUILD_BUG_ON(IN_CLOEXEC != O_CLOEXEC);
        BUILD_BUG_ON(IN_NONBLOCK != O_NONBLOCK);

        if (flags & ~(IN_CLOEXEC | IN_NONBLOCK))
                return -EINVAL;

        /* fsnotify_obtain_group took a reference to group, we put this when we kill the file in the end */
        group = inotify_new_group(inotify_max_queued_events);
        if (IS_ERR(group))
                return PTR_ERR(group);

        ret = anon_inode_getfd("inotify", &inotify_fops, group,
                                  O_RDONLY | flags);
        if (ret < 0)
                fsnotify_destroy_group(group);

        return ret;
}

SYSCALL_DEFINE0(inotify_init)
{
        return sys_inotify_init1(0);
}

SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname,
                u32, mask)
{
        struct fsnotify_group *group;
        struct inode *inode;
        struct path path;
        struct fd f;
        int ret;
        unsigned flags = 0;

        f = fdget(fd);
        if (unlikely(!f.file))
                return -EBADF;

        /* verify that this is indeed an inotify instance */
        if (unlikely(f.file->f_op != &inotify_fops)) {
                ret = -EINVAL;
                goto fput_and_out;
        }

        if (!(mask & IN_DONT_FOLLOW))
                flags |= LOOKUP_FOLLOW;
        if (mask & IN_ONLYDIR)
                flags |= LOOKUP_DIRECTORY;

        ret = inotify_find_inode(pathname, &path, flags);
        if (ret)
                goto fput_and_out;

        /* inode held in place by reference to path; group by fget on fd */
        inode = path.dentry->d_inode;
        group = f.file->private_data;

        /* create/update an inode mark */
        ret = inotify_update_watch(group, inode, mask);
        path_put(&path);
fput_and_out:
        fdput(f);
        return ret;
}

SYSCALL_DEFINE2(inotify_rm_watch, int, fd, __s32, wd)
{
        struct fsnotify_group *group;
        struct inotify_inode_mark *i_mark;
        struct fd f;
        int ret = 0;

        f = fdget(fd);
        if (unlikely(!f.file))
                return -EBADF;

        /* verify that this is indeed an inotify instance */
        ret = -EINVAL;
        if (unlikely(f.file->f_op != &inotify_fops))
                goto out;

        group = f.file->private_data;

        ret = -EINVAL;
        i_mark = inotify_idr_find(group, wd);
        if (unlikely(!i_mark))
                goto out;

        ret = 0;

        fsnotify_destroy_mark(&i_mark->fsn_mark, group);

        /* match ref taken by inotify_idr_find */
        fsnotify_put_mark(&i_mark->fsn_mark);

out:
        fdput(f);
        return ret;
}

/*
 * inotify_user_setup - Our initialization function.  Note that we cannot return
 * error because we have compiled-in VFS hooks.  So an (unlikely) failure here
 * must result in panic().
 */
static int __init inotify_user_setup(void)
{
        BUILD_BUG_ON(IN_ACCESS != FS_ACCESS);
        BUILD_BUG_ON(IN_MODIFY != FS_MODIFY);
        BUILD_BUG_ON(IN_ATTRIB != FS_ATTRIB);
        BUILD_BUG_ON(IN_CLOSE_WRITE != FS_CLOSE_WRITE);
        BUILD_BUG_ON(IN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
        BUILD_BUG_ON(IN_OPEN != FS_OPEN);
        BUILD_BUG_ON(IN_MOVED_FROM != FS_MOVED_FROM);
        BUILD_BUG_ON(IN_MOVED_TO != FS_MOVED_TO);
        BUILD_BUG_ON(IN_CREATE != FS_CREATE);
        BUILD_BUG_ON(IN_DELETE != FS_DELETE);
        BUILD_BUG_ON(IN_DELETE_SELF != FS_DELETE_SELF);
        BUILD_BUG_ON(IN_MOVE_SELF != FS_MOVE_SELF);
        BUILD_BUG_ON(IN_UNMOUNT != FS_UNMOUNT);
        BUILD_BUG_ON(IN_Q_OVERFLOW != FS_Q_OVERFLOW);
        BUILD_BUG_ON(IN_IGNORED != FS_IN_IGNORED);
        BUILD_BUG_ON(IN_EXCL_UNLINK != FS_EXCL_UNLINK);
        BUILD_BUG_ON(IN_ISDIR != FS_ISDIR);
        BUILD_BUG_ON(IN_ONESHOT != FS_IN_ONESHOT);

        BUG_ON(hweight32(ALL_INOTIFY_BITS) != 21);

        inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark, SLAB_PANIC);
        event_priv_cachep = KMEM_CACHE(inotify_event_private_data, SLAB_PANIC);

        inotify_max_queued_events = 16384;
        inotify_max_user_instances = 128;
        inotify_max_user_watches = 8192;

        return 0;
}
module_init(inotify_user_setup);