inotify_user.c

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/*
 * fs/inotify_user.c - inotify support for userspace
 *
 * Authors:
 *  John McCutchan  <[email protected]>
 *  Robert Love <[email protected]>
 *
 * 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 <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 = -EINTR;
        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_fasync(int fd, struct file *file, int on)
{
    struct fsnotify_group *group = file->private_data;

    return fasync_helper(fd, file, on, &group->inotify_data.fa) >= 0 ? 0 : -EIO;
}

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);

    fsnotify_clear_marks_by_group(group);

    /* free this group, matching get was inotify_init->fsnotify_obtain_group */
    fsnotify_put_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 = {
    .poll       = inotify_poll,
    .read       = inotify_read,
    .fasync     = inotify_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;

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

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

    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;

    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 */
    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.fa = NULL;
    group->inotify_data.user = get_current_user();

    if (atomic_inc_return(&group->inotify_data.user->inotify_devs) >
        inotify_max_user_instances) {
        fsnotify_put_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_put_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);

    /* 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);