On Tue, Nov 06, 2007 at 02:33:53AM -0800, akpm@linux-foundation.org wrote:

[mmotm.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/magic.h> /* superblock magic number */
#include <linux/mount.h> /* mntget */
#include <linux/namei.h> /* LOOKUP_FOLLOW */
#include <linux/path.h> /* struct path */
#include <linux/sched.h> /* struct user */
#include <linux/slab.h> /* struct kmem_cache */
#include <linux/syscalls.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/poll.h>
#include <linux/wait.h>

#include "inotify.h"

#include <asm/ioctls.h>

static struct vfsmount *inotify_mnt __read_mostly;

/* these are configurable via /proc/sys/fs/inotify/ */
static int inotify_max_user_instances __read_mostly;
static int inotify_max_queued_events __read_mostly;
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[] = {
        {
                .ctl_name       = INOTIFY_MAX_USER_INSTANCES,
                .procname       = "max_user_instances",
                .data           = &inotify_max_user_instances,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = &proc_dointvec_minmax,
                .strategy       = &sysctl_intvec,
                .extra1         = &zero,
        },
        {
                .ctl_name       = INOTIFY_MAX_USER_WATCHES,
                .procname       = "max_user_watches",
                .data           = &inotify_max_user_watches,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = &proc_dointvec_minmax,
                .strategy       = &sysctl_intvec,
                .extra1         = &zero,
        },
        {
                .ctl_name       = INOTIFY_MAX_QUEUED_EVENTS,
                .procname       = "max_queued_events",
                .data           = &inotify_max_queued_events,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = &proc_dointvec_minmax,
                .strategy       = &sysctl_intvec,
                .extra1         = &zero
        },
        { .ctl_name = 0 }
};
#endif /* CONFIG_SYSCTL */

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

        /* everything should accept their own ignored and cares about children */
        mask = (FS_IN_IGNORED | FS_EVENT_ON_CHILD);

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

        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);

        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;

        /* 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);

                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;
        struct user_struct *user = group->inotify_data.user;

        fsnotify_clear_marks_by_group(group);

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

        atomic_dec(&user->inotify_devs);

        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;

        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,
};


/*
 * 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_entry *ientry)
{
        int ret;

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

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

        return ret;
}

static struct inotify_inode_mark_entry *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_entry *ientry;

        assert_spin_locked(idr_lock);

        ientry = idr_find(idr, wd);
        if (ientry) {
                struct fsnotify_mark_entry *fsn_entry = &ientry->fsn_entry;

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

        return ientry;
}

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

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

        return ientry;
}

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

        assert_spin_locked(idr_lock);

        idr_remove(idr, wd);

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

/*
 * 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_entry *ientry)
{
        spinlock_t *idr_lock = &group->inotify_data.idr_lock;
        struct inotify_inode_mark_entry *found_ientry = NULL;
        int wd;

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

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

        /* Lets look in the idr to see if we find it */
        found_ientry = inotify_idr_find_locked(group, wd);
        if (unlikely(!found_ientry)) {
                printk(KERN_WARNING "%s: ientry=%p ientry->wd=%d ientry->group=%p"
                        " ientry->inode=%p\n", __func__, ientry, ientry->wd,
                        ientry->fsn_entry.group, ientry->fsn_entry.inode);
                WARN_ON(1);
                goto out;
        }

        /*
         * We found an entry in the idr at the right wd, but it's
         * not the entry we were told to remove.  eparis seriously
         * fucked up somewhere.
         */
        if (unlikely(found_ientry != ientry)) {
                WARN_ON(1);
                printk(KERN_WARNING "%s: ientry=%p ientry->wd=%d ientry->group=%p "
                        "entry->inode=%p found_ientry=%p found_ientry->wd=%d "
                        "found_ientry->group=%p found_ientry->inode=%p\n",
                        __func__, ientry, ientry->wd, ientry->fsn_entry.group,
                        ientry->fsn_entry.inode, found_ientry, found_ientry->wd,
                        found_ientry->fsn_entry.group,
                        found_ientry->fsn_entry.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(&ientry->fsn_entry.refcnt) < 3)) {
                printk(KERN_WARNING "%s: ientry=%p ientry->wd=%d ientry->group=%p"
                        " ientry->inode=%p\n", __func__, ientry, ientry->wd,
                        ientry->fsn_entry.group, ientry->fsn_entry.inode);
                /* we can't really recover with bad ref cnting.. */
                BUG();
        }

        do_inotify_remove_from_idr(group, ientry);
out:
        /* match the ref taken by inotify_idr_find_locked() */
        if (found_ientry)
                fsnotify_put_mark(&found_ientry->fsn_entry);
        ientry->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_entry *entry,
                                    struct fsnotify_group *group)
{
        struct inotify_inode_mark_entry *ientry;
        struct fsnotify_event *ignored_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;

        ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry);

        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 = ientry->wd;

        ret = fsnotify_add_notify_event(group, ignored_event, fsn_event_priv, NULL);
        if (ret)
                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 entry from the idr */
        inotify_remove_from_idr(group, ientry);

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

/* ding dong the mark is dead */
static void inotify_free_mark(struct fsnotify_mark_entry *entry)
{
        struct inotify_inode_mark_entry *ientry;

        ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry);

        kmem_cache_free(inotify_inode_mark_cachep, ientry);
}

static int inotify_update_existing_watch(struct fsnotify_group *group,
                                         struct inode *inode,
                                         u32 arg)
{
        struct fsnotify_mark_entry *entry;
        struct inotify_inode_mark_entry *ientry;
        __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))
                return -EINVAL;

        spin_lock(&inode->i_lock);
        entry = fsnotify_find_mark_entry(group, inode);
        spin_unlock(&inode->i_lock);
        if (!entry)
                return -ENOENT;

        ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry);

        spin_lock(&entry->lock);

        old_mask = entry->mask;
        if (add) {
                entry->mask |= mask;
                new_mask = entry->mask;
        } else {
                entry->mask = mask;
                new_mask = entry->mask;
        }

        spin_unlock(&entry->lock);

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

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

                /* update the group mask with the new mask */
                if (dropped || do_group)
                        fsnotify_recalc_group_mask(group);
        }

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

        /* match the get from fsnotify_find_mark_entry() */
        fsnotify_put_mark(entry);

        return ret;
}

static int inotify_new_watch(struct fsnotify_group *group,
                             struct inode *inode,
                             u32 arg)
{
        struct inotify_inode_mark_entry *tmp_ientry;
        __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))
                return -EINVAL;

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

        fsnotify_init_mark(&tmp_ientry->fsn_entry, inotify_free_mark);
        tmp_ientry->fsn_entry.mask = mask;
        tmp_ientry->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_ientry);
        if (ret)
                goto out_err;

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

        /* update the idr hint, who cares about races, it's just a hint */
        group->inotify_data.last_wd = tmp_ientry->wd;

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

        /* return the watch descriptor for this new entry */
        ret = tmp_ientry->wd;

        /* if this mark added a new event update the group mask */
        if (mask & ~group->mask)
                fsnotify_recalc_group_mask(group);

out_err:
        /* match the ref from fsnotify_init_markentry() */
        fsnotify_put_mark(&tmp_ientry->fsn_entry);

        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(struct user_struct *user, unsigned int max_events)
{
        struct fsnotify_group *group;

        group = fsnotify_obtain_group(0, &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 = user;
        group->inotify_data.fa = NULL;

        return group;
}


/* inotify syscalls */
SYSCALL_DEFINE1(inotify_init1, int, flags)
{
        struct fsnotify_group *group;
        struct user_struct *user;
        struct file *filp;
        int fd, 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;

        fd = get_unused_fd_flags(flags & O_CLOEXEC);
        if (fd < 0)
                return fd;

        filp = get_empty_filp();
        if (!filp) {
                ret = -ENFILE;
                goto out_put_fd;
        }

        user = get_current_user();
        if (unlikely(atomic_read(&user->inotify_devs) >=
                        inotify_max_user_instances)) {
                ret = -EMFILE;
                goto out_free_uid;
        }

        /* fsnotify_obtain_group took a reference to group, we put this when we kill the file in the end */
        group = inotify_new_group(user, inotify_max_queued_events);
        if (IS_ERR(group)) {
                ret = PTR_ERR(group);
                goto out_free_uid;
        }

        filp->f_op = &inotify_fops;
        filp->f_path.mnt = mntget(inotify_mnt);
        filp->f_path.dentry = dget(inotify_mnt->mnt_root);
        filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping;
        filp->f_mode = FMODE_READ;
        filp->f_flags = O_RDONLY | (flags & O_NONBLOCK);
        filp->private_data = group;

        atomic_inc(&user->inotify_devs);

        fd_install(fd, filp);

        return fd;

out_free_uid:
        free_uid(user);
        put_filp(filp);
out_put_fd:
        put_unused_fd(fd);
        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 file *filp;
        int ret, fput_needed;
        unsigned flags = 0;

        filp = fget_light(fd, &fput_needed);
        if (unlikely(!filp))
                return -EBADF;

        /* verify that this is indeed an inotify instance */
        if (unlikely(filp->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 = filp->private_data;

        /* create/update an inode mark */
        ret = inotify_update_watch(group, inode, mask);
        if (unlikely(ret))
                goto path_put_and_out;

path_put_and_out:
        path_put(&path);
fput_and_out:
        fput_light(filp, fput_needed);
        return ret;
}

SYSCALL_DEFINE2(inotify_rm_watch, int, fd, __s32, wd)
{
        struct fsnotify_group *group;
        struct inotify_inode_mark_entry *ientry;
        struct file *filp;
        int ret = 0, fput_needed;

        filp = fget_light(fd, &fput_needed);
        if (unlikely(!filp))
                return -EBADF;

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

        group = filp->private_data;

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

        ret = 0;

        fsnotify_destroy_mark_by_entry(&ientry->fsn_entry);

        /* match ref taken by inotify_idr_find */
        fsnotify_put_mark(&ientry->fsn_entry);

out:
        fput_light(filp, fput_needed);
        return ret;
}

static int
inotify_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, "inotify", NULL,
                        INOTIFYFS_SUPER_MAGIC, mnt);
}

static struct file_system_type inotify_fs_type = {
    .name       = "inotifyfs",
    .get_sb     = inotify_get_sb,
    .kill_sb    = kill_anon_super,
};

/*
 * inotify_user_setup - Our initialization function.  Note that we cannnot 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)
{
        int ret;

        ret = register_filesystem(&inotify_fs_type);
        if (unlikely(ret))
                panic("inotify: register_filesystem returned %d!\n", ret);

        inotify_mnt = kern_mount(&inotify_fs_type);
        if (IS_ERR(inotify_mnt))
                panic("inotify: kern_mount ret %ld!\n", PTR_ERR(inotify_mnt));

        inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark_entry, 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);