Pull bugzilla-5653 into release branch

[mirror_ubuntu-focal-kernel.git] / fs / inotify.c

/*
 * fs/inotify.c - inode-based file event notifications
 *
 * Authors:
 *      John McCutchan  <ttb@tentacle.dhs.org>
 *      Robert Love     <rml@novell.com>
 *
 * Copyright (C) 2005 John McCutchan
 *
 * 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/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/idr.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/writeback.h>
#include <linux/inotify.h>
#include <linux/syscalls.h>

#include <asm/ioctls.h>

static atomic_t inotify_cookie;

static kmem_cache_t *watch_cachep __read_mostly;
static kmem_cache_t *event_cachep __read_mostly;

static struct vfsmount *inotify_mnt __read_mostly;

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

/*
 * Lock ordering:
 *
 * dentry->d_lock (used to keep d_move() away from dentry->d_parent)
 * iprune_mutex (synchronize shrink_icache_memory())
 *      inode_lock (protects the super_block->s_inodes list)
 *      inode->inotify_mutex (protects inode->inotify_watches and watches->i_list)
 *              inotify_dev->mutex (protects inotify_device and watches->d_list)
 */

/*
 * Lifetimes of the three main data structures--inotify_device, inode, and
 * inotify_watch--are managed by reference count.
 *
 * inotify_device: Lifetime is from inotify_init() until release.  Additional
 * references can bump the count via get_inotify_dev() and drop the count via
 * put_inotify_dev().
 *
 * inotify_watch: Lifetime is from create_watch() to destory_watch().
 * Additional references can bump the count via get_inotify_watch() and drop
 * the count via put_inotify_watch().
 *
 * inode: Pinned so long as the inode is associated with a watch, from
 * create_watch() to put_inotify_watch().
 */

/*
 * struct inotify_device - represents an inotify instance
 *
 * This structure is protected by the mutex 'mutex'.
 */
struct inotify_device {
        wait_queue_head_t       wq;             /* wait queue for i/o */
        struct idr              idr;            /* idr mapping wd -> watch */
        struct mutex            mutex;          /* protects this bad boy */
        struct list_head        events;         /* list of queued events */
        struct list_head        watches;        /* list of watches */
        atomic_t                count;          /* reference count */
        struct user_struct      *user;          /* user who opened this dev */
        unsigned int            queue_size;     /* size of the queue (bytes) */
        unsigned int            event_count;    /* number of pending events */
        unsigned int            max_events;     /* maximum number of events */
        u32                     last_wd;        /* the last wd allocated */
};

/*
 * struct inotify_kernel_event - An inotify event, originating from a watch and
 * queued for user-space.  A list of these is attached to each instance of the
 * device.  In read(), this list is walked and all events that can fit in the
 * buffer are returned.
 *
 * Protected by dev->mutex of the device in which we are queued.
 */
struct inotify_kernel_event {
        struct inotify_event    event;  /* the user-space event */
        struct list_head        list;   /* entry in inotify_device's list */
        char                    *name;  /* filename, if any */
};

/*
 * struct inotify_watch - represents a watch request on a specific inode
 *
 * d_list is protected by dev->mutex of the associated watch->dev.
 * i_list and mask are protected by inode->inotify_mutex of the associated inode.
 * dev, inode, and wd are never written to once the watch is created.
 */
struct inotify_watch {
        struct list_head        d_list; /* entry in inotify_device's list */
        struct list_head        i_list; /* entry in inode's list */
        atomic_t                count;  /* reference count */
        struct inotify_device   *dev;   /* associated device */
        struct inode            *inode; /* associated inode */
        s32                     wd;     /* watch descriptor */
        u32                     mask;   /* event mask for this watch */
};

#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 void get_inotify_dev(struct inotify_device *dev)
{
        atomic_inc(&dev->count);
}

static inline void put_inotify_dev(struct inotify_device *dev)
{
        if (atomic_dec_and_test(&dev->count)) {
                atomic_dec(&dev->user->inotify_devs);
                free_uid(dev->user);
                idr_destroy(&dev->idr);
                kfree(dev);
        }
}

static inline void get_inotify_watch(struct inotify_watch *watch)
{
        atomic_inc(&watch->count);
}

/*
 * put_inotify_watch - decrements the ref count on a given watch.  cleans up
 * the watch and its references if the count reaches zero.
 */
static inline void put_inotify_watch(struct inotify_watch *watch)
{
        if (atomic_dec_and_test(&watch->count)) {
                put_inotify_dev(watch->dev);
                iput(watch->inode);
                kmem_cache_free(watch_cachep, watch);
        }
}

/*
 * kernel_event - create a new kernel event with the given parameters
 *
 * This function can sleep.
 */
static struct inotify_kernel_event * kernel_event(s32 wd, u32 mask, u32 cookie,
                                                  const char *name)
{
        struct inotify_kernel_event *kevent;

        kevent = kmem_cache_alloc(event_cachep, GFP_KERNEL);
        if (unlikely(!kevent))
                return NULL;

        /* we hand this out to user-space, so zero it just in case */
        memset(&kevent->event, 0, sizeof(struct inotify_event));

        kevent->event.wd = wd;
        kevent->event.mask = mask;
        kevent->event.cookie = cookie;

        INIT_LIST_HEAD(&kevent->list);

        if (name) {
                size_t len, rem, event_size = sizeof(struct inotify_event);

                /*
                 * We need to pad the filename so as to properly align an
                 * array of inotify_event structures.  Because the structure is
                 * small and the common case is a small filename, we just round
                 * up to the next multiple of the structure's sizeof.  This is
                 * simple and safe for all architectures.
                 */
                len = strlen(name) + 1;
                rem = event_size - len;
                if (len > event_size) {
                        rem = event_size - (len % event_size);
                        if (len % event_size == 0)
                                rem = 0;
                }

                kevent->name = kmalloc(len + rem, GFP_KERNEL);
                if (unlikely(!kevent->name)) {
                        kmem_cache_free(event_cachep, kevent);
                        return NULL;
                }
                memcpy(kevent->name, name, len);
                if (rem)
                        memset(kevent->name + len, 0, rem);             
                kevent->event.len = len + rem;
        } else {
                kevent->event.len = 0;
                kevent->name = NULL;
        }

        return kevent;
}

/*
 * inotify_dev_get_event - return the next event in the given dev's queue
 *
 * Caller must hold dev->mutex.
 */
static inline struct inotify_kernel_event *
inotify_dev_get_event(struct inotify_device *dev)
{
        return list_entry(dev->events.next, struct inotify_kernel_event, list);
}

/*
 * inotify_dev_queue_event - add a new event to the given device
 *
 * Caller must hold dev->mutex.  Can sleep (calls kernel_event()).
 */
static void inotify_dev_queue_event(struct inotify_device *dev,
                                    struct inotify_watch *watch, u32 mask,
                                    u32 cookie, const char *name)
{
        struct inotify_kernel_event *kevent, *last;

        /* coalescing: drop this event if it is a dupe of the previous */
        last = inotify_dev_get_event(dev);
        if (last && last->event.mask == mask && last->event.wd == watch->wd &&
                        last->event.cookie == cookie) {
                const char *lastname = last->name;

                if (!name && !lastname)
                        return;
                if (name && lastname && !strcmp(lastname, name))
                        return;
        }

        /* the queue overflowed and we already sent the Q_OVERFLOW event */
        if (unlikely(dev->event_count > dev->max_events))
                return;

        /* if the queue overflows, we need to notify user space */
        if (unlikely(dev->event_count == dev->max_events))
                kevent = kernel_event(-1, IN_Q_OVERFLOW, cookie, NULL);
        else
                kevent = kernel_event(watch->wd, mask, cookie, name);

        if (unlikely(!kevent))
                return;

        /* queue the event and wake up anyone waiting */
        dev->event_count++;
        dev->queue_size += sizeof(struct inotify_event) + kevent->event.len;
        list_add_tail(&kevent->list, &dev->events);
        wake_up_interruptible(&dev->wq);
}

/*
 * remove_kevent - cleans up and ultimately frees the given kevent
 *
 * Caller must hold dev->mutex.
 */
static void remove_kevent(struct inotify_device *dev,
                          struct inotify_kernel_event *kevent)
{
        list_del(&kevent->list);

        dev->event_count--;
        dev->queue_size -= sizeof(struct inotify_event) + kevent->event.len;

        kfree(kevent->name);
        kmem_cache_free(event_cachep, kevent);
}

/*
 * inotify_dev_event_dequeue - destroy an event on the given device
 *
 * Caller must hold dev->mutex.
 */
static void inotify_dev_event_dequeue(struct inotify_device *dev)
{
        if (!list_empty(&dev->events)) {
                struct inotify_kernel_event *kevent;
                kevent = inotify_dev_get_event(dev);
                remove_kevent(dev, kevent);
        }
}

/*
 * inotify_dev_get_wd - returns the next WD for use by the given dev
 *
 * Callers must hold dev->mutex.  This function can sleep.
 */
static int inotify_dev_get_wd(struct inotify_device *dev,
                              struct inotify_watch *watch)
{
        int ret;

        do {
                if (unlikely(!idr_pre_get(&dev->idr, GFP_KERNEL)))
                        return -ENOSPC;
                ret = idr_get_new_above(&dev->idr, watch, dev->last_wd+1, &watch->wd);
        } while (ret == -EAGAIN);

        return ret;
}

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

        error = __user_walk(dirname, flags, nd);
        if (error)
                return error;
        /* you can only watch an inode if you have read permissions on it */
        error = vfs_permission(nd, MAY_READ);
        if (error) 
                path_release(nd);
        return error;
}

/*
 * inotify_inode_watched - returns nonzero if there are watches on this inode
 * and zero otherwise.  We call this lockless, we do not care if we race.
 */
static inline int inotify_inode_watched(struct inode *inode)
{
        return !list_empty(&inode->inotify_watches);
}

/*
 * Get child dentry flag into synch with parent inode.
 * Flag should always be clear for negative dentrys.
 */
static void set_dentry_child_flags(struct inode *inode, int watched)
{
        struct dentry *alias;

        spin_lock(&dcache_lock);
        list_for_each_entry(alias, &inode->i_dentry, d_alias) {
                struct dentry *child;

                list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
                        if (!child->d_inode) {
                                WARN_ON(child->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);
                                continue;
                        }
                        spin_lock(&child->d_lock);
                        if (watched) {
                                WARN_ON(child->d_flags &
                                                DCACHE_INOTIFY_PARENT_WATCHED);
                                child->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
                        } else {
                                WARN_ON(!(child->d_flags &
                                        DCACHE_INOTIFY_PARENT_WATCHED));
                                child->d_flags&=~DCACHE_INOTIFY_PARENT_WATCHED;
                        }
                        spin_unlock(&child->d_lock);
                }
        }
        spin_unlock(&dcache_lock);
}

/*
 * create_watch - creates a watch on the given device.
 *
 * Callers must hold dev->mutex.  Calls inotify_dev_get_wd() so may sleep.
 * Both 'dev' and 'inode' (by way of nameidata) need to be pinned.
 */
static struct inotify_watch *create_watch(struct inotify_device *dev,
                                          u32 mask, struct inode *inode)
{
        struct inotify_watch *watch;
        int ret;

        if (atomic_read(&dev->user->inotify_watches) >=
                        inotify_max_user_watches)
                return ERR_PTR(-ENOSPC);

        watch = kmem_cache_alloc(watch_cachep, GFP_KERNEL);
        if (unlikely(!watch))
                return ERR_PTR(-ENOMEM);

        ret = inotify_dev_get_wd(dev, watch);
        if (unlikely(ret)) {
                kmem_cache_free(watch_cachep, watch);
                return ERR_PTR(ret);
        }

        dev->last_wd = watch->wd;
        watch->mask = mask;
        atomic_set(&watch->count, 0);
        INIT_LIST_HEAD(&watch->d_list);
        INIT_LIST_HEAD(&watch->i_list);

        /* save a reference to device and bump the count to make it official */
        get_inotify_dev(dev);
        watch->dev = dev;

        /*
         * Save a reference to the inode and bump the ref count to make it
         * official.  We hold a reference to nameidata, which makes this safe.
         */
        watch->inode = igrab(inode);

        /* bump our own count, corresponding to our entry in dev->watches */
        get_inotify_watch(watch);

        atomic_inc(&dev->user->inotify_watches);

        return watch;
}

/*
 * inotify_find_dev - find the watch associated with the given inode and dev
 *
 * Callers must hold inode->inotify_mutex.
 */
static struct inotify_watch *inode_find_dev(struct inode *inode,
                                            struct inotify_device *dev)
{
        struct inotify_watch *watch;

        list_for_each_entry(watch, &inode->inotify_watches, i_list) {
                if (watch->dev == dev)
                        return watch;
        }

        return NULL;
}

/*
 * remove_watch_no_event - remove_watch() without the IN_IGNORED event.
 */
static void remove_watch_no_event(struct inotify_watch *watch,
                                  struct inotify_device *dev)
{
        list_del(&watch->i_list);
        list_del(&watch->d_list);

        if (!inotify_inode_watched(watch->inode))
                set_dentry_child_flags(watch->inode, 0);

        atomic_dec(&dev->user->inotify_watches);
        idr_remove(&dev->idr, watch->wd);
        put_inotify_watch(watch);
}

/*
 * remove_watch - Remove a watch from both the device and the inode.  Sends
 * the IN_IGNORED event to the given device signifying that the inode is no
 * longer watched.
 *
 * Callers must hold both inode->inotify_mutex and dev->mutex.  We drop a
 * reference to the inode before returning.
 *
 * The inode is not iput() so as to remain atomic.  If the inode needs to be
 * iput(), the call returns one.  Otherwise, it returns zero.
 */
static void remove_watch(struct inotify_watch *watch,struct inotify_device *dev)
{
        inotify_dev_queue_event(dev, watch, IN_IGNORED, 0, NULL);
        remove_watch_no_event(watch, dev);
}

/* Kernel API */

/*
 * inotify_d_instantiate - instantiate dcache entry for inode
 */
void inotify_d_instantiate(struct dentry *entry, struct inode *inode)
{
        struct dentry *parent;

        if (!inode)
                return;

        WARN_ON(entry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);
        spin_lock(&entry->d_lock);
        parent = entry->d_parent;
        if (parent->d_inode && inotify_inode_watched(parent->d_inode))
                entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
        spin_unlock(&entry->d_lock);
}

/*
 * inotify_d_move - dcache entry has been moved
 */
void inotify_d_move(struct dentry *entry)
{
        struct dentry *parent;

        parent = entry->d_parent;
        if (inotify_inode_watched(parent->d_inode))
                entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
        else
                entry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;
}

/**
 * inotify_inode_queue_event - queue an event to all watches on this inode
 * @inode: inode event is originating from
 * @mask: event mask describing this event
 * @cookie: cookie for synchronization, or zero
 * @name: filename, if any
 */
void inotify_inode_queue_event(struct inode *inode, u32 mask, u32 cookie,
                               const char *name)
{
        struct inotify_watch *watch, *next;

        if (!inotify_inode_watched(inode))
                return;

        mutex_lock(&inode->inotify_mutex);
        list_for_each_entry_safe(watch, next, &inode->inotify_watches, i_list) {
                u32 watch_mask = watch->mask;
                if (watch_mask & mask) {
                        struct inotify_device *dev = watch->dev;
                        get_inotify_watch(watch);
                        mutex_lock(&dev->mutex);
                        inotify_dev_queue_event(dev, watch, mask, cookie, name);
                        if (watch_mask & IN_ONESHOT)
                                remove_watch_no_event(watch, dev);
                        mutex_unlock(&dev->mutex);
                        put_inotify_watch(watch);
                }
        }
        mutex_unlock(&inode->inotify_mutex);
}
EXPORT_SYMBOL_GPL(inotify_inode_queue_event);

/**
 * inotify_dentry_parent_queue_event - queue an event to a dentry's parent
 * @dentry: the dentry in question, we queue against this dentry's parent
 * @mask: event mask describing this event
 * @cookie: cookie for synchronization, or zero
 * @name: filename, if any
 */
void inotify_dentry_parent_queue_event(struct dentry *dentry, u32 mask,
                                       u32 cookie, const char *name)
{
        struct dentry *parent;
        struct inode *inode;

        if (!(dentry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED))
                return;

        spin_lock(&dentry->d_lock);
        parent = dentry->d_parent;
        inode = parent->d_inode;

        if (inotify_inode_watched(inode)) {
                dget(parent);
                spin_unlock(&dentry->d_lock);
                inotify_inode_queue_event(inode, mask, cookie, name);
                dput(parent);
        } else
                spin_unlock(&dentry->d_lock);
}
EXPORT_SYMBOL_GPL(inotify_dentry_parent_queue_event);

/**
 * inotify_get_cookie - return a unique cookie for use in synchronizing events.
 */
u32 inotify_get_cookie(void)
{
        return atomic_inc_return(&inotify_cookie);
}
EXPORT_SYMBOL_GPL(inotify_get_cookie);

/**
 * inotify_unmount_inodes - an sb is unmounting.  handle any watched inodes.
 * @list: list of inodes being unmounted (sb->s_inodes)
 *
 * Called with inode_lock held, protecting the unmounting super block's list
 * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay.
 * We temporarily drop inode_lock, however, and CAN block.
 */
void inotify_unmount_inodes(struct list_head *list)
{
        struct inode *inode, *next_i, *need_iput = NULL;

        list_for_each_entry_safe(inode, next_i, list, i_sb_list) {
                struct inotify_watch *watch, *next_w;
                struct inode *need_iput_tmp;
                struct list_head *watches;

                /*
                 * If i_count is zero, the inode cannot have any watches and
                 * doing an __iget/iput with MS_ACTIVE clear would actually
                 * evict all inodes with zero i_count from icache which is
                 * unnecessarily violent and may in fact be illegal to do.
                 */
                if (!atomic_read(&inode->i_count))
                        continue;

                /*
                 * We cannot __iget() an inode in state I_CLEAR, I_FREEING, or
                 * I_WILL_FREE which is fine because by that point the inode
                 * cannot have any associated watches.
                 */
                if (inode->i_state & (I_CLEAR | I_FREEING | I_WILL_FREE))
                        continue;

                need_iput_tmp = need_iput;
                need_iput = NULL;
                /* In case the remove_watch() drops a reference. */
                if (inode != need_iput_tmp)
                        __iget(inode);
                else
                        need_iput_tmp = NULL;
                /* In case the dropping of a reference would nuke next_i. */
                if ((&next_i->i_sb_list != list) &&
                                atomic_read(&next_i->i_count) &&
                                !(next_i->i_state & (I_CLEAR | I_FREEING |
                                        I_WILL_FREE))) {
                        __iget(next_i);
                        need_iput = next_i;
                }

                /*
                 * We can safely drop inode_lock here because we hold
                 * references on both inode and next_i.  Also no new inodes
                 * will be added since the umount has begun.  Finally,
                 * iprune_mutex keeps shrink_icache_memory() away.
                 */
                spin_unlock(&inode_lock);

                if (need_iput_tmp)
                        iput(need_iput_tmp);

                /* for each watch, send IN_UNMOUNT and then remove it */
                mutex_lock(&inode->inotify_mutex);
                watches = &inode->inotify_watches;
                list_for_each_entry_safe(watch, next_w, watches, i_list) {
                        struct inotify_device *dev = watch->dev;
                        mutex_lock(&dev->mutex);
                        inotify_dev_queue_event(dev, watch, IN_UNMOUNT,0,NULL);
                        remove_watch(watch, dev);
                        mutex_unlock(&dev->mutex);
                }
                mutex_unlock(&inode->inotify_mutex);
                iput(inode);            

                spin_lock(&inode_lock);
        }
}
EXPORT_SYMBOL_GPL(inotify_unmount_inodes);

/**
 * inotify_inode_is_dead - an inode has been deleted, cleanup any watches
 * @inode: inode that is about to be removed
 */
void inotify_inode_is_dead(struct inode *inode)
{
        struct inotify_watch *watch, *next;

        mutex_lock(&inode->inotify_mutex);
        list_for_each_entry_safe(watch, next, &inode->inotify_watches, i_list) {
                struct inotify_device *dev = watch->dev;
                mutex_lock(&dev->mutex);
                remove_watch(watch, dev);
                mutex_unlock(&dev->mutex);
        }
        mutex_unlock(&inode->inotify_mutex);
}
EXPORT_SYMBOL_GPL(inotify_inode_is_dead);

/* Device Interface */

static unsigned int inotify_poll(struct file *file, poll_table *wait)
{
        struct inotify_device *dev = file->private_data;
        int ret = 0;

        poll_wait(file, &dev->wq, wait);
        mutex_lock(&dev->mutex);
        if (!list_empty(&dev->events))
                ret = POLLIN | POLLRDNORM;
        mutex_unlock(&dev->mutex);

        return ret;
}

static ssize_t inotify_read(struct file *file, char __user *buf,
                            size_t count, loff_t *pos)
{
        size_t event_size = sizeof (struct inotify_event);
        struct inotify_device *dev;
        char __user *start;
        int ret;
        DEFINE_WAIT(wait);

        start = buf;
        dev = file->private_data;

        while (1) {
                int events;

                prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE);

                mutex_lock(&dev->mutex);
                events = !list_empty(&dev->events);
                mutex_unlock(&dev->mutex);
                if (events) {
                        ret = 0;
                        break;
                }

                if (file->f_flags & O_NONBLOCK) {
                        ret = -EAGAIN;
                        break;
                }

                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }

                schedule();
        }

        finish_wait(&dev->wq, &wait);
        if (ret)
                return ret;

        mutex_lock(&dev->mutex);
        while (1) {
                struct inotify_kernel_event *kevent;

                ret = buf - start;
                if (list_empty(&dev->events))
                        break;

                kevent = inotify_dev_get_event(dev);
                if (event_size + kevent->event.len > count)
                        break;

                if (copy_to_user(buf, &kevent->event, event_size)) {
                        ret = -EFAULT;
                        break;
                }
                buf += event_size;
                count -= event_size;

                if (kevent->name) {
                        if (copy_to_user(buf, kevent->name, kevent->event.len)){
                                ret = -EFAULT;
                                break;
                        }
                        buf += kevent->event.len;
                        count -= kevent->event.len;
                }

                remove_kevent(dev, kevent);
        }
        mutex_unlock(&dev->mutex);

        return ret;
}

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

        /*
         * Destroy all of the watches on this device.  Unfortunately, not very
         * pretty.  We cannot do a simple iteration over the list, because we
         * do not know the inode until we iterate to the watch.  But we need to
         * hold inode->inotify_mutex before dev->mutex.  The following works.
         */
        while (1) {
                struct inotify_watch *watch;
                struct list_head *watches;
                struct inode *inode;

                mutex_lock(&dev->mutex);
                watches = &dev->watches;
                if (list_empty(watches)) {
                        mutex_unlock(&dev->mutex);
                        break;
                }
                watch = list_entry(watches->next, struct inotify_watch, d_list);
                get_inotify_watch(watch);
                mutex_unlock(&dev->mutex);

                inode = watch->inode;
                mutex_lock(&inode->inotify_mutex);
                mutex_lock(&dev->mutex);

                /* make sure we didn't race with another list removal */
                if (likely(idr_find(&dev->idr, watch->wd)))
                        remove_watch_no_event(watch, dev);

                mutex_unlock(&dev->mutex);
                mutex_unlock(&inode->inotify_mutex);
                put_inotify_watch(watch);
        }

        /* destroy all of the events on this device */
        mutex_lock(&dev->mutex);
        while (!list_empty(&dev->events))
                inotify_dev_event_dequeue(dev);
        mutex_unlock(&dev->mutex);

        /* free this device: the put matching the get in inotify_init() */
        put_inotify_dev(dev);

        return 0;
}

/*
 * inotify_ignore - remove a given wd from this inotify instance.
 *
 * Can sleep.
 */
static int inotify_ignore(struct inotify_device *dev, s32 wd)
{
        struct inotify_watch *watch;
        struct inode *inode;

        mutex_lock(&dev->mutex);
        watch = idr_find(&dev->idr, wd);
        if (unlikely(!watch)) {
                mutex_unlock(&dev->mutex);
                return -EINVAL;
        }
        get_inotify_watch(watch);
        inode = watch->inode;
        mutex_unlock(&dev->mutex);

        mutex_lock(&inode->inotify_mutex);
        mutex_lock(&dev->mutex);

        /* make sure that we did not race */
        if (likely(idr_find(&dev->idr, wd) == watch))
                remove_watch(watch, dev);

        mutex_unlock(&dev->mutex);
        mutex_unlock(&inode->inotify_mutex);
        put_inotify_watch(watch);

        return 0;
}

static long inotify_ioctl(struct file *file, unsigned int cmd,
                          unsigned long arg)
{
        struct inotify_device *dev;
        void __user *p;
        int ret = -ENOTTY;

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

        switch (cmd) {
        case FIONREAD:
                ret = put_user(dev->queue_size, (int __user *) p);
                break;
        }

        return ret;
}

static const struct file_operations inotify_fops = {
        .poll           = inotify_poll,
        .read           = inotify_read,
        .release        = inotify_release,
        .unlocked_ioctl = inotify_ioctl,
        .compat_ioctl   = inotify_ioctl,
};

asmlinkage long sys_inotify_init(void)
{
        struct inotify_device *dev;
        struct user_struct *user;
        struct file *filp;      
        int fd, ret;

        fd = get_unused_fd();
        if (fd < 0)
                return fd;

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

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

        dev = kmalloc(sizeof(struct inotify_device), GFP_KERNEL);
        if (unlikely(!dev)) {
                ret = -ENOMEM;
                goto out_free_uid;
        }

        filp->f_op = &inotify_fops;
        filp->f_vfsmnt = mntget(inotify_mnt);
        filp->f_dentry = dget(inotify_mnt->mnt_root);
        filp->f_mapping = filp->f_dentry->d_inode->i_mapping;
        filp->f_mode = FMODE_READ;
        filp->f_flags = O_RDONLY;
        filp->private_data = dev;

        idr_init(&dev->idr);
        INIT_LIST_HEAD(&dev->events);
        INIT_LIST_HEAD(&dev->watches);
        init_waitqueue_head(&dev->wq);
        mutex_init(&dev->mutex);
        dev->event_count = 0;
        dev->queue_size = 0;
        dev->max_events = inotify_max_queued_events;
        dev->user = user;
        dev->last_wd = 0;
        atomic_set(&dev->count, 0);

        get_inotify_dev(dev);
        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;
}

asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
{
        struct inotify_watch *watch, *old;
        struct inode *inode;
        struct inotify_device *dev;
        struct nameidata nd;
        struct file *filp;
        int ret, fput_needed;
        int mask_add = 0;
        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 = find_inode(path, &nd, flags);
        if (unlikely(ret))
                goto fput_and_out;

        /* inode held in place by reference to nd; dev by fget on fd */
        inode = nd.dentry->d_inode;
        dev = filp->private_data;

        mutex_lock(&inode->inotify_mutex);
        mutex_lock(&dev->mutex);

        if (mask & IN_MASK_ADD)
                mask_add = 1;

        /* don't let user-space set invalid bits: we don't want flags set */
        mask &= IN_ALL_EVENTS | IN_ONESHOT;
        if (unlikely(!mask)) {
                ret = -EINVAL;
                goto out;
        }

        /*
         * Handle the case of re-adding a watch on an (inode,dev) pair that we
         * are already watching.  We just update the mask and return its wd.
         */
        old = inode_find_dev(inode, dev);
        if (unlikely(old)) {
                if (mask_add)
                        old->mask |= mask;
                else
                        old->mask = mask;
                ret = old->wd;
                goto out;
        }

        watch = create_watch(dev, mask, inode);
        if (unlikely(IS_ERR(watch))) {
                ret = PTR_ERR(watch);
                goto out;
        }

        if (!inotify_inode_watched(inode))
                set_dentry_child_flags(inode, 1);

        /* Add the watch to the device's and the inode's list */
        list_add(&watch->d_list, &dev->watches);
        list_add(&watch->i_list, &inode->inotify_watches);
        ret = watch->wd;
out:
        mutex_unlock(&dev->mutex);
        mutex_unlock(&inode->inotify_mutex);
        path_release(&nd);
fput_and_out:
        fput_light(filp, fput_needed);
        return ret;
}

asmlinkage long sys_inotify_rm_watch(int fd, u32 wd)
{
        struct file *filp;
        struct inotify_device *dev;
        int ret, fput_needed;

        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 out;
        }

        dev = filp->private_data;
        ret = inotify_ignore(dev, wd);

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

static struct super_block *
inotify_get_sb(struct file_system_type *fs_type, int flags,
               const char *dev_name, void *data)
{
    return get_sb_pseudo(fs_type, "inotify", NULL, 0xBAD1DEA);
}

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

/*
 * inotify_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_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_max_queued_events = 16384;
        inotify_max_user_instances = 128;
        inotify_max_user_watches = 8192;

        atomic_set(&inotify_cookie, 0);

        watch_cachep = kmem_cache_create("inotify_watch_cache",
                                         sizeof(struct inotify_watch),
                                         0, SLAB_PANIC, NULL, NULL);
        event_cachep = kmem_cache_create("inotify_event_cache",
                                         sizeof(struct inotify_kernel_event),
                                         0, SLAB_PANIC, NULL, NULL);

        return 0;
}

module_init(inotify_setup);