/*
* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
*
* 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.
*
* You should have received a copy of the GNU General Public License
* along with this program; see the file COPYING. If not, write to
* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* Basic idea behind the notification queue: An fsnotify group (like inotify)
* sends the userspace notification about events asynchronously some time after
* the event happened. When inotify gets an event it will need to add that
* event to the group notify queue. Since a single event might need to be on
* multiple group's notification queues we can't add the event directly to each
* queue and instead add a small "event_holder" to each queue. This event_holder
* has a pointer back to the original event. Since the majority of events are
* going to end up on one, and only one, notification queue we embed one
* event_holder into each event. This means we have a single allocation instead
* of always needing two. If the embedded event_holder is already in use by
* another group a new event_holder (from fsnotify_event_holder_cachep) will be
* allocated and used.
*/
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/mutex.h>
#include <linux/namei.h>
#include <linux/path.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/atomic.h>
#include <linux/fsnotify_backend.h>
#include "fsnotify.h"
static struct kmem_cache *fsnotify_event_cachep;
static struct kmem_cache *fsnotify_event_holder_cachep;
/*
* This is a magic event we send when the q is too full. Since it doesn't
* hold real event information we just keep one system wide and use it any time
* it is needed. It's refcnt is set 1 at kernel init time and will never
* get set to 0 so it will never get 'freed'
*/
static struct fsnotify_event *q_overflow_event;
static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
/**
* fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
* Called from fsnotify_move, which is inlined into filesystem modules.
*/
u32 fsnotify_get_cookie(void)
{
return atomic_inc_return(&fsnotify_sync_cookie);
}
EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
/* return true if the notify queue is empty, false otherwise */
bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
{
BUG_ON(!mutex_is_locked(&group->notification_mutex));
return list_empty(&group->notification_list) ? true : false;
}
void fsnotify_get_event(struct fsnotify_event *event)
{
atomic_inc(&event->refcnt);
}
void fsnotify_put_event(struct fsnotify_event *event)
{
if (!event)
return;
if (atomic_dec_and_test(&event->refcnt)) {
pr_debug("%s: event=%p\n", __func__, event);
if (event->data_type == FSNOTIFY_EVENT_PATH)
path_put(&event->path);
BUG_ON(!list_empty(&event->private_data_list));
kfree(event->file_name);
put_pid(event->tgid);
kmem_cache_free(fsnotify_event_cachep, event);
}
}
struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
{
return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
}
void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
{
if (holder)
kmem_cache_free(fsnotify_event_holder_cachep, holder);
}
/*
* Find the private data that the group previously attached to this event when
* the group added the event to the notification queue (fsnotify_add_notify_event)
*/
struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
{
struct fsnotify_event_private_data *lpriv;
struct fsnotify_event_private_data *priv = NULL;
assert_spin_locked(&event->lock);
list_for_each_entry(lpriv, &event->private_data_list, event_list) {
if (lpriv->group == group) {
priv = lpriv;
list_del(&priv->event_list);
break;
}
}
return priv;
}
/*
* Add an event to the group notification queue. The group can later pull this
* event off the queue to deal with. If the event is successfully added to the
* group's notification queue, a reference is taken on event.
*/
struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
struct fsnotify_event_private_data *priv,
struct fsnotify_event *(*merge)(struct list_head *,
struct fsnotify_event *))
{
struct fsnotify_event *return_event = NULL;
struct fsnotify_event_holder *holder = NULL;
struct list_head *list = &group->notification_list;
pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv);
/*
* There is one fsnotify_event_holder embedded inside each fsnotify_event.
* Check if we expect to be able to use that holder. If not alloc a new
* holder.
* For the overflow event it's possible that something will use the in
* event holder before we get the lock so we may need to jump back and
* alloc a new holder, this can't happen for most events...
*/
if (!list_empty(&event->holder.event_list)) {
alloc_holder:
holder = fsnotify_alloc_event_holder();
if (!holder)
return ERR_PTR(-ENOMEM);
}
mutex_lock(&group->notification_mutex);
if (group->q_len >= group->max_events) {
event = q_overflow_event;
/*
* we need to return the overflow event
* which means we need a ref
*/
fsnotify_get_event(event);
return_event = event;
/* sorry, no private data on the overflow event */
priv = NULL;
}
if (!list_empty(list) && merge) {
struct fsnotify_event *tmp;
tmp = merge(list, event);
if (tmp) {
mutex_unlock(&group->notification_mutex);
if (return_event)
fsnotify_put_event(return_event);
if (holder != &event->holder)
fsnotify_destroy_event_holder(holder);
return tmp;
}
}
spin_lock(&event->lock);
if (list_empty(&event->holder.event_list)) {
if (unlikely(holder))
fsnotify_destroy_event_holder(holder);
holder = &event->holder;
} else if (unlikely(!holder)) {
/* between the time we checked above and got the lock the in
* event holder was used, go back and get a new one */
spin_unlock(&event->lock);
mutex_unlock(&group->notification_mutex);
if (return_event) {
fsnotify_put_event(return_event);
return_event = NULL;
}
goto alloc_holder;
}
group->q_len++;
holder->event = event;
fsnotify_get_event(event);
list_add_tail(&holder->event_list, list);
if (priv)
list_add_tail(&priv->event_list, &event->private_data_list);
spin_unlock(&event->lock);
mutex_unlock(&group->notification_mutex);
wake_up(&group->notification_waitq);
kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
return return_event;
}
/*
* Remove and return the first event from the notification list. There is a
* reference held on this event since it was on the list. It is the responsibility
* of the caller to drop this reference.
*/
struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
{
struct fsnotify_event *event;
struct fsnotify_event_holder *holder;
BUG_ON(!mutex_is_locked(&group->notification_mutex));
pr_debug("%s: group=%p\n", __func__, group);
holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
event = holder->event;
spin_lock(&event->lock);
holder->event = NULL;
list_del_init(&holder->event_list);
spin_unlock(&event->lock);
/* event == holder means we are referenced through the in event holder */
if (holder != &event->holder)
fsnotify_destroy_event_holder(holder);
group->q_len--;
return event;
}
/*
* This will not remove the event, that must be done with fsnotify_remove_notify_event()
*/
struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
{
struct fsnotify_event *event;
struct fsnotify_event_holder *holder;
BUG_ON(!mutex_is_locked(&group->notification_mutex));
holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
event = holder->event;
return event;
}
/*
* Called when a group is being torn down to clean up any outstanding
* event notifications.
*/
void fsnotify_flush_notify(struct fsnotify_group *group)
{
struct fsnotify_event *event;
struct fsnotify_event_private_data *priv;
mutex_lock(&group->notification_mutex);
while (!fsnotify_notify_queue_is_empty(group)) {
event = fsnotify_remove_notify_event(group);
/* if they don't implement free_event_priv they better not have attached any */
if (group->ops->free_event_priv) {
spin_lock(&event->lock);
priv = fsnotify_remove_priv_from_event(group, event);
spin_unlock(&event->lock);
if (priv)
group->ops->free_event_priv(priv);
}
fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
}
mutex_unlock(&group->notification_mutex);
}
static void initialize_event(struct fsnotify_event *event)
{
INIT_LIST_HEAD(&event->holder.event_list);
atomic_set(&event->refcnt, 1);
spin_lock_init(&event->lock);
INIT_LIST_HEAD(&event->private_data_list);
}
/*
* Caller damn well better be holding whatever mutex is protecting the
* old_holder->event_list and the new_event must be a clean event which
* cannot be found anywhere else in the kernel.
*/
int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,
struct fsnotify_event *new_event)
{
struct fsnotify_event *old_event = old_holder->event;
struct fsnotify_event_holder *new_holder = &new_event->holder;
enum event_spinlock_class {
SPINLOCK_OLD,
SPINLOCK_NEW,
};
pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, new_event);
/*
* if the new_event's embedded holder is in use someone
* screwed up and didn't give us a clean new event.
*/
BUG_ON(!list_empty(&new_holder->event_list));
spin_lock_nested(&old_event->lock, SPINLOCK_OLD);
spin_lock_nested(&new_event->lock, SPINLOCK_NEW);
new_holder->event = new_event;
list_replace_init(&old_holder->event_list, &new_holder->event_list);
spin_unlock(&new_event->lock);
spin_unlock(&old_event->lock);
/* event == holder means we are referenced through the in event holder */
if (old_holder != &old_event->holder)
fsnotify_destroy_event_holder(old_holder);
fsnotify_get_event(new_event); /* on the list take reference */
fsnotify_put_event(old_event); /* off the list, drop reference */
return 0;
}
struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event)
{
struct fsnotify_event *event;
event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
if (!event)
return NULL;
pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, event);
memcpy(event, old_event, sizeof(*event));
initialize_event(event);
if (event->name_len) {
event->file_name = kstrdup(old_event->file_name, GFP_KERNEL);
if (!event->file_name) {
kmem_cache_free(fsnotify_event_cachep, event);
return NULL;
}
}
event->tgid = get_pid(old_event->tgid);
if (event->data_type == FSNOTIFY_EVENT_PATH)
path_get(&event->path);
return event;
}
/*
* fsnotify_create_event - Allocate a new event which will be sent to each
* group's handle_event function if the group was interested in this
* particular event.
*
* @to_tell the inode which is supposed to receive the event (sometimes a
* parent of the inode to which the event happened.
* @mask what actually happened.
* @data pointer to the object which was actually affected
* @data_type flag indication if the data is a file, path, inode, nothing...
* @name the filename, if available
*/
struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
int data_type, const unsigned char *name,
u32 cookie, gfp_t gfp)
{
struct fsnotify_event *event;
event = kmem_cache_zalloc(fsnotify_event_cachep, gfp);
if (!event)
return NULL;
pr_debug("%s: event=%p to_tell=%p mask=%x data=%p data_type=%d\n",
__func__, event, to_tell, mask, data, data_type);
initialize_event(event);
if (name) {
event->file_name = kstrdup(name, gfp);
if (!event->file_name) {
kmem_cache_free(fsnotify_event_cachep, event);
return NULL;
}
event->name_len = strlen(event->file_name);
}
event->tgid = get_pid(task_tgid(current));
event->sync_cookie = cookie;
event->to_tell = to_tell;
event->data_type = data_type;
switch (data_type) {
case FSNOTIFY_EVENT_PATH: {
struct path *path = data;
event->path.dentry = path->dentry;
event->path.mnt = path->mnt;
path_get(&event->path);
break;
}
case FSNOTIFY_EVENT_INODE:
event->inode = data;
break;
case FSNOTIFY_EVENT_NONE:
event->inode = NULL;
event->path.dentry = NULL;
event->path.mnt = NULL;
break;
default:
BUG();
}
event->mask = mask;
return event;
}
static __init int fsnotify_notification_init(void)
{
fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
q_overflow_event = fsnotify_create_event(NULL, FS_Q_OVERFLOW, NULL,
FSNOTIFY_EVENT_NONE, NULL, 0,
GFP_KERNEL);
if (!q_overflow_event)
panic("unable to allocate fsnotify q_overflow_event\n");
return 0;
}
subsys_initcall(fsnotify_notification_init);
