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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
*/
/*
* 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 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);
void fsnotify_destroy_event(struct fsnotify_group *group,
struct fsnotify_event *event)
{
/* Overflow events are per-group and we don't want to free them */
if (!event || event == group->overflow_event)
return;
/*
* If the event is still queued, we have a problem... Do an unreliable
* lockless check first to avoid locking in the common case. The
* locking may be necessary for permission events which got removed
* from the list by a different CPU than the one freeing the event.
*/
if (!list_empty(&event->list)) {
spin_lock(&group->notification_lock);
WARN_ON(!list_empty(&event->list));
spin_unlock(&group->notification_lock);
}
group->ops->free_event(event);
}
/*
* Try to add an event to the notification queue.
* The group can later pull this event off the queue to deal with.
* The group can use the @merge hook to merge the event with a queued event.
* The group can use the @insert hook to insert the event into hash table.
* The function returns:
* 0 if the event was added to a queue
* 1 if the event was merged with some other queued event
* 2 if the event was not queued - either the queue of events has overflown
* or the group is shutting down.
*/
int fsnotify_insert_event(struct fsnotify_group *group,
struct fsnotify_event *event,
int (*merge)(struct fsnotify_group *,
struct fsnotify_event *),
void (*insert)(struct fsnotify_group *,
struct fsnotify_event *))
{
int ret = 0;
struct list_head *list = &group->notification_list;
pr_debug("%s: group=%p event=%p\n", __func__, group, event);
spin_lock(&group->notification_lock);
if (group->shutdown) {
spin_unlock(&group->notification_lock);
return 2;
}
if (event == group->overflow_event ||
group->q_len >= group->max_events) {
ret = 2;
/* Queue overflow event only if it isn't already queued */
if (!list_empty(&group->overflow_event->list)) {
spin_unlock(&group->notification_lock);
return ret;
}
event = group->overflow_event;
goto queue;
}
if (!list_empty(list) && merge) {
ret = merge(group, event);
if (ret) {
spin_unlock(&group->notification_lock);
return ret;
}
}
queue:
group->q_len++;
list_add_tail(&event->list, list);
if (insert)
insert(group, event);
spin_unlock(&group->notification_lock);
wake_up(&group->notification_waitq);
kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
return ret;
}
void fsnotify_remove_queued_event(struct fsnotify_group *group,
struct fsnotify_event *event)
{
assert_spin_locked(&group->notification_lock);
/*
* We need to init list head for the case of overflow event so that
* check in fsnotify_add_event() works
*/
list_del_init(&event->list);
group->q_len--;
}
/*
* Return the first event on the notification list without removing it.
* Returns NULL if the list is empty.
*/
struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
{
assert_spin_locked(&group->notification_lock);
if (fsnotify_notify_queue_is_empty(group))
return NULL;
return list_first_entry(&group->notification_list,
struct fsnotify_event, list);
}
/*
* Remove and return the first event from the notification list. It is the
* responsibility of the caller to destroy the obtained event
*/
struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
{
struct fsnotify_event *event = fsnotify_peek_first_event(group);
if (!event)
return NULL;
pr_debug("%s: group=%p event=%p\n", __func__, group, event);
fsnotify_remove_queued_event(group, 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;
spin_lock(&group->notification_lock);
while (!fsnotify_notify_queue_is_empty(group)) {
event = fsnotify_remove_first_event(group);
spin_unlock(&group->notification_lock);
fsnotify_destroy_event(group, event);
spin_lock(&group->notification_lock);
}
spin_unlock(&group->notification_lock);
}
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