217 lines
6.7 KiB
C
217 lines
6.7 KiB
C
/*
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* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* Basic idea behind the notification queue: An fsnotify group (like inotify)
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* sends the userspace notification about events asynchronously some time after
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* the event happened. When inotify gets an event it will need to add that
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* event to the group notify queue. Since a single event might need to be on
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* multiple group's notification queues we can't add the event directly to each
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* queue and instead add a small "event_holder" to each queue. This event_holder
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* has a pointer back to the original event. Since the majority of events are
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* going to end up on one, and only one, notification queue we embed one
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* event_holder into each event. This means we have a single allocation instead
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* of always needing two. If the embedded event_holder is already in use by
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* another group a new event_holder (from fsnotify_event_holder_cachep) will be
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* allocated and used.
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*/
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/list.h>
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#include <linux/module.h>
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#include <linux/mount.h>
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#include <linux/mutex.h>
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#include <linux/namei.h>
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#include <linux/path.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/atomic.h>
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#include <linux/fsnotify_backend.h>
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#include "fsnotify.h"
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static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
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/**
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* fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
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* Called from fsnotify_move, which is inlined into filesystem modules.
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*/
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u32 fsnotify_get_cookie(void)
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{
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return atomic_inc_return(&fsnotify_sync_cookie);
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}
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EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
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/* return true if the notify queue is empty, false otherwise */
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bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
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{
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assert_spin_locked(&group->notification_lock);
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return list_empty(&group->notification_list) ? true : false;
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}
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void fsnotify_destroy_event(struct fsnotify_group *group,
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struct fsnotify_event *event)
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{
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/* Overflow events are per-group and we don't want to free them */
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if (!event || event->mask == FS_Q_OVERFLOW)
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return;
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/*
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* If the event is still queued, we have a problem... Do an unreliable
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* lockless check first to avoid locking in the common case. The
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* locking may be necessary for permission events which got removed
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* from the list by a different CPU than the one freeing the event.
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*/
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if (!list_empty(&event->list)) {
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spin_lock(&group->notification_lock);
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WARN_ON(!list_empty(&event->list));
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spin_unlock(&group->notification_lock);
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}
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group->ops->free_event(event);
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}
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/*
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* Add an event to the group notification queue. The group can later pull this
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* event off the queue to deal with. The function returns 0 if the event was
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* added to the queue, 1 if the event was merged with some other queued event,
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* 2 if the event was not queued - either the queue of events has overflown
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* or the group is shutting down.
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*/
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int fsnotify_add_event(struct fsnotify_group *group,
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struct fsnotify_event *event,
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int (*merge)(struct list_head *,
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struct fsnotify_event *))
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{
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int ret = 0;
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struct list_head *list = &group->notification_list;
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pr_debug("%s: group=%p event=%p\n", __func__, group, event);
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spin_lock(&group->notification_lock);
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if (group->shutdown) {
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spin_unlock(&group->notification_lock);
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return 2;
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}
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if (event == group->overflow_event ||
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group->q_len >= group->max_events) {
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ret = 2;
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/* Queue overflow event only if it isn't already queued */
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if (!list_empty(&group->overflow_event->list)) {
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spin_unlock(&group->notification_lock);
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return ret;
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}
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event = group->overflow_event;
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goto queue;
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}
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if (!list_empty(list) && merge) {
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ret = merge(list, event);
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if (ret) {
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spin_unlock(&group->notification_lock);
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return ret;
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}
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}
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queue:
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group->q_len++;
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list_add_tail(&event->list, list);
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spin_unlock(&group->notification_lock);
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wake_up(&group->notification_waitq);
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kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
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return ret;
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}
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/*
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* Remove and return the first event from the notification list. It is the
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* responsibility of the caller to destroy the obtained event
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*/
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struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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assert_spin_locked(&group->notification_lock);
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pr_debug("%s: group=%p\n", __func__, group);
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event = list_first_entry(&group->notification_list,
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struct fsnotify_event, list);
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/*
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* We need to init list head for the case of overflow event so that
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* check in fsnotify_add_event() works
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*/
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list_del_init(&event->list);
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group->q_len--;
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return event;
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}
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/*
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* This will not remove the event, that must be done with
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* fsnotify_remove_first_event()
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*/
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struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
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{
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assert_spin_locked(&group->notification_lock);
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return list_first_entry(&group->notification_list,
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struct fsnotify_event, list);
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}
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/*
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* Called when a group is being torn down to clean up any outstanding
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* event notifications.
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*/
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void fsnotify_flush_notify(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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spin_lock(&group->notification_lock);
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while (!fsnotify_notify_queue_is_empty(group)) {
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event = fsnotify_remove_first_event(group);
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spin_unlock(&group->notification_lock);
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fsnotify_destroy_event(group, event);
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spin_lock(&group->notification_lock);
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}
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spin_unlock(&group->notification_lock);
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}
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/*
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* fsnotify_create_event - Allocate a new event which will be sent to each
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* group's handle_event function if the group was interested in this
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* particular event.
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*
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* @inode the inode which is supposed to receive the event (sometimes a
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* parent of the inode to which the event happened.
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* @mask what actually happened.
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* @data pointer to the object which was actually affected
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* @data_type flag indication if the data is a file, path, inode, nothing...
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* @name the filename, if available
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*/
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void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
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u32 mask)
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{
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INIT_LIST_HEAD(&event->list);
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event->inode = inode;
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event->mask = mask;
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}
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