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193 lines
5.7 KiB
193 lines
5.7 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* Copyright (C) 2008 Red Hat, Inc., Eric Paris <[email protected]> |
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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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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 == group->overflow_event) |
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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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* Try to add an event to the notification queue. |
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* The group can later pull this event off the queue to deal with. |
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* The group can use the @merge hook to merge the event with a queued event. |
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* The group can use the @insert hook to insert the event into hash table. |
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* The function returns: |
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* 0 if the event was added to a queue |
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* 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 fsnotify_group *, |
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struct fsnotify_event *), |
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void (*insert)(struct fsnotify_group *, |
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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(group, 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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if (insert) |
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insert(group, event); |
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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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void fsnotify_remove_queued_event(struct fsnotify_group *group, |
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struct fsnotify_event *event) |
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{ |
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assert_spin_locked(&group->notification_lock); |
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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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} |
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/* |
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* Return the first event on the notification list without removing it. |
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* Returns NULL if the list is empty. |
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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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if (fsnotify_notify_queue_is_empty(group)) |
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return NULL; |
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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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* 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 = fsnotify_peek_first_event(group); |
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if (!event) |
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return NULL; |
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pr_debug("%s: group=%p event=%p\n", __func__, group, event); |
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fsnotify_remove_queued_event(group, event); |
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return event; |
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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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