Line data    Source code

       1             : // SPDX-License-Identifier: GPL-2.0-or-later
       2             : /*
       3             :  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
       4             :  */
       5             : 
       6             : /*
       7             :  * Basic idea behind the notification queue: An fsnotify group (like inotify)
       8             :  * sends the userspace notification about events asynchronously some time after
       9             :  * the event happened.  When inotify gets an event it will need to add that
      10             :  * event to the group notify queue.  Since a single event might need to be on
      11             :  * multiple group's notification queues we can't add the event directly to each
      12             :  * queue and instead add a small "event_holder" to each queue.  This event_holder
      13             :  * has a pointer back to the original event.  Since the majority of events are
      14             :  * going to end up on one, and only one, notification queue we embed one
      15             :  * event_holder into each event.  This means we have a single allocation instead
      16             :  * of always needing two.  If the embedded event_holder is already in use by
      17             :  * another group a new event_holder (from fsnotify_event_holder_cachep) will be
      18             :  * allocated and used.
      19             :  */
      20             : 
      21             : #include <linux/fs.h>
      22             : #include <linux/init.h>
      23             : #include <linux/kernel.h>
      24             : #include <linux/list.h>
      25             : #include <linux/module.h>
      26             : #include <linux/mount.h>
      27             : #include <linux/mutex.h>
      28             : #include <linux/namei.h>
      29             : #include <linux/path.h>
      30             : #include <linux/slab.h>
      31             : #include <linux/spinlock.h>
      32             : 
      33             : #include <linux/atomic.h>
      34             : 
      35             : #include <linux/fsnotify_backend.h>
      36             : #include "fsnotify.h"
      37             : 
      38             : static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
      39             : 
      40             : /**
      41             :  * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
      42             :  * Called from fsnotify_move, which is inlined into filesystem modules.
      43             :  */
      44           0 : u32 fsnotify_get_cookie(void)
      45             : {
      46           0 :         return atomic_inc_return(&fsnotify_sync_cookie);
      47             : }
      48             : EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
      49             : 
      50           0 : void fsnotify_destroy_event(struct fsnotify_group *group,
      51             :                             struct fsnotify_event *event)
      52             : {
      53             :         /* Overflow events are per-group and we don't want to free them */
      54           0 :         if (!event || event == group->overflow_event)
      55             :                 return;
      56             :         /*
      57             :          * If the event is still queued, we have a problem... Do an unreliable
      58             :          * lockless check first to avoid locking in the common case. The
      59             :          * locking may be necessary for permission events which got removed
      60             :          * from the list by a different CPU than the one freeing the event.
      61             :          */
      62           0 :         if (!list_empty(&event->list)) {
      63           0 :                 spin_lock(&group->notification_lock);
      64           0 :                 WARN_ON(!list_empty(&event->list));
      65           0 :                 spin_unlock(&group->notification_lock);
      66             :         }
      67           0 :         group->ops->free_event(group, event);
      68             : }
      69             : 
      70             : /*
      71             :  * Try to add an event to the notification queue.
      72             :  * The group can later pull this event off the queue to deal with.
      73             :  * The group can use the @merge hook to merge the event with a queued event.
      74             :  * The group can use the @insert hook to insert the event into hash table.
      75             :  * The function returns:
      76             :  * 0 if the event was added to a queue
      77             :  * 1 if the event was merged with some other queued event
      78             :  * 2 if the event was not queued - either the queue of events has overflown
      79             :  *   or the group is shutting down.
      80             :  */
      81           0 : int fsnotify_insert_event(struct fsnotify_group *group,
      82             :                           struct fsnotify_event *event,
      83             :                           int (*merge)(struct fsnotify_group *,
      84             :                                        struct fsnotify_event *),
      85             :                           void (*insert)(struct fsnotify_group *,
      86             :                                          struct fsnotify_event *))
      87             : {
      88           0 :         int ret = 0;
      89           0 :         struct list_head *list = &group->notification_list;
      90             : 
      91             :         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
      92             : 
      93           0 :         spin_lock(&group->notification_lock);
      94             : 
      95           0 :         if (group->shutdown) {
      96           0 :                 spin_unlock(&group->notification_lock);
      97           0 :                 return 2;
      98             :         }
      99             : 
     100           0 :         if (event == group->overflow_event ||
     101           0 :             group->q_len >= group->max_events) {
     102           0 :                 ret = 2;
     103             :                 /* Queue overflow event only if it isn't already queued */
     104           0 :                 if (!list_empty(&group->overflow_event->list)) {
     105           0 :                         spin_unlock(&group->notification_lock);
     106           0 :                         return ret;
     107             :                 }
     108             :                 event = group->overflow_event;
     109             :                 goto queue;
     110             :         }
     111             : 
     112           0 :         if (!list_empty(list) && merge) {
     113           0 :                 ret = merge(group, event);
     114           0 :                 if (ret) {
     115           0 :                         spin_unlock(&group->notification_lock);
     116           0 :                         return ret;
     117             :                 }
     118             :         }
     119             : 
     120             : queue:
     121           0 :         group->q_len++;
     122           0 :         list_add_tail(&event->list, list);
     123           0 :         if (insert)
     124           0 :                 insert(group, event);
     125           0 :         spin_unlock(&group->notification_lock);
     126             : 
     127           0 :         wake_up(&group->notification_waitq);
     128           0 :         kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
     129           0 :         return ret;
     130             : }
     131             : 
     132           0 : void fsnotify_remove_queued_event(struct fsnotify_group *group,
     133             :                                   struct fsnotify_event *event)
     134             : {
     135             :         assert_spin_locked(&group->notification_lock);
     136             :         /*
     137             :          * We need to init list head for the case of overflow event so that
     138             :          * check in fsnotify_add_event() works
     139             :          */
     140           0 :         list_del_init(&event->list);
     141           0 :         group->q_len--;
     142           0 : }
     143             : 
     144             : /*
     145             :  * Return the first event on the notification list without removing it.
     146             :  * Returns NULL if the list is empty.
     147             :  */
     148           0 : struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
     149             : {
     150             :         assert_spin_locked(&group->notification_lock);
     151             : 
     152           0 :         if (fsnotify_notify_queue_is_empty(group))
     153             :                 return NULL;
     154             : 
     155           0 :         return list_first_entry(&group->notification_list,
     156             :                                 struct fsnotify_event, list);
     157             : }
     158             : 
     159             : /*
     160             :  * Remove and return the first event from the notification list.  It is the
     161             :  * responsibility of the caller to destroy the obtained event
     162             :  */
     163           0 : struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
     164             : {
     165           0 :         struct fsnotify_event *event = fsnotify_peek_first_event(group);
     166             : 
     167           0 :         if (!event)
     168             :                 return NULL;
     169             : 
     170           0 :         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
     171             : 
     172           0 :         fsnotify_remove_queued_event(group, event);
     173             : 
     174           0 :         return event;
     175             : }
     176             : 
     177             : /*
     178             :  * Called when a group is being torn down to clean up any outstanding
     179             :  * event notifications.
     180             :  */
     181           0 : void fsnotify_flush_notify(struct fsnotify_group *group)
     182             : {
     183             :         struct fsnotify_event *event;
     184             : 
     185           0 :         spin_lock(&group->notification_lock);
     186           0 :         while (!fsnotify_notify_queue_is_empty(group)) {
     187           0 :                 event = fsnotify_remove_first_event(group);
     188           0 :                 spin_unlock(&group->notification_lock);
     189           0 :                 fsnotify_destroy_event(group, event);
     190           0 :                 spin_lock(&group->notification_lock);
     191             :         }
     192           0 :         spin_unlock(&group->notification_lock);
     193           0 : }