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         396 : u32 fsnotify_get_cookie(void)
      45             : {
      46         396 :         return atomic_inc_return(&fsnotify_sync_cookie);
      47             : }
      48             : EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
      49             : 
      50             : /* return true if the notify queue is empty, false otherwise */
      51         540 : bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
      52             : {
      53         540 :         assert_spin_locked(&group->notification_lock);
      54         540 :         return list_empty(&group->notification_list) ? true : false;
      55             : }
      56             : 
      57         144 : void fsnotify_destroy_event(struct fsnotify_group *group,
      58             :                             struct fsnotify_event *event)
      59             : {
      60             :         /* Overflow events are per-group and we don't want to free them */
      61         144 :         if (!event || event == group->overflow_event)
      62             :                 return;
      63             :         /*
      64             :          * If the event is still queued, we have a problem... Do an unreliable
      65             :          * lockless check first to avoid locking in the common case. The
      66             :          * locking may be necessary for permission events which got removed
      67             :          * from the list by a different CPU than the one freeing the event.
      68             :          */
      69         144 :         if (!list_empty(&event->list)) {
      70           0 :                 spin_lock(&group->notification_lock);
      71           0 :                 WARN_ON(!list_empty(&event->list));
      72           0 :                 spin_unlock(&group->notification_lock);
      73             :         }
      74         144 :         group->ops->free_event(event);
      75             : }
      76             : 
      77             : /*
      78             :  * Add an event to the group notification queue.  The group can later pull this
      79             :  * event off the queue to deal with.  The function returns 0 if the event was
      80             :  * added to the queue, 1 if the event was merged with some other queued event,
      81             :  * 2 if the event was not queued - either the queue of events has overflown
      82             :  * or the group is shutting down.
      83             :  */
      84         144 : int fsnotify_add_event(struct fsnotify_group *group,
      85             :                        struct fsnotify_event *event,
      86             :                        int (*merge)(struct list_head *,
      87             :                                     struct fsnotify_event *))
      88             : {
      89         144 :         int ret = 0;
      90         144 :         struct list_head *list = &group->notification_list;
      91             : 
      92         144 :         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
      93             : 
      94         144 :         spin_lock(&group->notification_lock);
      95             : 
      96         144 :         if (group->shutdown) {
      97           6 :                 spin_unlock(&group->notification_lock);
      98           6 :                 return 2;
      99             :         }
     100             : 
     101         138 :         if (event == group->overflow_event ||
     102         138 :             group->q_len >= group->max_events) {
     103           0 :                 ret = 2;
     104             :                 /* Queue overflow event only if it isn't already queued */
     105           0 :                 if (!list_empty(&group->overflow_event->list)) {
     106           0 :                         spin_unlock(&group->notification_lock);
     107           0 :                         return ret;
     108             :                 }
     109           0 :                 event = group->overflow_event;
     110           0 :                 goto queue;
     111             :         }
     112             : 
     113         138 :         if (!list_empty(list) && merge) {
     114          74 :                 ret = merge(list, event);
     115          74 :                 if (ret) {
     116           5 :                         spin_unlock(&group->notification_lock);
     117           5 :                         return ret;
     118             :                 }
     119             :         }
     120             : 
     121         133 : queue:
     122         133 :         group->q_len++;
     123         133 :         list_add_tail(&event->list, list);
     124         133 :         spin_unlock(&group->notification_lock);
     125             : 
     126         133 :         wake_up(&group->notification_waitq);
     127         133 :         kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
     128         133 :         return ret;
     129             : }
     130             : 
     131         133 : void fsnotify_remove_queued_event(struct fsnotify_group *group,
     132             :                                   struct fsnotify_event *event)
     133             : {
     134         133 :         assert_spin_locked(&group->notification_lock);
     135             :         /*
     136             :          * We need to init list head for the case of overflow event so that
     137             :          * check in fsnotify_add_event() works
     138             :          */
     139         133 :         list_del_init(&event->list);
     140         133 :         group->q_len--;
     141         133 : }
     142             : 
     143             : /*
     144             :  * Remove and return the first event from the notification list.  It is the
     145             :  * responsibility of the caller to destroy the obtained event
     146             :  */
     147         133 : struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
     148             : {
     149         133 :         struct fsnotify_event *event;
     150             : 
     151         133 :         assert_spin_locked(&group->notification_lock);
     152             : 
     153         133 :         pr_debug("%s: group=%p\n", __func__, group);
     154             : 
     155         133 :         event = list_first_entry(&group->notification_list,
     156             :                                  struct fsnotify_event, list);
     157         133 :         fsnotify_remove_queued_event(group, event);
     158         133 :         return event;
     159             : }
     160             : 
     161             : /*
     162             :  * This will not remove the event, that must be done with
     163             :  * fsnotify_remove_first_event()
     164             :  */
     165         129 : struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
     166             : {
     167         129 :         assert_spin_locked(&group->notification_lock);
     168             : 
     169         129 :         return list_first_entry(&group->notification_list,
     170             :                                 struct fsnotify_event, list);
     171             : }
     172             : 
     173             : /*
     174             :  * Called when a group is being torn down to clean up any outstanding
     175             :  * event notifications.
     176             :  */
     177           7 : void fsnotify_flush_notify(struct fsnotify_group *group)
     178             : {
     179           7 :         struct fsnotify_event *event;
     180             : 
     181           7 :         spin_lock(&group->notification_lock);
     182          11 :         while (!fsnotify_notify_queue_is_empty(group)) {
     183           4 :                 event = fsnotify_remove_first_event(group);
     184           4 :                 spin_unlock(&group->notification_lock);
     185           4 :                 fsnotify_destroy_event(group, event);
     186          15 :                 spin_lock(&group->notification_lock);
     187             :         }
     188           7 :         spin_unlock(&group->notification_lock);
     189           7 : }