fs/notify/group.c

   1 /*
   2  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
   3  *
   4  *  This program is free software; you can redistribute it and/or modify
   5  *  it under the terms of the GNU General Public License as published by
   6  *  the Free Software Foundation; either version 2, or (at your option)
   7  *  any later version.
   8  *
   9  *  This program is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  *  GNU General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU General Public License
  15  *  along with this program; see the file COPYING.  If not, write to
  16  *  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 #include <linux/list.h>
  20 #include <linux/mutex.h>
  21 #include <linux/slab.h>
  22 #include <linux/srcu.h>
  23 #include <linux/rculist.h>
  24 #include <linux/wait.h>
  25
  26 #include <linux/fsnotify_backend.h>
  27 #include "fsnotify.h"
  28
  29 #include <linux/atomic.h>
  30
  31 /*
  32  * Final freeing of a group
  33  */
  34 static void fsnotify_final_destroy_group(struct fsnotify_group *group)
  35 {
  36         if (group->ops->free_group_priv)
  37                 group->ops->free_group_priv(group);
  38
  39         kfree(group);
  40 }
  41
  42 /*
  43  * Stop queueing new events for this group. Once this function returns
  44  * fsnotify_add_event() will not add any new events to the group's queue.
  45  */
  46 void fsnotify_group_stop_queueing(struct fsnotify_group *group)
  47 {
  48         spin_lock(&group->notification_lock);
  49         group->shutdown = true;
  50         spin_unlock(&group->notification_lock);
  51 }
  52
  53 /*
  54  * Trying to get rid of a group. Remove all marks, flush all events and release
  55  * the group reference.
  56  * Note that another thread calling fsnotify_clear_marks_by_group() may still
  57  * hold a ref to the group.
  58  */
  59 void fsnotify_destroy_group(struct fsnotify_group *group)
  60 {
  61         /*
  62          * Stop queueing new events. The code below is careful enough to not
  63          * require this but fanotify needs to stop queuing events even before
  64          * fsnotify_destroy_group() is called and this makes the other callers
  65          * of fsnotify_destroy_group() to see the same behavior.
  66          */
  67         fsnotify_group_stop_queueing(group);
  68
  69         /* Clear all marks for this group and queue them for destruction */
  70         fsnotify_clear_marks_by_group(group, FSNOTIFY_OBJ_ALL_TYPES);
  71
  72         /*
  73          * Some marks can still be pinned when waiting for response from
  74          * userspace. Wait for those now. fsnotify_prepare_user_wait() will
  75          * not succeed now so this wait is race-free.
  76          */
  77         wait_event(group->notification_waitq, !atomic_read(&group->user_waits));
  78
  79         /*
  80          * Wait until all marks get really destroyed. We could actually destroy
  81          * them ourselves instead of waiting for worker to do it, however that
  82          * would be racy as worker can already be processing some marks before
  83          * we even entered fsnotify_destroy_group().
  84          */
  85         fsnotify_wait_marks_destroyed();
  86
  87         /*
  88          * Since we have waited for fsnotify_mark_srcu in
  89          * fsnotify_mark_destroy_list() there can be no outstanding event
  90          * notification against this group. So clearing the notification queue
  91          * of all events is reliable now.
  92          */
  93         fsnotify_flush_notify(group);
  94
  95         /*
  96          * Destroy overflow event (we cannot use fsnotify_destroy_event() as
  97          * that deliberately ignores overflow events.
  98          */
  99         if (group->overflow_event)
 100                 group->ops->free_event(group->overflow_event);
 101
 102         fsnotify_put_group(group);
 103 }
 104
 105 /*
 106  * Get reference to a group.
 107  */
 108 void fsnotify_get_group(struct fsnotify_group *group)
 109 {
 110         atomic_inc(&group->refcnt);
 111 }
 112
 113 /*
 114  * Drop a reference to a group.  Free it if it's through.
 115  */
 116 void fsnotify_put_group(struct fsnotify_group *group)
 117 {
 118         if (atomic_dec_and_test(&group->refcnt))
 119                 fsnotify_final_destroy_group(group);
 120 }
 121
 122 /*
 123  * Create a new fsnotify_group and hold a reference for the group returned.
 124  */
 125 struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
 126 {
 127         struct fsnotify_group *group;
 128
 129         group = kzalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
 130         if (!group)
 131                 return ERR_PTR(-ENOMEM);
 132
 133         /* set to 0 when there a no external references to this group */
 134         atomic_set(&group->refcnt, 1);
 135         atomic_set(&group->num_marks, 0);
 136         atomic_set(&group->user_waits, 0);
 137
 138         spin_lock_init(&group->notification_lock);
 139         INIT_LIST_HEAD(&group->notification_list);
 140         init_waitqueue_head(&group->notification_waitq);
 141         group->max_events = UINT_MAX;
 142
 143         mutex_init(&group->mark_mutex);
 144         INIT_LIST_HEAD(&group->marks_list);
 145
 146         group->ops = ops;
 147
 148         return group;
 149 }
 150
 151 int fsnotify_fasync(int fd, struct file *file, int on)
 152 {
 153         struct fsnotify_group *group = file->private_data;
 154
 155         return fasync_helper(fd, file, on, &group->fsn_fa) >= 0 ? 0 : -EIO;
 156 }