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 #include <linux/module.h>
  26
  27 #include <linux/fsnotify_backend.h>
  28 #include "fsnotify.h"
  29
  30 #include <linux/atomic.h>
  31
  32 /*
  33  * Final freeing of a group
  34  */
  35 static void fsnotify_final_destroy_group(struct fsnotify_group *group)
  36 {
  37         if (group->ops->free_group_priv)
  38                 group->ops->free_group_priv(group);
  39
  40         kfree(group);
  41 }
  42
  43 /*
  44  * Stop queueing new events for this group. Once this function returns
  45  * fsnotify_add_event() will not add any new events to the group's queue.
  46  */
  47 void fsnotify_group_stop_queueing(struct fsnotify_group *group)
  48 {
  49         spin_lock(&group->notification_lock);
  50         group->shutdown = true;
  51         spin_unlock(&group->notification_lock);
  52 }
  53
  54 /*
  55  * Trying to get rid of a group. Remove all marks, flush all events and release
  56  * the group reference.
  57  * Note that another thread calling fsnotify_clear_marks_by_group() may still
  58  * hold a ref to the group.
  59  */
  60 void fsnotify_destroy_group(struct fsnotify_group *group)
  61 {
  62         /*
  63          * Stop queueing new events. The code below is careful enough to not
  64          * require this but fanotify needs to stop queuing events even before
  65          * fsnotify_destroy_group() is called and this makes the other callers
  66          * of fsnotify_destroy_group() to see the same behavior.
  67          */
  68         fsnotify_group_stop_queueing(group);
  69
  70         /* Clear all marks for this group and queue them for destruction */
  71         fsnotify_clear_marks_by_group(group, FSNOTIFY_OBJ_ALL_TYPES);
  72
  73         /*
  74          * Some marks can still be pinned when waiting for response from
  75          * userspace. Wait for those now. fsnotify_prepare_user_wait() will
  76          * not succeed now so this wait is race-free.
  77          */
  78         wait_event(group->notification_waitq, !atomic_read(&group->user_waits));
  79
  80         /*
  81          * Wait until all marks get really destroyed. We could actually destroy
  82          * them ourselves instead of waiting for worker to do it, however that
  83          * would be racy as worker can already be processing some marks before
  84          * we even entered fsnotify_destroy_group().
  85          */
  86         fsnotify_wait_marks_destroyed();
  87
  88         /*
  89          * Since we have waited for fsnotify_mark_srcu in
  90          * fsnotify_mark_destroy_list() there can be no outstanding event
  91          * notification against this group. So clearing the notification queue
  92          * of all events is reliable now.
  93          */
  94         fsnotify_flush_notify(group);
  95
  96         /*
  97          * Destroy overflow event (we cannot use fsnotify_destroy_event() as
  98          * that deliberately ignores overflow events.
  99          */
 100         if (group->overflow_event)
 101                 group->ops->free_event(group->overflow_event);
 102
 103         fsnotify_put_group(group);
 104 }
 105
 106 /*
 107  * Get reference to a group.
 108  */
 109 void fsnotify_get_group(struct fsnotify_group *group)
 110 {
 111         refcount_inc(&group->refcnt);
 112 }
 113 EXPORT_SYMBOL_GPL(fsnotify_get_group);
 114
 115 /*
 116  * Drop a reference to a group.  Free it if it's through.
 117  */
 118 void fsnotify_put_group(struct fsnotify_group *group)
 119 {
 120         if (refcount_dec_and_test(&group->refcnt))
 121                 fsnotify_final_destroy_group(group);
 122 }
 123 EXPORT_SYMBOL_GPL(fsnotify_put_group);
 124
 125 /*
 126  * Create a new fsnotify_group and hold a reference for the group returned.
 127  */
 128 struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
 129 {
 130         struct fsnotify_group *group;
 131
 132         group = kzalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
 133         if (!group)
 134                 return ERR_PTR(-ENOMEM);
 135
 136         /* set to 0 when there a no external references to this group */
 137         refcount_set(&group->refcnt, 1);
 138         atomic_set(&group->num_marks, 0);
 139         atomic_set(&group->user_waits, 0);
 140
 141         spin_lock_init(&group->notification_lock);
 142         INIT_LIST_HEAD(&group->notification_list);
 143         init_waitqueue_head(&group->notification_waitq);
 144         group->max_events = UINT_MAX;
 145
 146         mutex_init(&group->mark_mutex);
 147         INIT_LIST_HEAD(&group->marks_list);
 148
 149         group->ops = ops;
 150
 151         return group;
 152 }
 153 EXPORT_SYMBOL_GPL(fsnotify_alloc_group);
 154
 155 int fsnotify_fasync(int fd, struct file *file, int on)
 156 {
 157         struct fsnotify_group *group = file->private_data;
 158
 159         return fasync_helper(fd, file, on, &group->fsn_fa) >= 0 ? 0 : -EIO;
 160 }