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/*
* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; see the file COPYING. If not, write to
* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/srcu.h>
#include <linux/rculist.h>
#include <linux/wait.h>
#include <linux/fsnotify_backend.h>
#include "fsnotify.h"
#include <asm/atomic.h>
/* protects writes to fsnotify_groups and fsnotify_mask */
static DEFINE_MUTEX(fsnotify_grp_mutex);
/* protects reads while running the fsnotify_groups list */
struct srcu_struct fsnotify_grp_srcu;
/* all groups registered to receive filesystem notifications */
LIST_HEAD(fsnotify_groups);
/* bitwise OR of all events (FS_*) interesting to some group on this system */
__u32 fsnotify_mask;
/*
* When a new group registers or changes it's set of interesting events
* this function updates the fsnotify_mask to contain all interesting events
*/
void fsnotify_recalc_global_mask(void)
{
struct fsnotify_group *group;
__u32 mask = 0;
int idx;
idx = srcu_read_lock(&fsnotify_grp_srcu);
list_for_each_entry_rcu(group, &fsnotify_groups, group_list)
mask |= group->mask;
srcu_read_unlock(&fsnotify_grp_srcu, idx);
fsnotify_mask = mask;
}
/*
* Take a reference to a group so things found under the fsnotify_grp_mutex
* can't get freed under us
*/
static void fsnotify_get_group(struct fsnotify_group *group)
{
atomic_inc(&group->refcnt);
}
/*
* Final freeing of a group
*/
static void fsnotify_destroy_group(struct fsnotify_group *group)
{
if (group->ops->free_group_priv)
group->ops->free_group_priv(group);
kfree(group);
}
/*
* Remove this group from the global list of groups that will get events
* this can be done even if there are still references and things still using
* this group. This just stops the group from getting new events.
*/
static void __fsnotify_evict_group(struct fsnotify_group *group)
{
BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex));
if (group->on_group_list)
list_del_rcu(&group->group_list);
group->on_group_list = 0;
}
/*
* Called when a group is no longer interested in getting events. This can be
* used if a group is misbehaving or if for some reason a group should no longer
* get any filesystem events.
*/
void fsnotify_evict_group(struct fsnotify_group *group)
{
mutex_lock(&fsnotify_grp_mutex);
__fsnotify_evict_group(group);
mutex_unlock(&fsnotify_grp_mutex);
}
/*
* Drop a reference to a group. Free it if it's through.
*/
void fsnotify_put_group(struct fsnotify_group *group)
{
if (!atomic_dec_and_mutex_lock(&group->refcnt, &fsnotify_grp_mutex))
return;
/*
* OK, now we know that there's no other users *and* we hold mutex,
* so no new references will appear
*/
__fsnotify_evict_group(group);
/*
* now it's off the list, so the only thing we might care about is
* srcu access....
*/
mutex_unlock(&fsnotify_grp_mutex);
synchronize_srcu(&fsnotify_grp_srcu);
/* and now it is really dead. _Nothing_ could be seeing it */
fsnotify_recalc_global_mask();
fsnotify_destroy_group(group);
}
/*
* Simply run the fsnotify_groups list and find a group which matches
* the given parameters. If a group is found we take a reference to that
* group.
*/
static struct fsnotify_group *fsnotify_find_group(unsigned int group_num, __u32 mask,
const struct fsnotify_ops *ops)
{
struct fsnotify_group *group_iter;
struct fsnotify_group *group = NULL;
BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex));
list_for_each_entry_rcu(group_iter, &fsnotify_groups, group_list) {
if (group_iter->group_num == group_num) {
if ((group_iter->mask == mask) &&
(group_iter->ops == ops)) {
fsnotify_get_group(group_iter);
group = group_iter;
} else
group = ERR_PTR(-EEXIST);
}
}
return group;
}
/*
* Either finds an existing group which matches the group_num, mask, and ops or
* creates a new group and adds it to the global group list. In either case we
* take a reference for the group returned.
*/
struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u32 mask,
const struct fsnotify_ops *ops)
{
struct fsnotify_group *group, *tgroup;
/* very low use, simpler locking if we just always alloc */
group = kmalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
if (!group)
return ERR_PTR(-ENOMEM);
atomic_set(&group->refcnt, 1);
group->on_group_list = 0;
group->group_num = group_num;
group->mask = mask;
group->ops = ops;
mutex_lock(&fsnotify_grp_mutex);
tgroup = fsnotify_find_group(group_num, mask, ops);
if (tgroup) {
/* group already exists */
mutex_unlock(&fsnotify_grp_mutex);
/* destroy the new one we made */
fsnotify_put_group(group);
return tgroup;
}
/* group not found, add a new one */
list_add_rcu(&group->group_list, &fsnotify_groups);
group->on_group_list = 1;
mutex_unlock(&fsnotify_grp_mutex);
if (mask)
fsnotify_recalc_global_mask();
return group;
}
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