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