diff options
Diffstat (limited to 'fs/notify/group.c')
| -rw-r--r-- | fs/notify/group.c | 198 |
1 files changed, 198 insertions, 0 deletions
diff --git a/fs/notify/group.c b/fs/notify/group.c new file mode 100644 index 000000000000..c6812953b968 --- /dev/null +++ b/fs/notify/group.c @@ -0,0 +1,198 @@ +/* + * 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; +} |