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-rw-r--r--fs/notify/group.c198
1 files changed, 198 insertions, 0 deletions
diff --git a/fs/notify/group.c b/fs/notify/group.c
new file mode 100644
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--- /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;
+}