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;
+}