[RFC PATCH -v4 06/14] fsnotify: add group priorities

[Eric Paris <eparis@redhat.com>]

In preperation for blocking fsnotify calls group priorities must be added.
When multiple groups request the same event type the lowest priority group
will receive the notification first.

Signed-off-by: Eric Paris <eparis@redhat.com>
---

 fs/notify/group.c                |   30 ++++++++++++++++++++++++------
 include/linux/fsnotify_backend.h |    4 +++-
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/fs/notify/group.c b/fs/notify/group.c
index 40935c3..0dd6e82 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -49,7 +49,21 @@ void fsnotify_recalc_global_mask(void)
 
 static void fsnotify_add_group(struct fsnotify_group *group)
 {
-	list_add_rcu(&group->group_list, &fsnotify_groups);
+	int priority = group->priority;
+	struct fsnotify_group *group_iter;
+
+	list_for_each_entry(group_iter, &fsnotify_groups, group_list) {
+		BUG_ON(list_empty(&fsnotify_groups));
+		/* insert in front of this one? */
+		if (priority < group_iter->priority) {
+			/* I used list_add_tail() to insert in front of group_iter...  */
+			list_add_tail_rcu(&group->group_list, &group_iter->group_list);
+			return;
+		}
+	}
+
+	/* apparently we need to be the last entry */
+	list_add_tail_rcu(&group->group_list, &fsnotify_groups);
 }
 
 void fsnotify_get_group(struct fsnotify_group *group)
@@ -91,14 +105,16 @@ void fsnotify_put_group(struct fsnotify_group *group)
 	}
 }
 
-static struct fsnotify_group *fsnotify_find_group(unsigned int group_num, __u64 mask, const struct fsnotify_ops *ops)
+static struct fsnotify_group *fsnotify_find_group(unsigned int priority, unsigned int group_num,
+						  __u64 mask, const struct fsnotify_ops *ops)
 {
 	struct fsnotify_group *group_iter;
 	struct fsnotify_group *group = NULL;
 
 	list_for_each_entry_rcu(group_iter, &fsnotify_groups, group_list) {
-		if (group_iter->group_num == group_num) {
+		if (group_iter->priority == priority) {
 			if ((group_iter->mask == mask) &&
+			    (group_iter->group_num == group_num) &&
 			    (group_iter->ops == ops)) {
 				fsnotify_get_group(group_iter);
 				group = group_iter;
@@ -109,13 +125,14 @@ static struct fsnotify_group *fsnotify_find_group(unsigned int group_num, __u64
 	return group;
 }
 
-struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u64 mask, const struct fsnotify_ops *ops)
+struct fsnotify_group *fsnotify_obtain_group(unsigned int priority, unsigned int group_num,
+					     __u64 mask, const struct fsnotify_ops *ops)
 {
 	struct fsnotify_group *group, *tgroup;
 	int idx;
 
 	idx = srcu_read_lock(&fsnotify_grp_srcu_struct);
-	group = fsnotify_find_group(group_num, mask, ops);
+	group = fsnotify_find_group(priority, group_num, mask, ops);
 	srcu_read_unlock(&fsnotify_grp_srcu_struct, idx);
 	if (group)
 		return group;
@@ -126,6 +143,7 @@ struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u64 mask,
 
 	atomic_set(&group->refcnt, 1);
 
+	group->priority = priority;
 	group->group_num = group_num;
 	group->mask = mask;
 
@@ -133,7 +151,7 @@ struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u64 mask,
 	group->private = NULL;
 
 	mutex_lock(&fsnotify_grp_mutex);
-	tgroup = fsnotify_find_group(group_num, mask, ops);
+	tgroup = fsnotify_find_group(priority, group_num, mask, ops);
 	/* we raced and something else inserted the same group */
 	if (tgroup) {
 		mutex_unlock(&fsnotify_grp_mutex);
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 5264db1..924902e 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -85,6 +85,8 @@ struct fsnotify_group {
 
 	const struct fsnotify_ops *ops;	/* how this group handles things */
 
+	unsigned int priority;		/* order this group should receive msgs.  low first */
+
 	void *private;			/* private data for implementers (dnotify, inotify, fanotify) */
 };
 
@@ -95,7 +97,7 @@ extern void fsnotify(struct inode *to_tell, __u64 mask, void *data, int data_is)
 
 /* called from fsnotify interfaces, such as fanotify or dnotify */
 extern void fsnotify_recalc_global_mask(void);
-extern struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u64 mask, const struct fsnotify_ops *ops);
+extern struct fsnotify_group *fsnotify_obtain_group(unsigned int priority, unsigned int group_num, __u64 mask, const struct fsnotify_ops *ops);
 extern void fsnotify_put_group(struct fsnotify_group *group);
 extern void fsnotify_get_group(struct fsnotify_group *group);