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

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Date:	Fri, 12 Dec 2008 16:51:46 -0500
From:	Eric Paris <eparis@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	a.p.zijlstra@...llo.nl, viro@...IV.linux.org.uk, hch@...radead.org,
	zbr@...emap.net, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk
Subject: [RFC PATCH -v4 06/14] fsnotify: add group priorities

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@...hat.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);
 

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