linux-kernel - [PATCH -v3 6/8] fsnotify: add group priorities

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Message-ID: <20081125172123.17115.31274.stgit@paris.rdu.redhat.com>
Date:	Tue, 25 Nov 2008 12:21:23 -0500
From:	Eric Paris <eparis@...hat.com>
To:	linux-kernel@...r.kernel.org, malware-list@...ts.printk.net
Cc:	viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, arjan@...radead.org, hch@...radead.org,
	a.p.zijlstra@...llo.nl
Subject: [PATCH -v3 6/8] 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                |   28 ++++++++++++++++++++++++----
 include/linux/fsnotify_backend.h |    4 +++-
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/fs/notify/group.c b/fs/notify/group.c
index dcc0547..bb8d6c6 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -79,15 +79,17 @@ void fsnotify_put_group(struct fsnotify_group *group)
 	return;
 }
 
-struct fsnotify_group *fsnotify_find_group(unsigned int group_num, unsigned long mask, struct fsnotify_ops *ops)
+struct fsnotify_group *fsnotify_find_group(unsigned int priority, unsigned int group_num,
+					   unsigned long mask, struct fsnotify_ops *ops)
 {
 	struct fsnotify_group *group_iter;
 	struct fsnotify_group *group = NULL;
 
 	mutex_lock(&fsnotify_grp_mutex);
 	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;
@@ -105,6 +107,7 @@ struct fsnotify_group *fsnotify_find_group(unsigned int group_num, unsigned long
 
 	atomic_set(&group->refcnt, 1);
 
+	group->priority = priority;
 	group->group_num = group_num;
 	group->mask = mask;
 
@@ -114,9 +117,26 @@ struct fsnotify_group *fsnotify_find_group(unsigned int group_num, unsigned long
 
 	group->ops = ops;
 
-	/* add it */
-	list_add_rcu(&group->group_list, &fsnotify_groups);
+	/* Do we need to be the first entry? */
+	if (list_empty(&fsnotify_groups)) {
+		list_add_rcu(&group->group_list, &fsnotify_groups);
+		goto out;
+	}
+
+	list_for_each_entry(group_iter, &fsnotify_groups, group_list) {
+		/* 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);
+			break;
+		}
 
+		/* are we at the end?  if so insert at end */
+		if (list_is_last(&group_iter->group_list, &fsnotify_groups)) {
+			list_add_tail_rcu(&group->group_list, &fsnotify_groups);
+			break;
+		}
+	}
 out:
 	mutex_unlock(&fsnotify_grp_mutex);
 	fsnotify_recalc_global_mask();
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 6a7b95c..e0b5528 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -57,6 +57,8 @@ struct fsnotify_group {
 	struct mutex notification_mutex;/* protect the notification_list */
 	struct list_head notification_list;	/* list of event_holder this group needs to send to userspace */
 	wait_queue_head_t notification_waitq;	/* read() on the notification file blocks on this waitq */
+
+	unsigned int priority;		/* order this group should receive msgs.  low first */
 };
 
 #ifdef CONFIG_FSNOTIFY
@@ -67,7 +69,7 @@ extern void fsnotify(struct file *file, struct dentry *dentry, struct inode *ino
 /* called from fsnotify interfaces, such as fanotify or dnotify */
 extern void fsnotify_recalc_global_mask(void);
 extern void fsnotify_get_group(struct fsnotify_group *group);
-extern struct fsnotify_group *fsnotify_find_group(unsigned int group_num, unsigned long mask, struct fsnotify_ops *ops);
+extern struct fsnotify_group *fsnotify_find_group(unsigned int priority, unsigned int group_num, unsigned long mask, struct fsnotify_ops *ops);
 extern void fsnotify_put_group(struct fsnotify_group *group);
 #else
 

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