fsnotify: allow marks to not pin inodes in core

inotify marks must pin inodes in core.  dnotify doesn't technically need to
since they are closed when the directory is closed.  fanotify also need to
pin inodes in core as it works today.  But the next step is to introduce
the concept of 'ignored masks' which is actually a mask of events for an
inode of no interest.  I claim that these should be liberally sent to the
kernel and should not pin the inode in core.  If the inode is brought back
in the listener will get an event it may have thought excluded, but this is
not a serious situation and one any listener should deal with.

This patch lays the ground work for non-pinning inode marks by using lazy
inode pinning.  We do not pin a mark until it has a non-zero mask entry.  If a
listener new sets a mask we never pin the inode.

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

1 files changed, 27 insertions, 8 deletions

diff --git a/fs/notify/inode_mark.c b/fs/notify/inode_mark.c
index c925579..4292f9e 100644
--- a/fs/notify/inode_mark.c
+++ b/fs/notify/inode_mark.c
@@ -141,7 +141,32 @@ struct fsnotify_mark *fsnotify_find_inode_mark(struct fsnotify_group *group,
 }
 
 /*
- * Attach an initialized mark mark to a given group and inode.
+ * If we are setting a mark mask on an inode mark we should pin the inode
+ * in memory.
+ */
+void fsnotify_set_inode_mark_mask_locked(struct fsnotify_mark *mark,
+					 __u32 mask)
+{
+	struct inode *inode;
+
+	assert_spin_locked(&mark->lock);
+
+	if (mask &&
+	    mark->i.inode &&
+	    !(mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED)) {
+		mark->flags |= FSNOTIFY_MARK_FLAG_OBJECT_PINNED;
+		inode = igrab(mark->i.inode);
+		/*
+		 * we shouldn't be able to get here if the inode wasn't
+		 * already safely held in memory.  But bug in case it
+		 * ever is wrong.
+		 */
+		BUG_ON(!inode);
+	}
+}
+
+/*
+ * Attach an initialized mark to a given group and inode.
  * These marks may be used for the fsnotify backend to determine which
  * event types should be delivered to which group and for which inodes.
  */
@@ -152,10 +177,6 @@ int fsnotify_add_inode_mark(struct fsnotify_mark *mark,
 	struct fsnotify_mark *lmark = NULL;
 	int ret = 0;
 
-	inode = igrab(inode);
-	if (unlikely(!inode))
-		return -EINVAL;
-
 	mark->flags = FSNOTIFY_MARK_FLAG_INODE;
 
 	assert_spin_locked(&mark->lock);
@@ -175,10 +196,8 @@ int fsnotify_add_inode_mark(struct fsnotify_mark *mark,
 
 	spin_unlock(&inode->i_lock);
 
-	if (lmark) {
+	if (lmark)
 		ret = -EEXIST;
-		iput(inode);
-	}
 
 	return ret;
 }