inotify: allow users to request not to recieve events on unlinked children

An inotify watch on a directory will send events for children even if those
children have been unlinked.  This patch add a new inotify flag IN_EXCL_UNLINK
which allows a watch to specificy they don't care about unlinked children.
This should fix performance problems seen by tasks which add a watch to
/tmp and then are overrun with events when other processes are reading and
writing to unlinked files they created in /tmp.

https://bugzilla.kernel.org/show_bug.cgi?id=16296

Requested-by: Matthias Clasen <mclasen@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

4 files changed, 12 insertions, 1 deletions

diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index 388a150c3d4a..9d332e7f5a5c 100644
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -22,6 +22,7 @@
  * General Public License for more details.
  */
 
+#include <linux/dcache.h> /* d_unlinked */
 #include <linux/fs.h> /* struct inode */
 #include <linux/fsnotify_backend.h>
 #include <linux/inotify.h>
@@ -157,6 +158,14 @@ static bool inotify_should_send_event(struct fsnotify_group *group, struct inode
         mask = (mask & ~FS_EVENT_ON_CHILD);
         send = (fsn_mark->mask & mask);
 
+        if (send && (fsn_mark->mask & FS_EXCL_UNLINK) &&
+            (data_type == FSNOTIFY_EVENT_PATH)) {
+                struct path *path  = data;
+
+                if (d_unlinked(path->dentry))
+                        send = false;
+        }
+
         /* find took a reference */
         fsnotify_put_mark(fsn_mark);
 
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index f381dafe8efb..dfc80f70e517 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -97,7 +97,7 @@ static inline __u32 inotify_arg_to_mask(u32 arg)
         mask = (FS_IN_IGNORED | FS_EVENT_ON_CHILD | FS_UNMOUNT);
 
         /* mask off the flags used to open the fd */
-        mask |= (arg & (IN_ALL_EVENTS | IN_ONESHOT));
+        mask |= (arg & (IN_ALL_EVENTS | IN_ONESHOT | IN_EXCL_UNLINK));
 
         return mask;
 }
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index b9b3f24ad4fc..4b809fcd4996 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -44,6 +44,7 @@
 #define FS_OPEN_PERM            0x00010000      /* open event in an permission hook */
 #define FS_ACCESS_PERM          0x00020000      /* access event in a permissions hook */
 
+#define FS_EXCL_UNLINK          0x04000000      /* do not send events if object is unlinked */
 #define FS_IN_ISDIR             0x40000000      /* event occurred against dir */
 #define FS_IN_ONESHOT           0x80000000      /* only send event once */
 
diff --git a/include/linux/inotify.h b/include/linux/inotify.h
index 94d209a1b689..b74f2ef2c368 100644
--- a/include/linux/inotify.h
+++ b/include/linux/inotify.h
@@ -51,6 +51,7 @@ struct inotify_event {
 /* special flags */
 #define IN_ONLYDIR              0x01000000      /* only watch the path if it is a directory */
 #define IN_DONT_FOLLOW          0x02000000      /* don't follow a sym link */
+#define IN_EXCL_UNLINK          0x04000000      /* exclude events on unlinked objects */
 #define IN_MASK_ADD             0x20000000      /* add to the mask of an already existing watch */
 #define IN_ISDIR                0x40000000      /* event occurred against dir */
 #define IN_ONESHOT              0x80000000      /* only send event once */