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>

2 files changed, 2 insertions, 0 deletions

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 */