[PATCH] inotify: fix event loss on hardlinked files

People have run into a problem when they do this:

watch (file1, all_events);
watch (file2, some_events);

if file2 is a hard link to file1, some events will be missed because by
default we replace the mask.  The patch below adds a flag IN_MASK_ADD which
will cause inotify to add to the existing mask if present.

Signed-off-by: John McCutchan <ttb@tentacle.dhs.org>
Signed-off-by: Robert Love <rml@novell.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/inotify.c b/fs/inotify.c
index 2fd97ef547ffcac2b35a3bcee5a37667b8e51ef4..a37e9fb1da589fa1457929e2079e176220ad34c0 100644 (file)
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -931,6 +931,7 @@ asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
        struct nameidata nd;
        struct file *filp;
        int ret, fput_needed;
+       int mask_add = 0;
 
        filp = fget_light(fd, &fput_needed);
        if (unlikely(!filp))
@@ -953,6 +954,9 @@ asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
        down(&inode->inotify_sem);
        down(&dev->sem);
 
+       if (mask & IN_MASK_ADD)
+               mask_add = 1;
+
        /* don't let user-space set invalid bits: we don't want flags set */
        mask &= IN_ALL_EVENTS;
        if (unlikely(!mask)) {
@@ -966,7 +970,10 @@ asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
         */
        old = inode_find_dev(inode, dev);
        if (unlikely(old)) {
-               old->mask = mask;
+               if (mask_add)
+                       old->mask |= mask;
+               else
+                       old->mask = mask;
                ret = old->wd;
                goto out;
        }

diff --git a/include/linux/inotify.h b/include/linux/inotify.h
index 93bb3afe646bc315d1ce17849acdad149e9b8684..ee5b239092edbb03dee1765dd7919246bf4a2400 100644 (file)
--- a/include/linux/inotify.h
+++ b/include/linux/inotify.h
@@ -47,6 +47,7 @@ struct inotify_event {
 #define IN_MOVE                        (IN_MOVED_FROM | IN_MOVED_TO) /* moves */
 
 /* special flags */
+#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 */