I am afraid it might be a unionfs copyup_permissions() bug.
It copies some attributes of the inode, but timestamps.
When a user chmod to the file on ro branch, unionfs will copyup the
file, and the timestamps will be updated illegally.
/dev/shm/u$ grep union /proc/mounts
unionfs /dev/shm/u unionfs
rw,dirs=/dev/shm/rw=rw:/dev/shm/ro=ro,debug=0,delete=whiteout,copyup=preserve 0 0
/dev/shm/u$ ls -l ../r?/f_dst f_dst
-rw-r--r-- 1 jro jro 2 Dec 20 14:15 ../ro/f_dst
-rw-r--r-- 1 jro jro 2 Dec 20 14:15 f_dst
It shows 'f_dst' exists on ro branch only.
/dev/shm/u$ stat f_dst
File: `f_dst'
Size: 2 Blocks: 2 IO Block: 4096 regular file
Device: 22h/34d Inode: 4 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ jro) Gid: ( 1000/ jro)
Access: 2005-12-20 14:15:40.000000000 +0900
Modify: 2005-12-20 14:15:40.000000000 +0900
Change: 2005-12-20 14:15:40.000000000 +0900
/dev/shm/u$ chmod a+w f_dst
/dev/shm/u$ stat f_dst
File: `f_dst'
Size: 2 Blocks: 2 IO Block: 4096 regular file
Device: 22h/34d Inode: 4 Links: 1
Access: (0666/-rw-rw-rw-) Uid: ( 1000/ jro) Gid: ( 1000/ jro)
Access: 2005-12-20 14:17:24.000000000 +0900
Modify: 2005-12-20 14:17:24.000000000 +0900
Change: 2005-12-20 14:17:24.000000000 +0900
It shows three timestamps are updated after chmod.
In this case, mtime must not be changed.
Here is a patch.
Junjiro Okajima
--- unionfs-20051130-1554.orig/copyup.c 2005-12-01 05:54:06.000000000 +0900
+++ unionfs-20051130-1554/copyup.c 2005-12-20 14:12:02.000000000 +0900
@@ -137,7 +137,11 @@ static int copyup_permissions(struct sup
print_entry_location();
- newattrs.ia_valid = ATTR_CTIME;
+ newattrs.ia_atime = old_hidden_dentry->d_inode->i_atime;
+ newattrs.ia_mtime = old_hidden_dentry->d_inode->i_mtime;
+ newattrs.ia_ctime = old_hidden_dentry->d_inode->i_ctime;
+ newattrs.ia_valid = ATTR_CTIME | ATTR_ATIME | ATTR_MTIME |
+ ATTR_ATIME_SET | ATTR_MTIME_SET;
if (IS_SET(sb, COPYUP_FS_MOUNTER)) {
/* f/s mounter */
newattrs.ia_mode = stopd(sb)->copyupmode;
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