I got a question in the android emulator which use Yaffs2 file system:

When I create or delete a file in a directory, the mtime and ctime of
the directoy do not change. This issue does not appear in other
filesystems.

# cd /data
#
# mkdir test
# /data/busybox stat test
  File: "test"
  Size: 2048      	Blocks: 4          IO Block: 4096   directory
Device: 1f01h/7937d	Inode: 551         Links: 1
Access: (0777/drwxrwxrwx)  Uid: (    0/ UNKNOWN)   Gid: (    0/ UNKNOWN)
Access: 2009-05-21 03:22:21.000000000
Modify: 2009-05-21 03:22:21.000000000
Change: 2009-05-21 03:22:21.000000000

# cd test
# /data/busybox touch aaa
# /data/busybox stat aaa
  File: "aaa"
  Size: 0         	Blocks: 0          IO Block: 4096   regular empty file
Device: 1f01h/7937d	Inode: 561         Links: 1
Access: (0666/-rw-rw-rw-)  Uid: (    0/ UNKNOWN)   Gid: (    0/ UNKNOWN)
Access: 2009-05-21 03:23:15.000000000
Modify: 2009-05-21 03:23:15.000000000
Change: 2009-05-21 03:23:15.000000000

# cd ..
# /data/busybox stat test
  File: "test"
  Size: 2048      	Blocks: 4          IO Block: 4096   directory
Device: 1f01h/7937d	Inode: 551         Links: 1
Access: (0777/drwxrwxrwx)  Uid: (    0/ UNKNOWN)   Gid: (    0/ UNKNOWN)
Access: 2009-05-21 03:22:21.000000000
Modify: 2009-05-21 03:22:21.000000000
Change: 2009-05-21 03:22:21.000000000