Hi, theres' that irritating problem that two files on the same device and with same pathname -- but different content -- can have same inode number on NILFS2. It really can screw automated and manual backup/restore. Best of all, it seems to be against POSIX. Actually, two `versions' of the same file. Today I wanted to revert a config file to certain older version: (/dev/sda3 is the current root filesystem) # chcp ss /dev/sda3 7591068 # mount /dev/sda3 /mnt/x -o ro,cp=7591068 # diff -burN /etc/adjtime /mnt/x/etc/adjtime | diffstat adjtime | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) so far so good. However! # cp etc/adjtime /etc cp: `etc/adjtime' and `/etc/adjtime' are the same file and it did /not/ copy the original version over the new file. The thing is, till recently the `diff' would also (errorously!) not report difference between those two files, because it relied on comparing device and inode numbers. If those matched, the files must be the same file. Just like pointer equality in C programming language: if two objects are located at the same address (pointer equality), they are the same object. MVFS (a ClearCase thingie) and NILFS2 break that; diff now contains special workaround because of MVFS. But some other utilities do not. >From diff's sources: > POSIX says that two files are identical if st_ino and st_dev are > the same, but many file systems incorrectly assign the same (device, > inode) pair to two distinct files, including: > > ((short list: Linux NFS, Network Appliance NFS, MVFS)) Please consider fixing that: either report different inode numbers on mounted snapshots, or use different device numbers for mounted snapshots. The later could make more sense -- a snapshot of filesystem is a much different entity than the current state -- and also could be way easier to implement in kernel without changing filesystem format. Before any fix is ready, a manual workaround is possible, by using loop device: coil!root!/mnt # losetup -f -v /dev/sda3 Loop device is /dev/loop0 coil!root!/mnt # mount /dev/loop0 /mnt/x -o cp=7591068,ro (now /dev/loop0 mounted at /mnt/x has different device ID than the root filesystem at /dev/sda3) coil!root!~ # cp /mnt/x/etc/adjtime /etc/adjtime (worked!) Regards, -- dexen deVries [[[↓][→]]] For example, if the first thing in the file is: <?kzy irefvba="1.0" rapbqvat="ebg13"?> an XML parser will recognize that the document is stored in the traditional ROT13 encoding. (( Joe English, http://www.flightlab.com/~joe/sgml/faq-not.txt )) -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
