id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	launchpad_bug
1228	backupdb and ext4 i_version/generation xattributes	warner	warner	"I recently learned that several linux filesystems can track
version/generation numbers for local files. We could use this
information in the backupdb to improve the speed+reliability of
detecting files that have not been modified since the last time we
did a backup.

{{{lsattr -v FOO.txt}}} shows a ""version/generation number"", and
probably works for even old ext2 filesystems.

[http://www.spinics.net/lists/linux-fsdevel/msg33753.html this] and
[http://linux-ima.sourceforge.net/ this] talk about ""mounting a
filesystem with {{{i_version}}} support"", and suggests that the
following ext4 extended-attributes will become available:

 * {{{file.crtime}}} - actual file creation time
 * {{{file.i_generation}}} - inode generation number
 * {{{file.i_version}}} (""directories only"") - inode data version number

It's not yet clear to me what information is really available, or
how one might get to it (especially from python), but this ticket is to remind me that ""tahoe
backup"" would be a lot better if we could quickly and reliably
determine that a file had not changed. The filesize+timestamp
heuristic is useful, but it'd be nice to be able to do better. A
real generation number would be ideal, if the kernel promises to
update it reliably. A kernel-maintained hash of the filesystem contents would be great too (it would let us detect renames without reading the file contents).
"	enhancement	new	normal	undecided	code-encoding	1.8.0		performance