On 13-Oct-09, at 18:49, Kazuya Mio wrote:
2009/10/10 2:20, Andreas Dilger wrote::
On 8-Oct-09, at 02:04, Kazuya Mio wrote:
EXT4_IOC_MOVE_EXT changes donor file data, but doesn't update
ctime/mtime. This patch fixes this problem.
I would argue that just migrating the file data shouldn't update the
ctime/mtime. Those are used to determine if the file has changed
in some way, usually for the purpose of backup. Migrating the data
does not change anything from user-space POV and shouldn't force a
new backup of the file.
EXT4_IOC_MOVE_EXT always changes the original actual contents of
donor file
if orig file and donor file aren't the same. It may be that some of
user-space implementations hide such a changing. For example, e4defrag
unlinks the donor file, and removes it by decreasing reference count
after
calling EXT4_IOC_MOVE_EXT. But from the ioctl point of view,
EXT4_IOC_MOVE_EXT doesn't know whether donor file will be removed or
not,
so I think we should update ctime/mtime.
Maybe I am confused. Is EXT4_IOC_MOVE_EXT used for file
defragmentation?
I thought the goal of this ioctl was to copy the data from the donor
inode
to the target inode (using a new allocation in the target inode), and
then
once the whole donor file had been copied (defragmented) the target
extents
replace the entire donor file's extents?
In this model it would be OK to change the mtime/ctime of the _target_
file,
but when these extents move back to the donor file the mtime/ctime of
the donor
file should not be changed, I think, so that it does not force a full
backup.
If the caller has done something to change the actual data in the
donor file
it can always use utimes() to update the ctime/mtime, but it is not
possible
for userspace to revert the ctime after it has changed.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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