On Tue, Jun 26, 2007 at 11:34:13AM -0400, Andreas Dilger wrote:

On Jun 26, 2007  16:02 +0530, Amit K. Arora wrote:

quoted

On Mon, Jun 25, 2007 at 03:46:26PM -0600, Andreas Dilger wrote:

quoted

Can you clarify - what is the current behaviour when ENOSPC (or some other
error) is hit?  Does it keep the current fallocate() or does it free it?

Currently it is left on the file system implementation. In ext4, we do
not undo preallocation if some error (say, ENOSPC) is hit. Hence it may
end up with partial (pre)allocation. This is inline with dd and
posix_fallocate, which also do not free the partially allocated space.

Since I believe the XFS allocation ioctls do it the opposite way (free
preallocated space on error) this should be encoded into the flags.
Having it "filesystem dependent" just means that nobody will be happy.

No, XFs does not free preallocated space on error. it is up to the
application to clean up.

What I mean is that any data read from the file should have the "appearance"
of being zeroed (whether zeroes are actually written to disk or not).  What
I _think_ David is proposing is to allow fallocate() to return without
marking the blocks even "uninitialized" and subsequent reads would return
the old data from the disk.

Correct, but for swap files that's not an issue - no user should be able
too read them, and FA_MKSWAP would really need root privileges to execute.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group