Re: [PATCH 0/4] Fiemap, an extent mapping ioctl - round 2

[Andreas Dilger <adilger@sun.com>]

On Jun 27, 2008  23:21 -0500, Eric Sandeen wrote:
> even w/ metadata out of the way the ext4 extent format is still
> capped at 128M per extent right, even if they're contiguous.  Which led
> me to the little though experiment about hm, is this 1G file 1 extent or
> 8 and what should fiemap return...

The current FIEMAP code will return 8 extents, which mirrors the number
of physical extents on disk.  This could be important to the person
looking at the file, as it will be clear that there are too many
extents to fit into the inode and the extent tree will include an index
block.

I was a bit on the fence about this, but I agree with David that if
userspace has more information (e.g. all of the on-disk extent data)
it can always merge it, but it can't "un-merge" the data returned
from the kernel.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.