On Fri, Mar 05, 2010 at 03:40:49PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> If the file being defragmented has attributes, then fsr puts a dummy
> attribute on the temporary file to try to ensure that the inode
> attribute fork offset is set correctly. This works perfectly well
> for the old style of attributes that use a fixed fork offset - the
> presence of any attribute of any size or shape will result in fsr
> doing the correct thing.
> However, for attr2 filesystems, the attribute fork offset is
> dependent on the size and shape of both the data and attribute
> forks. Hence setting a small attribute on the file does not
> guarantee that the two inodes have the same fork offset and
> therefore compatible for a data fork swap.
> This patch improves the attribute fork handling of fsr. It checks
> the filesystem version to see if the old style attributes are in
> use, and if so uses the current method.
> If attr2 is in use, fsr uses bulkstat output to determine what the
> fork offset is. If the attribute fork offsets differ then fsr will
> try to create attributes that will result in the correct offset. If
> that fails, or the attribute fork is too large, it will give up and just
> attempt the swap.
> This fork offset value in bulkstat new functionality in the kernel,
> so if there are attributes and a zero fork offset, then the kernel
> does not support this feature and we simply fall back to the existing,
> less effective code.
Looks reasonable. It would be good to have a testcase for this in
xfsqa to verify this works.