[PATCH V2] xfstests 249: use -F option for xfs_io

[Alex Elder]

On Wed, 2011-03-23 at 11:03 -0500, Eric Sandeen wrote:
> Test 249 was appearing to pass on ext4, but it wasn't really
> exercising the test due to lack of "-F" in the xfs_io arguments.
> 
> Without -F the files were created (oddly enough); neither pwrite
> nor sendfile were executed, and the diff of the two (empty)
> files passed, resulting in a passed test without testing anything.
> 
> So add the -F, capture the output, and test the result of each
> xfs_io invocation.
> 
> Also, when it fails, the diff output is huge.  Make diff silent,
> but describe the diff failure and exit.
> 
> Signed-off-by: Eric Sandeen <sandeen at redhat.com>

Looks good.

Reviewed-by: Alex Elder <aelder at sgi.com>