generic/158: test dedupe with destination offset past EOF

generic/158: test dedupe with destination offset past EOF

We were testing when the source file offset starts at EOF or beyond,
but not when the destination offset is beyond EOF or when the
destination offset is smaller than EOF but destination offset plus
dedup length is greater than EOF.

This is motivated by a bug in btrfs' extent_same (dedup) ioctl where
we allowed the destination offset to start at EOF and beyond (and
destination offset + length beyond EOF) for the case where the source
and destination files are the same (was not allowed for different
files used as source and destination). This also made the file's
metadata inconsistent when the dedup operation succeeded, which
happened when the source range corresponded to a file hole, prealloc
extent or a data extent filled with zeroes.

The btrfs issue is fixed by the following patch for the linux kernel:

  "Btrfs: fix extent_same allowing destination offset beyond i_size"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
[darrick.wong@oracle.com: fix merge conflicts with latest reflink patchbomb]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>