dm thin: fix to consistently zero-fill reads to unprovisioned blocks
dm thin: fix to consistently zero-fill reads to unprovisioned blocks

It was always intended that a read to an unprovisioned block will return
zeroes regardless of whether the pool is in read-only or read-write
mode.  thin_bio_map() was inconsistent with its handling of such reads
when the pool is in read-only mode, it now properly zero-fills the bios
it returns in response to unprovisioned block reads.

Eliminate thin_bio_map()'s special read-only mode handling of -ENODATA
and just allow the IO to be deferred to the worker which will result in
pool->process_bio() handling the IO (which already properly zero-fills
reads to unprovisioned blocks).

Reported-by: Eric Sandeen <d55521028c14e0f378be5444e4ea388161c0d7e7@redhat.com>
Signed-off-by: Joe Thornber <61d5fad70554ae22d57a37634e04f12f58acc678@redhat.com>
Signed-off-by: Mike Snitzer <85e533f2e78486213c4d69f71462342ec0c62734@redhat.com>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs