block/parallels: read up to cluster end in one go

block/parallels: read up to cluster end in one go

Teach parallels_read() to do reads in coarser granularity than just a
single sector: if requested, read up to the cluster end in one go.

Signed-off-by: Roman Kagan <rkagan@parallels.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1430207220-24458-5-git-send-email-den@openvz.org
CC: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>