EX-7601 llite: round LDLM lock requests to chunk

EX-7601 llite: round LDLM lock requests to chunk

When we do IO with compression, we may need to 'fill' the
compression chunk, reading up pages which have already been
written to storage, so we can compress the whole chunk.

Doing this safely requires that any dlmlock we're using
always covers the full chunk.

The easiest way to do this is to round the entire locking
process to include leading or trailing compression chunks.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I3c365844561d0da909e6290f4b58ef2211c2d255
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51266
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>