EX-6127 llite: DIO fallback on compressed files

EX-6127 llite: DIO fallback on compressed files

Fully supporting direct I/O on compressed files is tricky
because we cannot pull the full chunk in to the page cache
(because there is no page cache for DIO).

So instead we fall back to buffered I/O for DIO on
compressed files.

This patch adds the check and a test for this.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I8224ef9b8ad1d912d8a11eccad37d3dff8dd8498
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51200
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>