zbd: Add support for zoneskip option

zbd: Add support for zoneskip option

To speed up device tests (performance and or quality validation) of very
large capacity block devices such as SMR disks, it is useful to allow
skipping some block ranges for sequential workloads. While the
zonemode=stridded implements such feature, it does not allow controlling
read operations in partially written zones of zoned block devices (i.e.
prevent reads after a zone write pointer) and can result in IO errors
if executed on a zoned block devices with zones already written.

To solve this problem, add support for the zoneskip option with
zonemode=zbd, allowing a sequential workload to skip zoneskip bytes once
a zone has been fully written or its data has been read. The zoneskip
option is ignored for random workloads.

For read workloads, zone skipping takes into account the read_beyond_wp
option to switch zone either when all valid data in the zone is read
(read_beyond_wp=0) or the entire zone has been read (read_beyond_wp=1).

Add test47 to t/zbd/test-zbd-support to test that zoneskip invalid
values are handled correctly.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>