options: add a parsing function for an additional cmdprio_bssplit format

options: add a parsing function for an additional cmdprio_bssplit format

The cmdprio_bssplit ioengine option for io_uring/libaio is currently parsed
using split_parse_ddir(). While this function works fine for parsing the
existing cmdprio_bssplit entry format, it forces every cmdprio_bssplit
entry to use the priority defined by cmdprio and cmdprio_class. This means
that there will only ever be at most two different priority values used in
the job.

To enable us to use more than two different priority values, add a new
parsing function, split_parse_prio_ddir(), that will support parsing the
existing cmdprio_bssplit entry format (blocksize/percentage), and a new
cmdprio_bssplit entry format (blocksize/percentage/prioclass/priolevel).

Since IO engines can be compiled as plugins, having the parse function in
options.c avoids potential problems with ioengines having different
versions of the same parsing function.

A follow up patch will change to the new parsing function.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Link: https://lore.kernel.org/r/20220203192814.18552-8-Niklas.Cassel@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>