block: ublk: check IO buffer based on flag need_get_data

block: ublk: check IO buffer based on flag need_get_data

Currently, uring_cmd with UBLK_IO_FETCH_REQ or
UBLK_IO_COMMIT_AND_FETCH_REQ is always checked whether
userspace server has provided IO buffer even flag
UBLK_F_NEED_GET_DATA is configured.

This is a excessive check. If UBLK_F_NEED_GET_DATA is
configured, FETCH_RQ doesn't need to provide IO buffer;
COMMIT_AND_FETCH_REQ also doesn't need to do that if
the IO type is not READ.

Check ub_cmd->addr together with ublk_need_get_data()
and IO type in ublk_ch_uring_cmd().

With this fix, userspace server doesn't need to preserve
buffers for every ublk_io when flag UBLK_F_NEED_GET_DATA
is configured, in order to save memory.

Signed-off-by: Liu Xiaodong <xiaodong.liu@intel.com>
Fixes: c86019ff75c1 ("ublk_drv: add support for UBLK_IO_NEED_GET_DATA")
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230210141356.112321-1-xiaodong.liu@intel.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>