Re: [PATCH] block: ublk: check IO buffer based on flag need_get_data

[Ming Lei]

On Fri, Feb 10, 2023 at 09:13:56AM -0500, Liu Xiaodong wrote:
> 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@xxxxxxxxx>

Good catch!

Fixes: c86019ff75c1 ("ublk_drv: add support for UBLK_IO_NEED_GET_DATA")
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>

Thanks,
Ming