Re: [PATCH V4 2/2] ublk_drv: add support for UBLK_IO_NEED_GET_DATA

[Ming Lei <ming.lei@redhat.com>]

On Thu, Jul 28, 2022 at 08:39:16PM +0800, ZiyangZhang wrote:
> UBLK_IO_NEED_GET_DATA is one ublk IO command. It is designed for a user
> application who wants to allocate IO buffer and set IO buffer address
> only after it receives an IO request from ublksrv. This is a reasonable
> scenario because these users may use a RPC framework as one IO backend
> to handle IO requests passed from ublksrv. And a RPC framework may
> allocate its own buffer(or memory pool).
> 
> This new feature (UBLK_F_NEED_GET_DATA) is optional for ublk users.
> Related userspace code has been added in ublksrv[1] as one pull request.
> 
> Test cases for this feature are added in ublksrv and all the tests pass.
> The performance result shows that this new feature does bring additional
> latency because one IO is issued back to ublk_drv once again to copy data
> from bio vectors to user-provided data buffer. UBLK_IO_NEED_GET_DATA is
> suitable for bigger block size such as 512B or 1MB.
> 
> [1] https://github.com/ming1/ubdsrv
> 
> Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks,
Ming