linux-kernel - Re: [PATCH V5 16/16] block: ublk_drv: apply io_uring FUSED

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Date:   Wed, 29 Mar 2023 10:57:53 +0800
From:   Ziyang Zhang <ZiyangZhang@...ux.alibaba.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>,
        Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>,
        Bernd Schubert <bschubert@....com>,
        Pavel Begunkov <asml.silence@...il.com>,
        io-uring@...r.kernel.org, Stefan Hajnoczi <stefanha@...hat.com>,
        linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH V5 16/16] block: ublk_drv: apply io_uring FUSED_CMD for
 supporting zero copy

On 2023/3/28 23:09, Ming Lei wrote:
> Apply io_uring fused command for supporting zero copy:
> 

[...]

>  
> @@ -1374,7 +1533,12 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
>  	if (!ubq || ub_cmd->q_id != ubq->q_id)
>  		goto out;
>  
> -	if (ubq->ubq_daemon && ubq->ubq_daemon != current)
> +	/*
> +	 * The fused command reads the io buffer data structure only, so it
> +	 * is fine to be issued from other context.
> +	 */
> +	if ((ubq->ubq_daemon && ubq->ubq_daemon != current) &&
> +			(cmd_op != UBLK_IO_FUSED_SUBMIT_IO))
>  		goto out;
>  

Hi Ming,

What is your use case that fused io_uring cmd is issued from another thread?
I think it is good practice to operate one io_uring instance in one thread
only.

Regards,
Zhang