linux-kernel - Re: [PATCH v2 08/11] blk-mq: Add blk_mq_ops.init_request_no

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Date:   Wed, 18 Aug 2021 15:38:51 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     axboe@...nel.dk, jejb@...ux.ibm.com, martin.petersen@...cle.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, kashyap.desai@...adcom.com,
        hare@...e.de
Subject: Re: [PATCH v2 08/11] blk-mq: Add blk_mq_ops.init_request_no_hctx()

On Mon, Aug 09, 2021 at 10:29:35PM +0800, John Garry wrote:
> Add a variant of the init_request function which does not pass a hctx_idx
> arg.
> 
> This is important for shared sbitmap support, as it needs to be ensured for
> introducing shared static rqs that the LLDD cannot think that requests
> are associated with a specific HW queue.
> 
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>  block/blk-mq.c         | 15 ++++++++++-----
>  include/linux/blk-mq.h |  7 +++++++
>  2 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f14cc2705f9b..4d6723cfa582 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2427,13 +2427,15 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
>  static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
>  			       unsigned int hctx_idx, int node)
>  {
> -	int ret;
> +	int ret = 0;
>  
> -	if (set->ops->init_request) {
> +	if (set->ops->init_request)
>  		ret = set->ops->init_request(set, rq, hctx_idx, node);
> -		if (ret)
> -			return ret;
> -	}
> +	else if (set->ops->init_request_no_hctx)
> +		ret = set->ops->init_request_no_hctx(set, rq, node);

The only shared sbitmap user of SCSI does not use passed hctx_idx, not
sure we need such new callback.

If you really want to do this, just wondering why not pass '-1' as
hctx_idx in case of shared sbitmap?


Thanks,
Ming