[PATCH 04/17] block: add a blk_steal_bios helper

[Max Gurtovoy]

On 10/23/2017 5:51 PM, Christoph Hellwig wrote:
> This helpers allows to bounce steal the uncompleted bios from a request so
> that they can be reissued on another path.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
> ---
>   block/blk-core.c       | 20 ++++++++++++++++++++
>   include/linux/blkdev.h |  2 ++
>   2 files changed, 22 insertions(+)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index b8c80f39f5fe..e804529e65a5 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -2767,6 +2767,26 @@ struct request *blk_fetch_request(struct request_queue *q)
>   }
>   EXPORT_SYMBOL(blk_fetch_request);
>   
> +/*
> + * Steal bios from a request.  The request must not have been partially
> + * completed before.
> + */

Maybe we can add to the comment that "list" is the destination for the 
stolen bio.

> +void blk_steal_bios(struct bio_list *list, struct request *rq)
> +{
> +	if (rq->bio) {
> +		if (list->tail)
> +			list->tail->bi_next = rq->bio;
> +		else
> +			list->head = rq->bio;
> +		list->tail = rq->biotail;

if list->tail != NULL don't we lose the "list->tail->bi_next = rq->bio;" 
assignment after assigning "list->tail = rq->biotail;" ?

> +	}
> +
> +	rq->bio = NULL;

we can add this NULL assignment inside the big "if", but I'm not sure 
regarding the next 2 assignments.
Anyway not a big deal.

> +	rq->biotail = NULL;
> +	rq->__data_len = 0;
> +}
> +EXPORT_SYMBOL_GPL(blk_steal_bios);
> +