On 18/08/2021 08:38, Ming Lei wrote:

On Mon, Aug 09, 2021 at 10:29:35PM +0800, John Garry wrote:

quoted

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<redacted>
---
  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);

Hi Ming,

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

Sure, actually most versions of init_request callback don't use 
hctx_idx. Or numa_node arg.

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

Yeah, I did consider that. hctx_idx is an unsigned, and I generally 
don't like -1U - but that's no big deal. But I also didn't like how it 
relies on the driver init_request callback to check the value, which 
changes the semantics.

Obviously we don't add new versions of init_request for new block 
drivers which use shared sbitmap everyday, and any new ones would get it 
right.

I suppose I can go the way you suggest - I just thought that this method 
was neat as well.

Thanks,
John