Re: [PATCH 1/8] blk-mq: add blk_mq_alloc_request_hctx

[Jens Axboe]

On 06/06/2016 03:21 PM, Christoph Hellwig wrote:

From: Ming Lin <min...@ssi.samsung.com>

For some protocols like NVMe over Fabrics we need to be able to send
initialization commands to a specific queue.

Based on an earlier patch from Christoph Hellwig <h...@lst.de>.

Signed-off-by: Ming Lin <min...@ssi.samsung.com>
Signed-off-by: Christoph Hellwig <h...@lst.de>
---
  block/blk-mq.c         | 33 +++++++++++++++++++++++++++++++++
  include/linux/blk-mq.h |  2 ++
  2 files changed, 35 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 29cbc1b..7bb45ed 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -266,6 +266,39 @@ struct request *blk_mq_alloc_request(struct request_queue 
*q, int rw,
  }
  EXPORT_SYMBOL(blk_mq_alloc_request);

+struct request *blk_mq_alloc_request_hctx(struct request_queue *q, int rw,
+               unsigned int flags, unsigned int hctx_idx)
+{
+       struct blk_mq_hw_ctx *hctx;
+       struct blk_mq_ctx *ctx;
+       struct request *rq;
+       struct blk_mq_alloc_data alloc_data;
+       int ret;
+
+       ret = blk_queue_enter(q, flags & BLK_MQ_REQ_NOWAIT);
+       if (ret)
+               return ERR_PTR(ret);
+
+       hctx = q->queue_hw_ctx[hctx_idx];
+       ctx = __blk_mq_get_ctx(q, cpumask_first(hctx->cpumask));
+
+       blk_mq_set_alloc_data(&alloc_data, q, flags, ctx, hctx);
+
+       rq = __blk_mq_alloc_request(&alloc_data, rw);
+       if (!rq && !(flags & BLK_MQ_REQ_NOWAIT)) {
+               __blk_mq_run_hw_queue(hctx);
+
+               rq =  __blk_mq_alloc_request(&alloc_data, rw);
+       }

Why are we duplicating this code here? If NOWAIT isn't set, then we'll
always return a request. bt_get() will run the queue for us, if it needs
to. blk_mq_alloc_request() does this too, and I'm guessing that code was
just copied. I'll fix that up. Looks like this should just be:

        rq = __blk_mq_alloc_request(&alloc_data, rw);
        if (rq)
                return rq;

        blk_queue_exit(q);
        return ERR_PTR(-EWOULDBLOCK);

for this case.

--
Jens Axboe