Hi Jens

On 11/13/18 11:22 AM, Jens Axboe wrote:

On 11/12/18 2:23 AM, Jianchao Wang wrote:

quoted

Merge blk_mq_try_issue_directly and __blk_mq_try_issue_directly
into one interface to unify the interfaces to issue requests
directly. The merged interface takes over the requests totally,
it could insert, end or do nothing based on the return value of
.queue_rq and 'bypass' parameter. Then caller needn't any other
handling any more.

To make code clearer, introduce new helpers enum mq_issue_decision
and blk_mq_make_decision to decide how to handle the non-issued
requests.

Signed-off-by: Jianchao Wang <redacted>
---
 block/blk-mq.c | 108 +++++++++++++++++++++++++++++++++------------------------
 1 file changed, 63 insertions(+), 45 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 364a53f..48b7a7c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -1766,77 +1766,95 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 	return ret;
 }
 
-static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+enum mq_issue_decision {
+	MQ_ISSUE_INSERT_QUEUE,
+	MQ_ISSUE_END_REQUEST,
+	MQ_ISSUE_DO_NOTHING,
+};
+
+static inline enum mq_issue_decision
+	blk_mq_make_dicision(blk_status_t ret, bool bypass)
+{
+	enum mq_issue_decision dec;
+
+	switch(ret) {
+	case BLK_STS_OK:
+		dec = MQ_ISSUE_DO_NOTHING;
+		break;
+	case BLK_STS_DEV_RESOURCE:
+	case BLK_STS_RESOURCE:
+		dec = bypass ? MQ_ISSUE_DO_NOTHING : MQ_ISSUE_INSERT_QUEUE;
+		break;
+	default:
+		dec = bypass ? MQ_ISSUE_DO_NOTHING : MQ_ISSUE_END_REQUEST;
+		break;
+	}
+
+	return dec;
+}

You seem to mix and match decision and dicision, the former is the
right spelling.

Oops, it's my bad that not find this even in V5 respin.

But more importantly, not sure I like where this is going, wrapping
the return value in some other status code. That also makes it a bit
fragile in terms of adding other status codes, another spot to update.
Like the decent distinction between RESOURCE and DEV_RESOURCE.

Maybe it is cleaner to just handle this in the caller still?

Actually enum mq_issue_decision is introduced to reduce the depth of
'if' branch. And it is indeed not good to introduce another status value.

I will discard enum mq_issue_decision and blk_mq_make_decision in next version.

Thanks
Jianchao