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Date:   Wed, 15 Jun 2022 08:08:51 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Bart Van Assche <bvanassche@acm.org>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 3/3] block: Specify the operation type when calling
 blk_mq_map_queue()
Message-ID: <20220615060851.GE22115@lst.de>
References: <20220614175725.612878-1-bvanassche@acm.org> <20220614175725.612878-4-bvanassche@acm.org> <YqkoWUjOPgpqzn4E@T590>
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On Wed, Jun 15, 2022 at 08:31:21AM +0800, Ming Lei wrote:
> > -	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, 0, ctx);
> > +	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, REQ_OP_WRITE, ctx);
> 
> The change itself doesn't make a difference, since both results in choosing
> HCTX_TYPE_DEFAULT, but passing REQ_OP_WRITE is a bit misleading.

Well, the argument is an operationm so we better pass in a correct
operation (at some point we should look into a __bitwise annotation
or similar to make it clean).  And as 0 is REQ_OP_READ, we will end
up with the HCTX_TYPE_READ hctx IFF someone configures read queues
and uses an sq only schedule.  Which is a completely stupid but
possible setup.