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Date:   Mon, 12 Jul 2021 09:32:33 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-scsi@vger.kernel.org, Sagi Grimberg <sagi@grimberg.me>,
        Daniel Wagner <dwagner@suse.de>,
        Wen Xiong <wenxiong@us.ibm.com>,
        John Garry <john.garry@huawei.com>,
        Hannes Reinecke <hare@suse.de>,
        Keith Busch <kbusch@kernel.org>,
        Damien Le Moal <damien.lemoal@wdc.com>
Subject: Re: [PATCH V3 02/10] blk-mq: Introduce blk_mq_dev_map_queues
Message-ID: <20210712073233.GB12347@lst.de>
References: <20210709081005.421340-1-ming.lei@redhat.com> <20210709081005.421340-3-ming.lei@redhat.com>
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> +	/*
> +	 * fallback to default mapping if driver doesn't provide
> +	 * get_queue_affinity callback
> +	 */
> +	if (!get_queue_affinity) {
> +		fallback = true;
> +		goto fallback;
> +	}
> +
> +	for (queue = 0; queue < qmap->nr_queues; queue++) {
> +		mask = get_queue_affinity(dev_data, dev_off, queue);
> +		if (!mask)
> +			goto fallback;
> +
> +		for_each_cpu(cpu, mask)
> +			qmap->mq_map[cpu] = qmap->queue_offset + queue;
> +	}
> +
> +	return 0;
> +
> +fallback:
> +	if (!fallback) {
> +		WARN_ON_ONCE(qmap->nr_queues > 1);
> +		blk_mq_clear_mq_map(qmap);
> +		return 0;
> +	}
> +	return blk_mq_map_queues(qmap);

Please remove the NULL get_affinity case and let the callers handle
the fallback.  Also I think it makes sense to leave the !mask fallback
case to the callers as well to simplify the calling conventions.