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Message-ID: <cacc3f7b-c8be-0f72-1c52-562c15b468a4@huawei.com>
Date:   Tue, 22 Mar 2022 11:33:17 +0000
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Subject: Re: [PATCH 01/11] blk-mq: Add blk_mq_init_queue_ops()
To:     Christoph Hellwig <hch@lst.de>
CC:     <axboe@kernel.dk>, <damien.lemoal@opensource.wdc.com>,
        <bvanassche@acm.org>, <jejb@linux.ibm.com>,
        <martin.petersen@oracle.com>, <ming.lei@redhat.com>,
        <hare@suse.de>, <chenxiang66@hisilicon.com>,
        <linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-ide@vger.kernel.org>, <linux-scsi@vger.kernel.org>,
        <dm-devel@redhat.com>, <beanhuo@micron.com>
References: <1647945585-197349-1-git-send-email-john.garry@huawei.com>
 <1647945585-197349-2-git-send-email-john.garry@huawei.com>
 <20220322111848.GA29270@lst.de>
From:   John Garry <john.garry@huawei.com>
In-Reply-To: <20220322111848.GA29270@lst.de>
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On 22/03/2022 11:18, Christoph Hellwig wrote:
> On Tue, Mar 22, 2022 at 06:39:35PM +0800, John Garry wrote:
>> Add an API to allocate a request queue which accepts a custom set of
>> blk_mq_ops for that request queue.
>>
>> The reason which we may want custom ops is for queuing requests which we
>> don't want to go through the normal queuing path.
> 
> Eww.  I really do not think we should do separate ops per queue, as that
> is going to get us into a deep mess eventually.
> 

Yeah... so far (here) it works out quite nicely, as we don't need to 
change the SCSI blk mq ops nor allocate a scsi_device - everything is 
just separate.

The other method mentioned previously was to add the request "reserved" 
flag and add new paths in scsi_queue_rq() et al to handle this, but that 
gets messy.

Any other ideas ...?

Cheers,
John