Re: [PATCH 02/21] block: add flag for internal commands

[John Garry <john.garry@huawei.com>]

On 09/07/2020 21:02, Jens Axboe wrote:
> On 7/8/20 3:27 AM, John Garry wrote:
>> On 03/07/2020 14:01, Hannes Reinecke wrote:
>>
>> +linux-block
>>
>> I figure that linux-block should be cc'ed here
>>
>>> Some drivers require to allocate requests for internal command
>>> submission. These request will never be passed through the block
>>> layer, but nevertheless require a valid tag to avoid them clashing
>>> with normal I/O commands.
>>> This patch adds a new request flag REQ_INTERNAL to mark such
>>> requests and a terminates any such commands in blk_execute_rq_nowait()
>>> with a WARN_ON_ONCE to signal such an invalid usage.

So if these requests will never be passed through the block layer - as 
you say - then why add a check for this? Surely you will find out in 
nasty and obvious ways that it should be done.

Thanks,
John

>>>
>>> Signed-off-by: Hannes Reinecke <hare@suse.de>
>>> ---
>>>    block/blk-exec.c          | 5 +++++
>>>    include/linux/blk_types.h | 2 ++
>>>    include/linux/blkdev.h    | 5 +++++
>>>    3 files changed, 12 insertions(+)
>>>
>>> diff --git a/block/blk-exec.c b/block/blk-exec.c
>>> index 85324d53d072..6869877e0d21 100644
>>> --- a/block/blk-exec.c
>>> +++ b/block/blk-exec.c
>>> @@ -55,6 +55,11 @@ void blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk,
>>>    	rq->rq_disk = bd_disk;
>>>    	rq->end_io = done;
>>>    
>>> +	if (WARN_ON_ONCE(blk_rq_is_internal(rq))) {
>>> +		blk_mq_end_request(rq, BLK_STS_NOTSUPP);
>>> +		return;
>>> +	}
>>> +
>>>    	blk_account_io_start(rq);
> 
> The whole concept seems very odd, and then there's this seemingly
> randomly placed check and error condition. As I haven't seen the
> actual use case for this, hard to make suggestions though.
>