linux-kernel - Re: [PATCH 2/3] xen-blkfront: introduce blkif_set_queue

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Date:	Thu, 21 Jul 2016 17:44:37 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Roger Pau Monné <roger.pau@...rix.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
	konrad.wilk@...cle.com, jgross@...e.com
Subject: Re: [PATCH 2/3] xen-blkfront: introduce blkif_set_queue_limits()


On 07/21/2016 04:29 PM, Roger Pau Monné wrote:
> On Fri, Jul 15, 2016 at 05:31:48PM +0800, Bob Liu wrote:
>> blk_mq_update_nr_hw_queues() reset all queue limits to default which it's not
>> as xen-blkfront expected, introducing blkif_set_queue_limits() to reset limits
>> with initial correct values.
> 
> Hm, great, and as usual in Linux there isn't even a comment in the function 
> that explains what it is supposed to do, or what are the side-effects of 
> calling blk_mq_update_nr_hw_queues.
>  
>> Signed-off-by: Bob Liu <bob.liu@...cle.com>
>>
>>  drivers/block/xen-blkfront.c | 91 ++++++++++++++++++++++++--------------------
>>  1 file changed, 50 insertions(+), 41 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 032fc94..10f46a8 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -189,6 +189,8 @@ struct blkfront_info
>>  	struct mutex mutex;
>>  	struct xenbus_device *xbdev;
>>  	struct gendisk *gd;
>> +	u16 sector_size;
>> +	unsigned int physical_sector_size;
>>  	int vdevice;
>>  	blkif_vdev_t handle;
>>  	enum blkif_state connected;
>> @@ -913,9 +915,45 @@ static struct blk_mq_ops blkfront_mq_ops = {
>>  	.map_queue = blk_mq_map_queue,
>>  };
>>  
>> +static void blkif_set_queue_limits(struct blkfront_info *info)
>> +{
>> +	struct request_queue *rq = info->rq;
>> +	struct gendisk *gd = info->gd;
>> +	unsigned int segments = info->max_indirect_segments ? :
>> +				BLKIF_MAX_SEGMENTS_PER_REQUEST;
>> +
>> +	queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);
>> +
>> +	if (info->feature_discard) {
>> +		queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, rq);
>> +		blk_queue_max_discard_sectors(rq, get_capacity(gd));
>> +		rq->limits.discard_granularity = info->discard_granularity;
>> +		rq->limits.discard_alignment = info->discard_alignment;
>> +		if (info->feature_secdiscard)
>> +			queue_flag_set_unlocked(QUEUE_FLAG_SECDISCARD, rq);
>> +	}
> 
> AFAICT, at the point this function is called (in blkfront_resume), the 
> value of info->feature_discard is still from the old backend, maybe this 
> should be called from blkif_recover after blkfront_gather_backend_features?
> 

Thank you for pointing out, will be fixed.

-- 
Regards,
-Bob