Re: [PATCH 2/3] xen-blkfront: introduce blkif_set_queue_limits()

["Roger Pau Monné" <roger.pau@citrix.com>]

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@oracle.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?

Roger.