From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [PATCH v4] virtio_blk: add DISCARD and WRIET ZEROES commands
	support
Date: Thu, 31 May 2018 11:30:47 +0100
Message-ID: <20180531103047.GB27838@stefanha-x1.localdomain>
References: <1527558144-3825-1-git-send-email-changpeng.liu@intel.com>
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To: Changpeng Liu <changpeng.liu@intel.com>
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On Tue, May 29, 2018 at 09:42:24AM +0800, Changpeng Liu wrote:
>  	num = blk_rq_map_sg(hctx->queue, req, vbr->sg);
>  	if (num) {
> -		if (rq_data_dir(req) == WRITE)
> +		if (rq_data_dir(req) == WRITE || type == VIRTIO_BLK_T_DISCARD ||
> +		    type == VIRTIO_BLK_T_WRITE_ZEROES)
>  			vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_OUT);

The VIRTIO specification says:

  The type of the request is either a read (VIRTIO_BLK_T_IN), a write
  (VIRTIO_BLK_T_OUT), a discard (VIRTIO_BLK_T_DISCARD), a write zeroes
  (VIRTIO_BLK_T_WRITE_ZEROES) or a flush (VIRTIO_BLK_T_FLUSH).

But this patch actually uses VIRTIO_BLK_T_DISCARD | VIRTIO_BLK_T_OUT or
VIRTIO_BLK_T_WRITE_ZEROES | VIRTIO_BLK_T_OUT.  "either A or B" is
exclusive, it does not mean "A and B".

Can you clarify whether the spec needs to be changed or what the purpose
of ORing in the VIRTIO_BLK_T_OUT bit is?

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