From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Liu, Changpeng" <changpeng.liu@intel.com>
Subject: RE: [PATCH v4] virtio_blk: add DISCARD and WRIET ZEROES commands
	support
Date: Tue, 5 Jun 2018 00:55:19 +0000
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> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> Sent: Monday, June 4, 2018 6:03 PM
> To: Liu, Changpeng <changpeng.liu@intel.com>; Stefan Hajnoczi
> <stefanha@redhat.com>
> Cc: virtualization@lists.linux-foundation.org; cavery@redhat.com;
> jasowang@redhat.com; Wang, Wei W <wei.w.wang@intel.com>
> Subject: Re: [PATCH v4] virtio_blk: add DISCARD and WRIET ZEROES commands
> support
> 
> On 04/06/2018 06:14, Liu, Changpeng wrote:
> >>> But I believe the specification says VIRTIO_BLK_T_OUT means direction, so
> >>> OR the two bits together should compliance with the specification.
> >> I cannot find that in the specification:
> >>
> >>   http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-
> >> 2020002
> >>
> >> and it would contradict the "The type of the request is either ... or
> >> ..." wording that I quoted from the spec above.
> >>
> >> If you do find something in the spec, please let me know and we can
> >> figure out how to make the spec consistent.
> >
> > I saw comments from file linux/usr/include/uapi/linux/virtio_blk.h, which says
> > VIRTIO_BLK_T_OUT may be combined with other commands and means direction,
> > the specification does not have such description.
> 
> I don't think it is in the specification indeed (however, 11 and 13 were
> chosen so that VIRTIO_BLK_T_OUT can still indicate direction).
Correct, we don't need to OR VIRTIO_BLK_T_OUT again for DISCARD and WRITE ZEROES commands.
I'll remove it in next patch set.
> 
> Paolo