[virtio-comment] virtio_blk_req.data size - Section 5.2.6 - version 1.1 draft 01

[virtio-comment] virtio_blk_req.data size - Section 5.2.6 - version 1.1 draft 01

[Savir, Gil]

In version 1.1 draft 01 - Section 5.2.6 - struct virtio_blk_req definition:

Data field is defined as array of 512 Byte entries as follows:
	u8 data[][512];
It makes sense for IN and OUT requests, since defined for read/write sizes that are 512 Bytes multiplication.
However, it is confusing when used for DISCARD or WRITE_ZEROES requests, since virtio_blk_discard_write_zeroes struct size is 16 Bytes.

Is implying that DISCARD and WRITE_ZEROES requests must use data-field sizes that are 512 Bytes multiplication as well?

If yes, than the device can't tell how many virtio_blk_discard_write_zeroes structs reside within data-field. In that case - indication for number of virtio_blk_discard_write_zeroes structs needs to be added.

If not, then I suggest to add to the spec clarification, that for DISCARD or WRITE_ZEROES requests, data-field is not required to be with size that is 512 Bytes multiplication.


Thanks,
Gil


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Re: [virtio-comment] virtio_blk_req.data size - Section 5.2.6 - version 1.1 draft 01

[Michael S. Tsirkin]

On Tue, Mar 05, 2019 at 04:18:10PM +0000, Savir, Gil wrote:
> In version 1.1 draft 01 - Section 5.2.6 - struct virtio_blk_req definition:
> 
> Data field is defined as array of 512 Byte entries as follows:
> 	u8 data[][512];
> It makes sense for IN and OUT requests, since defined for read/write sizes that are 512 Bytes multiplication.
> However, it is confusing when used for DISCARD or WRITE_ZEROES requests, since virtio_blk_discard_write_zeroes struct size is 16 Bytes.
> 
> Is implying that DISCARD and WRITE_ZEROES requests must use data-field sizes that are 512 Bytes multiplication as well?
> 
> If yes, than the device can't tell how many virtio_blk_discard_write_zeroes structs reside within data-field. In that case - indication for number of virtio_blk_discard_write_zeroes structs needs to be added.
> 
> If not, then I suggest to add to the spec clarification, that for DISCARD or WRITE_ZEROES requests, data-field is not required to be with size that is 512 Bytes multiplication.
> 
> 
> Thanks,
> Gil
> 

Thanks for the report.

I think this was resolved as part of resolution of
https://github.com/oasis-tcs/virtio-spec/issues/34


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Re: [virtio-comment] virtio_blk_req.data size - Section 5.2.6 - version 1.1 draft 01

[Stefan Hajnoczi]

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On Mon, Mar 18, 2019 at 06:44:48PM -0400, Michael S. Tsirkin wrote:
> On Tue, Mar 05, 2019 at 04:18:10PM +0000, Savir, Gil wrote:
> > In version 1.1 draft 01 - Section 5.2.6 - struct virtio_blk_req definition:
> > 
> > Data field is defined as array of 512 Byte entries as follows:
> > 	u8 data[][512];
> > It makes sense for IN and OUT requests, since defined for read/write sizes that are 512 Bytes multiplication.
> > However, it is confusing when used for DISCARD or WRITE_ZEROES requests, since virtio_blk_discard_write_zeroes struct size is 16 Bytes.
> > 
> > Is implying that DISCARD and WRITE_ZEROES requests must use data-field sizes that are 512 Bytes multiplication as well?
> > 
> > If yes, than the device can't tell how many virtio_blk_discard_write_zeroes structs reside within data-field. In that case - indication for number of virtio_blk_discard_write_zeroes structs needs to be added.
> > 
> > If not, then I suggest to add to the spec clarification, that for DISCARD or WRITE_ZEROES requests, data-field is not required to be with size that is 512 Bytes multiplication.
> > 
> > 
> > Thanks,
> > Gil
> > 
> 
> Thanks for the report.
> 
> I think this was resolved as part of resolution of
> https://github.com/oasis-tcs/virtio-spec/issues/34

Hi,
This was addressed by
https://github.com/oasis-tcs/virtio-spec/issues/32.

Stefan

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