Re: [virtio-dev] [PATCH v6] virtio-blk: add zoned block device specification

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Sun, Sep 04, 2022 at 12:56:01PM -0400, Dmitry Fomichev wrote:
> @@ -4746,7 +4930,15 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
>          le32 reserved;
>          le64 sector;
>          u8 data[];
> -        u8 status;
> +        union {
> +                u8 status;
> +
> +                struct {
> +                        u8 status;
> +                        u8 reserved[7];
> +                        le64 append_sector;
> +                } zone_append_in_hdr;
> +        };

If a zone append request is sent to a device without VIRTIO_BLK_F_ZONED,
then should the device store VIRTIO_BLK_S_UNSUPP to status or to
zone_append_in_hdr.status?

(I think the answer is status.)

It seems simpler to avoid this problem and instead define:

  struct virtio_blk_zone_append_in_hdr {
      le64 append_sector;
  }

and say that zone append requests have this struct *before* struct
virtio_blk_in_hdr. So the layout is:

  le32 type;
  le32 reserved;
  le64 sector;
  u8 data[];
  le64 append_sector;
  u8 status;

That way the location of the status field does not change, it's always
the last byte.

Stefan

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