Re: [PATCH] virtio-blk: Add a VIRTIO_BLK_T_OUT_FUA request type

On Wed, May 7, 2025 at 8:30 AM Alberto Faria <[email protected]> wrote:
>
> This is a variant of the VIRTIO_BLK_T_OUT request type that further
> ensures the write becomes stable once the request completes, commonly
> known as a Force Unit Access (FUA) request.
>
> Also add a VIRTIO_BLK_F_OUT_FUA feature bit signaling support for this
> request type.

How does this interact with the writeback field? Presumably the value
of writeback is ignored by FUA commands, but it would be good to make
that explicit.

Also, the device requirements "write is considered volatile when it is
submitted"/"write becomes stable" section seems like it should be
updated to include FUA requests.

[...]
>
> +Drivers SHOULD NOT negotiate VIRTIO_BLK_F_OUT_FUA if they are incapable of
> +sending VIRTIO_BLK_T_OUT_FUA commands.

What harm would be caused if a driver accepts the FUA feature bit but
never sends a FUA command?

Thanks,
-- Daniel