"Michael S. Tsirkin" <> writes:
> TODO: we really should be more specific
> ---
> content.tex | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/content.tex b/content.tex
> index 3e7dcfc..2f467d5 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -344,7 +344,7 @@ addition, the specification for virtio_blk SCSI commands required
> intuiting field lengths from frame boundaries (see
>
\ref{sec:Device Types / Block Device / Device Operation / Legacy Interface: Device Operation}~\nameref{sec:Device Types / Block Device / Device Operation / Legacy Interface: Device Operation})
>
> -It is thus recommended that when using legacy interfaces, transitional
> +It is thus RECOMMENDED that when using legacy interfaces, transitional
> drivers be conservative in their assumptions, unless the
> VIRTIO_F_ANY_LAYOUT feature is accepted.
Yes, let's turn this into a requirement, but we'll need to do it for
each section. These requirements need to be in normative sections, too.
ie replace this with:
Thus the VIRTIO_F_ANY_LAYOUT feature was introduced to indicate that
no assumptions were made about framing. Requirements for
transitional drivers when this is not negotiated are included in each
device section.
Net:
When using legacy interfaces, transitional drivers which have not
negotiated VIRTIO_F_ANY_LAYOUT MUST use a single descriptor for the
struct virtio_net_hdr on both transmit and receive, with the network
data in the following descriptors. See \ref{sec:Basic Facilities of a
Virtio Device / Virtqueues / Message Framing}.
Block: (Replaces existing "Historically, devices assumed that...")
When using legacy interfaces, transitional drivers which have not
negotiated VIRTIO_F_ANY_LAYOUT:
\begin{itemize}
\item MUST use a single 8-byte descriptor containing \field{type},
\field{reseved} and \field{sector}, followed by descriptors
for \field{data}, then finally a separate 1-byte descriptor
for \field{status}.
\item For SCSI commands there are additional constraints.
\field{errors}, \field{data_len}, \field{sense_len} and
\field{residual} MUST reside in a single, separate
device-writable descriptor, \field{sense} MUST reside in a
single separate device-writable descriptor of size 96 bytes,
and \field{errors}, \field{data_len}, \field{sense_len} and
\field{residual} MUST reside a single separate
device-writable descriptor.
\end{itemize}
See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Message Framing}.
Console:
When using legacy interfaces, transitional drivers which have not
negotiated VIRTIO_F_ANY_LAYOUT MUST use only a single descriptor for
all buffers in the control receiveq and control transmitq.
Entropy: nothing
Memory Balloon Device: nothing (qemu always handled this correctly)
SCSI:
When using legacy interfaces, transitional drivers which have not
negotiated VIRTIO_F_ANY_LAYOUT MUST use a single descriptor for the
\field{lun}, \field{id}, \field{task_attr}, \field{prio},
\field{crn} and \field{cdb} fields, and MUST only use a single
descriptor for the \field{sense_len}, \field{residual},
\field{status_qualifier}, \field{status}, \field{response} and
\field{sense} fields.
Cheers,
Rusty.
