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Subject: RE: [PATCH v3 1/2] virtio-net: Describe dev cfg fields read only
> From: Michael S. Tsirkin <mst@redhat.com> > Sent: Tuesday, February 21, 2023 12:52 PM > > On Tue, Feb 21, 2023 at 05:50:09PM +0000, Parav Pandit wrote: > > > > > > > From: Michael S. Tsirkin <mst@redhat.com> > > > Sent: Tuesday, February 21, 2023 12:42 PM > > > > > > > > What does "bits (for the driver)" mean? It made sense together > > > > with "read-only", but I would drop "(for the driver)" as well. > > > > > > Ouch Parav are you making search and replace changes without reading > > > the result? Pls don't. > > > > > It was wrong to keep the "for the driver". > > I will fix this. > > > > > > > > > > VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. > > > > > > > > > > \begin{lstlisting} > > > > > @@ -167,14 +167,14 @@ \subsection{Device configuration > > > layout}\label{sec:Device Types / Network Device > > > > > #define VIRTIO_NET_S_ANNOUNCE 2 > > > > > \end{lstlisting} > > > > > > > > > > -The following driver-read-only field, > > > > > \field{max_virtqueue_pairs} only exists if > > > > > +The following field, \field{max_virtqueue_pairs} only exists if > > > > > VIRTIO_NET_F_MQ or VIRTIO_NET_F_RSS is set. This field > > > > > specifies the maximum number of each of transmit and receive > > > > > virtqueues (receiveq1\ldots receiveqN and transmitq1\ldots > > > > > transmitqN > > > > > respectively) that can be configured once at least one of these > > > > > features is > > > negotiated. > > > > > > > > > > -The following driver-read-only field, \field{mtu} only exists > > > > > if -VIRTIO_NET_F_MTU is set. This field specifies the maximum > > > > > MTU for the driver to > > > > > +The following field, \field{mtu} only exists if > > > > > +VIRTIO_NET_F_MTU is set. This field specifies the maximum MTU > > > > > +for the driver to > > > > > use. > > > > > > > > > > The following two fields, \field{speed} and \field{duplex}, > > > > > only @@ > > > > > -261,6 +261,8 @@ \subsection{Device configuration > > > > > layout}\label{sec:Device Types / Network Device > > > > > > > > > > \drivernormative{\subsubsection}{Device configuration > > > > > layout}{Device Types / Network Device / Device configuration > > > > > layout} > > > > > > > > > > +All the device configuration fields are read-only for the driver. > > > > > > > > Not sure if this makes a good normative clause, I would rather > > > > give the driver something actionable: > > > > > > > > "A driver SHOULD NOT try to write to any of the device > > > > configuration fields." > > > > > > Agree it's not a normative statement as is. > > > MUST NOT actually - they were always read only. > > > And no need to "try" just don't write period. > > > > > Saying driver must not write it, doesn't make it read only for the device. > > no but this is not what your patch said either. It's read only for the driver. > It is read-only for the driver because the device doesn't treat them as writable. Do you mean it should be better written as, These fields are read-only for the driver, hence any writes by the driver to it will be ignored by the device. ? > > Hence, it should be mentioned as read-only fields, so when the driver writes > something to read-only fields, it can be considered as undefined behavior on > such fields. > > > > In the description not in the normative statements. normative sections just tell > driver what it must and must not do, in the standard RFC terms. > Got it. I will shift them as read-only in the description section. And normative in the device and driver section. Device section: Any writes to config space fields is ignored by the device, because these are read-only fields for the driver. Driver section: Driver must not write to read-only fields.
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