From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 21 Feb 2023 13:08:12 -0500 From: "Michael S. Tsirkin" Subject: Re: [PATCH v3 1/2] virtio-net: Describe dev cfg fields read only Message-ID: <20230221130713-mutt-send-email-mst@kernel.org> References: <20230217154529.33508-1-parav@nvidia.com> <20230217154529.33508-2-parav@nvidia.com> <87wn4byqqb.fsf@redhat.com> <20230221124013-mutt-send-email-mst@kernel.org> <20230221125057-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=us-ascii Content-Disposition: inline To: Parav Pandit Cc: Cornelia Huck , "virtio-dev@lists.oasis-open.org" , "virtio-comment@lists.oasis-open.org" , Shahaf Shuler List-ID: On Tue, Feb 21, 2023 at 05:59:52PM +0000, Parav Pandit wrote: > > > From: Michael S. Tsirkin > > 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 > > > > 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. > > ? I just concur with Cornelia. > > > 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. writes is plural so "are ignored" but more importantly use rfc terms in normative sections. > > Driver section: > Driver must not write to read-only fields.