From: "Michael S. Tsirkin" <mst@redhat.com>
To: David Edmondson <david.edmondson@oracle.com>
Cc: virtio-comment@lists.oasis-open.org,
virtio-dev@lists.oasis-open.org, jasowang@redhat.com,
cohuck@redhat.com, sgarzare@redhat.com, stefanha@redhat.com,
nrupal.jani@intel.com, Piotr.Uminski@intel.com,
hang.yuan@intel.com, virtio@lists.oasis-open.org,
Zhu Lingshan <lingshan.zhu@intel.com>,
pasic@linux.ibm.com, Shahaf Shuler <shahafs@nvidia.com>,
Parav Pandit <parav@nvidia.com>,
Max Gurtovoy <mgurtovoy@nvidia.com>
Subject: [virtio-dev] Re: [virtio] [PATCH v10 01/10] virtio: document forward compatibility guarantees
Date: Mon, 6 Mar 2023 17:00:16 -0500 [thread overview]
Message-ID: <20230306165907-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <m2leka0yvl.fsf@oracle.com>
On Mon, Mar 06, 2023 at 01:53:50PM +0000, David Edmondson wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
>
> > Feature negotiation forms the basis of forward compatibility
> > guarantees of virtio but has never been properly documented.
> > Do it now.
> >
> > Suggested-by: Halil Pasic <pasic@linux.ibm.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > content.tex | 42 ++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 42 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index 0e474dd..0c2d917 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -114,21 +114,63 @@ \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature B
> > In particular, new fields in the device configuration space are
> > indicated by offering a new feature bit.
> >
> > +To keep the feature negotiation mechanism extensible, it is important
> > +that devices \em{do not} offer any feature bits that they would not be
> > +able to handle if the driver accepted them (even though drivers are not
> > +supposed to accept them in the first place even if offered, according to
> > +this version of the specification.)
>
> I find this (the bit in parenthesis) confusing.
>
> Why are drivers not supposed to accept features that they have been
> offered, given that they can't know that the device cannot handle the
> feature that it just offered?
>
> Is this alluding to the later section:
>
> > feature bits not described in this specification, reserved feature
> > bits and feature bits reserved or not supported for the specific
> > transport or the specific device type
>
> ?
exactly. how would you put this better? given an example?
> > Likewise, it is important that
> > +drivers \em{do not} accept feature bits they do not know how to handle
> > +(even though devices are not supposed to offer them in the first place,
> > +according to this version of the specification.) The preferred way for
> > +handling reserved and unexpected features is that the driver ignores
> > +them.
> > +
> > +In particular, this is
> > +especially important for features limited to specific transports,
> > +as enabling these for more transports in future versions of the
> > +specification is highly likely to require changing the behaviour
> > +from drivers and devices.
>
> "require changed behaviour from drivers and devices".
>
> > Drivers and devices supporting
> > +multiple transports need to carefully maintain per-transport
> > +lists of allowed features.
> > +
> > \drivernormative{\subsection}{Feature Bits}{Basic Facilities of a Virtio Device / Feature Bits}
> > The driver MUST NOT accept a feature which the device did not offer,
> > and MUST NOT accept a feature which requires another feature which was
> > not accepted.
> >
> > +The driver MUST validate the feature bits offered by the device.
> > +The driver MUST ignore and MUST NOT accept any feature bit that is
> > +\begin{itemize}
> > +\item not described in this specification,
> > +\item marked as reserved,
> > +\item not supported for the specific transport,
> > +\item not defined for the device type.
> > +\end{itemize}
> > +
> > The driver SHOULD go into backwards compatibility mode
> > if the device does not offer a feature it understands, otherwise MUST
> > set the FAILED \field{device status} bit and cease initialization.
> >
> > +By contrast, the driver MUST NOT fail solely because a feature
> > +it does not understand has been offered by the device.
> > +
> > \devicenormative{\subsection}{Feature Bits}{Basic Facilities of a Virtio Device / Feature Bits}
> > The device MUST NOT offer a feature which requires another feature
> > which was not offered. The device SHOULD accept any valid subset
> > of features the driver accepts, otherwise it MUST fail to set the
> > FEATURES_OK \field{device status} bit when the driver writes it.
> >
> > +The device MUST NOT offer feature bits corresponding to features
> > +it would not support if accepted by the driver (even if the
> > +driver is prohibited from accepting the feature bits by the
> > +specification); for the sake of clarity, this refers to feature
> > +bits not described in this specification, reserved feature bits
> > +and feature bits reserved or not supported for the specific
> > +transport or the specific device type, but this does not preclude
> > +devices written to a future version of this specification from
> > +offering such feature bits should such a specification have a
> > +provision for devices to support the corresponding features.
> > +
> > If a device has successfully negotiated a set of features
> > at least once (by accepting the FEATURES_OK \field{device
> > status} bit during device initialization), then it SHOULD
> > --
> > MST
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe from this mail list, you must leave the OASIS TC that
> > generates this mail. Follow this link to all your TCs in OASIS at:
> > https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php
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next prev parent reply other threads:[~2023-03-06 22:00 UTC|newest]
Thread overview: 169+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-02 13:04 [virtio-dev] [PATCH v10 00/10] Introduce device group and device management Michael S. Tsirkin
2023-03-02 13:04 ` [virtio-dev] [PATCH v10 01/10] virtio: document forward compatibility guarantees Michael S. Tsirkin
2023-03-02 18:39 ` [virtio-dev] " Parav Pandit
2023-03-02 23:43 ` [virtio-dev] " Michael S. Tsirkin
[not found] ` <m2leka0yvl.fsf@oracle.com>
2023-03-06 22:00 ` Michael S. Tsirkin [this message]
2023-03-07 10:04 ` [virtio-dev] Re: [virtio] " David Edmondson
2023-03-08 14:16 ` Cornelia Huck
2023-03-08 15:04 ` Michael S. Tsirkin
2023-03-02 13:04 ` [virtio-dev] [PATCH v10 02/10] admin: introduce device group and related concepts Michael S. Tsirkin
2023-03-02 18:39 ` [virtio-dev] " Parav Pandit
2023-03-02 23:44 ` [virtio-dev] " Michael S. Tsirkin
2023-03-02 19:40 ` [virtio-dev] Re: [virtio] " Stefan Hajnoczi
2023-03-06 17:00 ` David Edmondson
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 03/10] admin: introduce group administration commands Michael S. Tsirkin
2023-03-02 18:40 ` [virtio-dev] " Parav Pandit
2023-03-02 20:19 ` [virtio-dev] " Stefan Hajnoczi
2023-03-03 0:01 ` Michael S. Tsirkin
2023-03-03 13:17 ` Stefan Hajnoczi
2023-03-03 13:19 ` Michael S. Tsirkin
[not found] ` <4f869944-4ccd-c51e-0f30-dc3ba15ffd52@nvidia.com>
2023-03-07 18:33 ` [virtio-dev] " Parav Pandit
2023-03-08 0:34 ` [virtio-dev] " Michael S. Tsirkin
2023-03-08 1:01 ` [virtio-dev] " Parav Pandit
2023-03-08 1:06 ` [virtio-dev] " Michael S. Tsirkin
2023-03-08 1:14 ` [virtio-dev] " Parav Pandit
[not found] ` <6668fd7a-3eb3-0447-9cbf-72d308b1336a@nvidia.com>
2023-03-08 12:07 ` [virtio-dev] " Michael S. Tsirkin
[not found] ` <992e9a1e-3799-842c-79f3-e66f5c823356@nvidia.com>
2023-03-08 14:43 ` Cornelia Huck
2023-03-08 14:54 ` Michael S. Tsirkin
2023-03-08 15:21 ` Michael S. Tsirkin
[not found] ` <2ef47f53-5978-4b6a-593d-4e94eba0b9ac@nvidia.com>
2023-03-09 6:38 ` [virtio-dev] Re: [virtio-comment] " Michael S. Tsirkin
2023-03-02 23:47 ` [virtio-dev] " Michael S. Tsirkin
2023-03-07 18:26 ` [virtio-dev] " Parav Pandit
2023-03-02 20:10 ` [virtio-dev] " Stefan Hajnoczi
2023-03-02 23:57 ` Michael S. Tsirkin
2023-03-03 13:13 ` Stefan Hajnoczi
2023-03-03 13:18 ` Michael S. Tsirkin
2023-03-03 20:23 ` Stefan Hajnoczi
2023-03-07 11:31 ` Jiri Pirko
2023-03-08 12:03 ` Michael S. Tsirkin
2023-03-07 10:31 ` [virtio-dev] Re: [virtio] " David Edmondson
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 04/10] admin: introduce virtio admin virtqueues Michael S. Tsirkin
2023-03-02 18:40 ` [virtio-dev] " Parav Pandit
2023-03-02 23:48 ` [virtio-dev] " Michael S. Tsirkin
2023-03-02 20:40 ` Stefan Hajnoczi
2023-03-03 0:05 ` Michael S. Tsirkin
2023-03-03 13:28 ` Stefan Hajnoczi
2023-03-03 13:37 ` Michael S. Tsirkin
2023-03-03 20:21 ` [virtio-dev] Re: [virtio] " Stefan Hajnoczi
2023-03-05 9:38 ` Michael S. Tsirkin
2023-03-06 0:03 ` Stefan Hajnoczi
2023-03-06 0:18 ` Michael S. Tsirkin
[not found] ` <20230306110340.GA35392@fedora>
2023-03-06 18:37 ` Michael S. Tsirkin
2023-03-06 20:17 ` Stefan Hajnoczi
2023-03-06 21:43 ` Michael S. Tsirkin
2023-03-31 11:07 ` Michael S. Tsirkin
2023-03-07 8:03 ` [virtio-dev] Re: [virtio-comment] " Jiri Pirko
2023-03-07 14:39 ` Stefan Hajnoczi
2023-03-07 15:07 ` Jiri Pirko
2023-03-07 19:03 ` Stefan Hajnoczi
2023-03-07 19:09 ` [virtio-dev] " Parav Pandit
2023-03-08 5:17 ` [virtio-dev] Re: [virtio] " Jason Wang
2023-03-08 11:58 ` Stefan Hajnoczi
2023-03-08 11:59 ` Michael S. Tsirkin
2023-03-08 10:17 ` [virtio-dev] " Jiri Pirko
2023-03-08 12:44 ` Stefan Hajnoczi
2023-03-08 12:57 ` [virtio-dev] Re: [virtio] " Jiri Pirko
2023-03-08 17:17 ` Stefan Hajnoczi
2023-03-07 16:13 ` [virtio-dev] " Michael S. Tsirkin
2023-03-08 10:08 ` Jiri Pirko
2023-03-08 11:44 ` Michael S. Tsirkin
[not found] ` <7f63fa0a-7deb-5875-6c6b-bfc651681653@redhat.com>
[not found] ` <20230306112030.GB35392@fedora>
[not found] ` <853c78d0-f752-05e9-d79d-811e82801627@nvidia.com>
2023-03-06 16:25 ` [virtio-dev] " Stefan Hajnoczi
2023-03-07 19:04 ` [virtio-dev] " Parav Pandit
[not found] ` <e74483a4-38fa-99b5-86b8-785f0b98d029@nvidia.com>
2023-03-08 14:13 ` [virtio-dev] Re: [virtio-comment] " Stefan Hajnoczi
2023-03-08 16:21 ` [virtio-dev] " Parav Pandit
[not found] ` <18ddbf69-19a6-3c6b-9e42-aaae66e20bcf@nvidia.com>
2023-03-08 17:15 ` [virtio-dev] " Stefan Hajnoczi
2023-03-08 17:21 ` Michael S. Tsirkin
2023-03-09 12:35 ` Stefan Hajnoczi
2023-03-09 13:55 ` Michael S. Tsirkin
2023-03-09 15:56 ` Stefan Hajnoczi
[not found] ` <e8d41902-b794-66e9-8f15-e8617435047c@redhat.com>
2023-03-06 16:22 ` [virtio-dev] " Jiri Pirko
[not found] ` <027fff1b-8ed7-abc0-2331-b188b8822bf4@nvidia.com>
2023-03-06 22:49 ` [virtio-dev] Re: [virtio-comment] " Michael S. Tsirkin
[not found] ` <e12ab469-4586-f0f5-b084-8f2d7c031e11@nvidia.com>
2023-03-08 21:09 ` Michael S. Tsirkin
2023-03-08 21:17 ` [virtio-dev] " Parav Pandit
2023-03-09 7:28 ` [virtio-dev] " Jiri Pirko
2023-03-07 7:56 ` Jiri Pirko
[not found] ` <ZAXfegxCfvfLwiJT@nanopsycho>
2023-03-06 18:40 ` [virtio-dev] Re: [virtio] " Michael S. Tsirkin
2023-03-07 7:36 ` Jiri Pirko
2023-03-07 16:30 ` Michael S. Tsirkin
2023-03-08 10:05 ` [virtio-dev] Re: [virtio-comment] " Jiri Pirko
2023-03-08 11:50 ` Michael S. Tsirkin
2023-03-08 12:08 ` Jiri Pirko
[not found] ` <18d51bc0-d759-1a05-cb7c-3d46c4ed2f1a@nvidia.com>
2023-03-08 18:01 ` David Edmondson
2023-03-08 18:19 ` Jiri Pirko
2023-03-08 21:25 ` [virtio-dev] " Parav Pandit
2023-03-09 7:30 ` [virtio-dev] " Jiri Pirko
2023-03-09 13:04 ` [virtio-dev] " Parav Pandit
2023-03-09 13:57 ` [virtio-dev] " Michael S. Tsirkin
2023-03-09 14:02 ` [virtio-dev] " David Edmondson
2023-03-09 14:11 ` Parav Pandit
2023-03-09 14:22 ` [virtio-dev] " Michael S. Tsirkin
2023-03-09 14:30 ` [virtio-dev] " Parav Pandit
2023-03-09 14:43 ` [virtio-dev] " Michael S. Tsirkin
2023-03-09 16:53 ` [virtio-dev] " Parav Pandit
2023-03-09 17:14 ` [virtio-dev] " Michael S. Tsirkin
2023-03-09 17:16 ` [virtio-dev] " Parav Pandit
2023-03-08 21:45 ` Parav Pandit
2023-03-09 7:37 ` [virtio-dev] " Jiri Pirko
2023-03-09 12:36 ` [virtio-dev] " Parav Pandit
2023-03-09 16:32 ` [virtio-dev] " Jiri Pirko
[not found] ` <17471553-8981-eef9-656b-098e1acdda14@nvidia.com>
2023-03-06 18:44 ` [virtio-dev] " Michael S. Tsirkin
2023-03-07 10:41 ` David Edmondson
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 05/10] pci: add admin vq registers to virtio over pci Michael S. Tsirkin
2023-03-02 20:51 ` [virtio-dev] " Stefan Hajnoczi
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 06/10] mmio: document ADMIN_VQ as reserved Michael S. Tsirkin
2023-03-02 18:40 ` [virtio-dev] " Parav Pandit
2023-03-02 23:51 ` [virtio-dev] " Michael S. Tsirkin
2023-03-02 23:51 ` Michael S. Tsirkin
2023-03-03 8:34 ` Michael S. Tsirkin
[not found] ` <ZAXB44F3MS9CxIiK@nanopsycho>
2023-03-06 18:46 ` [virtio-dev] Re: [virtio] " Michael S. Tsirkin
2023-03-07 7:40 ` [virtio-dev] Re: [virtio-comment] " Jiri Pirko
2023-03-07 18:52 ` [virtio-dev] " Parav Pandit
2023-03-08 16:24 ` [virtio-dev] Re: [virtio-comment] " Cornelia Huck
2023-03-08 16:37 ` [virtio-dev] " Parav Pandit
2023-03-08 16:30 ` [virtio-dev] " Michael S. Tsirkin
2023-03-08 18:21 ` [virtio-dev] Re: [virtio] " Jiri Pirko
2023-03-02 20:52 ` [virtio-dev] " Stefan Hajnoczi
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 07/10] ccw: " Michael S. Tsirkin
2023-03-02 20:53 ` [virtio-dev] " Stefan Hajnoczi
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 08/10] admin: command list discovery Michael S. Tsirkin
2023-03-02 21:09 ` [virtio-dev] " Stefan Hajnoczi
2023-03-31 11:39 ` Michael S. Tsirkin
2023-03-07 10:54 ` [virtio-dev] " David Edmondson
[not found] ` <ZAXbBgN2jw8RhE/3@nanopsycho>
2023-03-08 11:54 ` Michael S. Tsirkin
2023-03-08 12:41 ` Jiri Pirko
2023-03-31 11:43 ` [virtio-dev] Re: [virtio-comment] " Michael S. Tsirkin
2023-03-08 12:38 ` Jiri Pirko
2023-03-10 8:14 ` [virtio-dev] " Zhu, Lingshan
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 09/10] admin: conformance clauses Michael S. Tsirkin
2023-03-07 11:04 ` [virtio-dev] Re: [virtio-comment] " David Edmondson
2023-03-08 11:58 ` Michael S. Tsirkin
2023-03-08 12:59 ` David Edmondson
2023-03-08 13:05 ` [virtio-dev] Re: [virtio] " Jiri Pirko
2023-03-08 13:22 ` Michael S. Tsirkin
2023-03-08 13:44 ` David Edmondson
2023-03-08 14:02 ` Jiri Pirko
2023-03-08 14:12 ` Michael S. Tsirkin
2023-03-10 9:10 ` [virtio-dev] " Zhu, Lingshan
2023-03-10 9:13 ` Michael S. Tsirkin
2023-03-10 18:00 ` Zhu Lingshan
2023-03-10 9:34 ` Michael S. Tsirkin
2023-03-02 13:05 ` [virtio-dev] [PATCH v10 10/10] ccw: document more reserved features Michael S. Tsirkin
2023-03-02 21:12 ` [virtio-dev] " Stefan Hajnoczi
2023-03-02 13:38 ` [virtio-dev] RE: [PATCH v10 00/10] Introduce device group and device management Parav Pandit
2023-03-02 23:27 ` [virtio-dev] " Michael S. Tsirkin
2023-03-02 18:39 ` [virtio-dev] " Parav Pandit
2023-03-06 16:40 ` [virtio-dev] Re: [virtio-comment] " Jiri Pirko
2023-03-06 22:48 ` Michael S. Tsirkin
2023-03-07 7:17 ` Jiri Pirko
2023-03-07 17:15 ` Michael S. Tsirkin
[not found] ` <ZAXcqqdwfoLokT2l@nanopsycho>
2023-03-06 22:54 ` Michael S. Tsirkin
2023-03-07 7:21 ` Jiri Pirko
2023-03-07 17:20 ` Michael S. Tsirkin
2023-03-07 19:31 ` [virtio-dev] " Parav Pandit
2023-03-08 5:11 ` [virtio-dev] " Jason Wang
2023-03-08 12:02 ` [virtio-dev] " Parav Pandit
2023-03-10 8:32 ` [virtio-dev] " Zhu, Lingshan
2023-03-08 9:49 ` [virtio-dev] Re: [virtio] " Jiri Pirko
2023-03-08 16:30 ` [virtio-dev] " Cornelia Huck
2023-03-08 17:22 ` Michael S. Tsirkin
2023-03-08 18:15 ` Jiri Pirko
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