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Fri, 01 Sep 2023 05:00:01 -0700 (PDT) MIME-Version: 1.0 References: <20230901110018.3704459-1-alex.bennee@linaro.org> In-Reply-To: <20230901110018.3704459-1-alex.bennee@linaro.org> From: Albert Esteve Date: Fri, 1 Sep 2023 13:59:49 +0200 Message-ID: Subject: Re: [virtio-dev] [RFC PATCH v2] docs/interop: define PROBE feature for vhost-user VirtIO devices To: =?UTF-8?B?QWxleCBCZW5uw6ll?= Cc: slp@redhat.com, mst@redhat.com, marcandre.lureau@redhat.com, stefanha@redhat.com, viresh.kumar@linaro.org, sgarzare@redhat.com, takahiro.akashi@linaro.org, erik.schilling@linaro.org, manos.pitsidianakis@linaro.org, mathieu.poirier@linaro.org, qemu-devel@nongnu.org, virtio-dev@lists.oasis-open.org, virtio-comment@lists.oasis-open.org Content-Type: multipart/alternative; boundary="0000000000007a5f3506044ae6eb" Received-SPF: pass client-ip=170.10.129.124; envelope-from=aesteve@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --0000000000007a5f3506044ae6eb Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable This looks great! Thanks for this proposal. On Fri, Sep 1, 2023 at 1:00=E2=80=AFPM Alex Benn=C3=A9e wrote: > Currently QEMU has to know some details about the VirtIO device > supported by a vhost-user daemon to be able to setup the guest. This > makes it hard for QEMU to add support for additional vhost-user > daemons without adding specific stubs for each additional VirtIO > device. > > This patch suggests a new feature flag (VHOST_USER_PROTOCOL_F_PROBE) > which the back-end can advertise which allows a probe message to be > sent to get all the details QEMU needs to know in one message. > > Together with the existing features VHOST_USER_PROTOCOL_F_STATUS and > VHOST_USER_PROTOCOL_F_CONFIG we can create "standalone" vhost-user > daemons which are capable of handling all aspects of the VirtIO > transactions with only a generic stub on the QEMU side. These daemons > can also be used without QEMU in situations where there isn't a full > VMM managing their setup. > > Signed-off-by: Alex Benn=C3=A9e > > --- > v2 > - dropped F_STANDALONE in favour of F_PROBE > - split probe details across several messages > - probe messages don't automatically imply a standalone daemon > - add wording where probe details interact (F_MQ/F_CONFIG) > - define VMM and make clear QEMU is only one of many potential VMMs > - reword commit message > --- > docs/interop/vhost-user.rst | 90 ++++++++++++++++++++++++++++++++----- > hw/virtio/vhost-user.c | 8 ++++ > 2 files changed, 88 insertions(+), 10 deletions(-) > > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > index 5a070adbc1..ba3b5e07b7 100644 > --- a/docs/interop/vhost-user.rst > +++ b/docs/interop/vhost-user.rst > @@ -7,6 +7,7 @@ Vhost-user Protocol > .. > Copyright 2014 Virtual Open Systems Sarl. > Copyright 2019 Intel Corporation > + Copyright 2023 Linaro Ltd > Licence: This work is licensed under the terms of the GNU GPL, > version 2 or later. See the COPYING file in the top-level > directory. > @@ -27,17 +28,31 @@ The protocol defines 2 sides of the communication, > *front-end* and > *back-end*. The *front-end* is the application that shares its > virtqueues, in > our case QEMU. The *back-end* is the consumer of the virtqueues. > > -In the current implementation QEMU is the *front-end*, and the *back-end= * > -is the external process consuming the virtio queues, for example a > -software Ethernet switch running in user space, such as Snabbswitch, > -or a block device back-end processing read & write to a virtual > -disk. In order to facilitate interoperability between various back-end > -implementations, it is recommended to follow the :ref:`Backend program > -conventions `. > +In the current implementation a Virtual Machine Manager (VMM) such as > +QEMU is the *front-end*, and the *back-end* is the external process > +consuming the virtio queues, for example a software Ethernet switch > +running in user space, such as Snabbswitch, or a block device back-end > +processing read & write to a virtual disk. In order to facilitate > +interoperability between various back-end implementations, it is > +recommended to follow the :ref:`Backend program conventions > +`. > > The *front-end* and *back-end* can be either a client (i.e. connecting) = or > server (listening) in the socket communication. > > +Probing device details > +---------------------- > + > +Traditionally the vhost-user daemon *back-end* shares configuration > +responsibilities with the VMM *front-end* which needs to know certain > +key bits of information about the device. This means the VMM needs to > +define at least a minimal stub for each VirtIO device it wants to > +support. If the daemon supports the right set of protocol features the > +VMM can probe the daemon for the information it needs to setup the > +device. See :ref:`Probing features for standalone daemons > +` for more details. > + > + > Support for platforms other than Linux > -------------------------------------- > > @@ -316,6 +331,7 @@ replies. Here is a list of the ones that do: > * ``VHOST_USER_GET_VRING_BASE`` > * ``VHOST_USER_SET_LOG_BASE`` (if ``VHOST_USER_PROTOCOL_F_LOG_SHMFD``) > * ``VHOST_USER_GET_INFLIGHT_FD`` (if > ``VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD``) > +* ``VHOST_USER_GET_BACKEND_SPECS`` (if > ``VHOST_USER_PROTOCOL_F_STANDALONE``) > > .. seealso:: > > @@ -396,9 +412,10 @@ must support changing some configuration aspects on > the fly. > Multiple queue support > ---------------------- > > -Many devices have a fixed number of virtqueues. In this case the > front-end > -already knows the number of available virtqueues without communicating > with the > -back-end. > +Many devices have a fixed number of virtqueues. In this case the > +*front-end* usually already knows the number of available virtqueues > +without communicating with the back-end. For standalone daemons this > +number can be can be probed with the ``VHOST_USER_GET_MIN_VQ`` message. > > Some devices do not have a fixed number of virtqueues. Instead the > maximum > number of virtqueues is chosen by the back-end. The number can depend o= n > host > @@ -885,6 +902,23 @@ Protocol features > #define VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS 15 > #define VHOST_USER_PROTOCOL_F_STATUS 16 > #define VHOST_USER_PROTOCOL_F_XEN_MMAP 17 > + #define VHOST_USER_PROTOCOL_F_PROBE 18 > + > +.. _probing_features: > + > +Probing features for standalone daemons > +--------------------------------------- > + > +The protocol feature ``VHOST_USER_PROTOCOL_F_PROBE`` enables a number > +of additional messages which allow the *front-end* to probe details > +about the VirtIO device from the *back-end*. However for a *back-end* > +to be described as standalone it must also support: > + > + * ``VHOST_USER_PROTOCOL_F_STATUS`` > + * ``VHOST_USER_PROTOCOL_F_CONFIG`` (if there is a config space) > + > +which are required to ensure the *back-end* daemon can operate > +without the *front-end* managing some aspects of its configuration. > > Front-end message types > ----------------------- > @@ -1440,6 +1474,42 @@ Front-end message types > query the back-end for its device status as defined in the Virtio > specification. > > +``VHOST_USER_GET_DEVICE_ID`` > + :id: 41 > + :request payload: N/A > + :reply payload: ``u32`` > + > + When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has been > + successfully negotiated, this message is submitted by the front-end > + to query what VirtIO device the back-end support. This is intended > + to remove the need for the front-end to know ahead of time what the > + VirtIO device the backend emulates is. > + > +``VHOST_USER_GET_CONFIG_SIZE`` > + :id: 42 > + :request payload: N/A > + :reply payload: ``u32`` > + > + When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has been > + successfully negotiated, this message is submitted by the front-end > + to query the size of the VirtIO device's config space. This is > + intended to remove the need for the front-end to know ahead of time > + what the size is. Replying with 0 when > + ``VHOST_USER_PROTOCOL_F_CONFIG`` has been negotiated would indicate > + an bug. > + > +``VHOST_USER_GET_MIN_VQ`` > + :id: 43 > + :request payload: N/A > + :reply payload: ``u32`` > + > + When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has been > + successfully negotiated, this message is submitted by the front-end to > + query minimum number of VQ's required to support the device. A > + device may support more than this number of VQ's if it advertises > + the ``VHOST_USER_PROTOCOL_F_MQ`` protocol feature. Reporting a > + number greater than the result of ``VHOST_USER_GET_QUEUE_NUM`` would > + indicate a bug. > > Maybe I lack some background, but not sure what min_vq is here? This looks like quering the number of VQs the backend requires/uses. Which, in case of MQ, it may be bigger (which is where I assume comes the `min` part, if we consider `VHOST_USER_GET_QUEUE_NUM` the `max`). Couldn't we reuse the `VHOST_USER_GET_QUEUE_NUM` type for this? > Back-end message types > ---------------------- > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c > index 8dcf049d42..4d433cdf2b 100644 > --- a/hw/virtio/vhost-user.c > +++ b/hw/virtio/vhost-user.c > @@ -202,6 +202,13 @@ typedef struct VhostUserInflight { > uint16_t queue_size; > } VhostUserInflight; > > +typedef struct VhostUserBackendSpecs { > + uint32_t device_id; > + uint32_t config_size; > + uint32_t min_vqs; > + uint32_t max_vqs; > +} VhostUserBackendSpecs; > + > typedef struct { > VhostUserRequest request; > > @@ -226,6 +233,7 @@ typedef union { > VhostUserCryptoSession session; > VhostUserVringArea area; > VhostUserInflight inflight; > + VhostUserBackendSpecs specs; > } VhostUserPayload; > > typedef struct VhostUserMsg { > -- > 2.39.2 > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org > > --0000000000007a5f3506044ae6eb Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
This looks great! Thanks for this proposal.

On= Fri, Sep 1, 2023 at 1:00=E2=80=AFPM Alex Benn=C3=A9e <alex.bennee@linaro.org> wrote:
Currently QEMU has to know s= ome details about the VirtIO device
supported by a vhost-user daemon to be able to setup the guest. This
makes it hard for QEMU to add support for additional vhost-user
daemons without adding specific stubs for each additional VirtIO
device.

This patch suggests a new feature flag (VHOST_USER_PROTOCOL_F_PROBE)
which the back-end can advertise which allows a probe message to be
sent to get all the details QEMU needs to know in one message.

Together with the existing features VHOST_USER_PROTOCOL_F_STATUS and
VHOST_USER_PROTOCOL_F_CONFIG we can create "standalone" vhost-use= r
daemons which are capable of handling all aspects of the VirtIO
transactions with only a generic stub on the QEMU side. These daemons
can also be used without QEMU in situations where there isn't a full VMM managing their setup.

Signed-off-by: Alex Benn=C3=A9e <alex.bennee@linaro.org>

---
v2
=C2=A0 - dropped F_STANDALONE in favour of F_PROBE
=C2=A0 - split probe details across several messages
=C2=A0 - probe messages don't automatically imply a standalone daemon =C2=A0 - add wording where probe details interact (F_MQ/F_CONFIG)
=C2=A0 - define VMM and make clear QEMU is only one of many potential VMMs<= br> =C2=A0 - reword commit message
---
=C2=A0docs/interop/vhost-user.rst | 90 ++++++++++++++++++++++++++++++++----= -
=C2=A0hw/virtio/vhost-user.c=C2=A0 =C2=A0 =C2=A0 |=C2=A0 8 ++++
=C2=A02 files changed, 88 insertions(+), 10 deletions(-)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 5a070adbc1..ba3b5e07b7 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -7,6 +7,7 @@ Vhost-user Protocol
=C2=A0..
=C2=A0 =C2=A0Copyright 2014 Virtual Open Systems Sarl.
=C2=A0 =C2=A0Copyright 2019 Intel Corporation
+=C2=A0 Copyright 2023 Linaro Ltd
=C2=A0 =C2=A0Licence: This work is licensed under the terms of the GNU GPL,=
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 version 2 or later. See the COPYI= NG file in the top-level
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 directory.
@@ -27,17 +28,31 @@ The protocol defines 2 sides of the communication, *fro= nt-end* and
=C2=A0*back-end*. The *front-end* is the application that shares its virtqu= eues, in
=C2=A0our case QEMU. The *back-end* is the consumer of the virtqueues.

-In the current implementation QEMU is the *front-end*, and the *back-end*<= br> -is the external process consuming the virtio queues, for example a
-software Ethernet switch running in user space, such as Snabbswitch,
-or a block device back-end processing read & write to a virtual
-disk. In order to facilitate interoperability between various back-end
-implementations, it is recommended to follow the :ref:`Backend program
-conventions <backend_conventions>`.
+In the current implementation a Virtual Machine Manager (VMM) such as
+QEMU is the *front-end*, and the *back-end* is the external process
+consuming the virtio queues, for example a software Ethernet switch
+running in user space, such as Snabbswitch, or a block device back-end
+processing read & write to a virtual disk. In order to facilitate
+interoperability between various back-end implementations, it is
+recommended to follow the :ref:`Backend program conventions
+<backend_conventions>`.

=C2=A0The *front-end* and *back-end* can be either a client (i.e. connectin= g) or
=C2=A0server (listening) in the socket communication.

+Probing device details
+----------------------
+
+Traditionally the vhost-user daemon *back-end* shares configuration
+responsibilities with the VMM *front-end* which needs to know certain
+key bits of information about the device. This means the VMM needs to
+define at least a minimal stub for each VirtIO device it wants to
+support. If the daemon supports the right set of protocol features the
+VMM can probe the daemon for the information it needs to setup the
+device. See :ref:`Probing features for standalone daemons
+<probing_features>` for more details.
+
+
=C2=A0Support for platforms other than Linux
=C2=A0--------------------------------------

@@ -316,6 +331,7 @@ replies. Here is a list of the ones that do:
=C2=A0* ``VHOST_USER_GET_VRING_BASE``
=C2=A0* ``VHOST_USER_SET_LOG_BASE`` (if ``VHOST_USER_PROTOCOL_F_LOG_SHMFD``= )
=C2=A0* ``VHOST_USER_GET_INFLIGHT_FD`` (if ``VHOST_USER_PROTOCOL_F_INFLIGHT= _SHMFD``)
+* ``VHOST_USER_GET_BACKEND_SPECS`` (if ``VHOST_USER_PROTOCOL_F_STANDALONE`= `)

=C2=A0.. seealso::

@@ -396,9 +412,10 @@ must support changing some configuration aspects on th= e fly.
=C2=A0Multiple queue support
=C2=A0----------------------

-Many devices have a fixed number of virtqueues.=C2=A0 In this case the fro= nt-end
-already knows the number of available virtqueues without communicating wit= h the
-back-end.
+Many devices have a fixed number of virtqueues. In this case the
+*front-end* usually already knows the number of available virtqueues
+without communicating with the back-end. For standalone daemons this
+number can be can be probed with the ``VHOST_USER_GET_MIN_VQ`` message.
=C2=A0Some devices do not have a fixed number of virtqueues.=C2=A0 Instead = the maximum
=C2=A0number of virtqueues is chosen by the back-end.=C2=A0 The number can = depend on host
@@ -885,6 +902,23 @@ Protocol features
=C2=A0 =C2=A0#define VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS=C2=A0 15
=C2=A0 =C2=A0#define VHOST_USER_PROTOCOL_F_STATUS=C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A016
=C2=A0 =C2=A0#define VHOST_USER_PROTOCOL_F_XEN_MMAP=C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A017
+=C2=A0 #define VHOST_USER_PROTOCOL_F_PROBE=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 18
+
+.. _probing_features:
+
+Probing features for standalone daemons
+---------------------------------------
+
+The protocol feature ``VHOST_USER_PROTOCOL_F_PROBE`` enables a number
+of additional messages which allow the *front-end* to probe details
+about the VirtIO device from the *back-end*. However for a *back-end*
+to be described as standalone it must also support:
+
+=C2=A0 * ``VHOST_USER_PROTOCOL_F_STATUS``
+=C2=A0 * ``VHOST_USER_PROTOCOL_F_CONFIG`` (if there is a config space)
+
+which are required to ensure the *back-end* daemon can operate
+without the *front-end* managing some aspects of its configuration.

=C2=A0Front-end message types
=C2=A0-----------------------
@@ -1440,6 +1474,42 @@ Front-end message types
=C2=A0 =C2=A0query the back-end for its device status as defined in the Vir= tio
=C2=A0 =C2=A0specification.

+``VHOST_USER_GET_DEVICE_ID``
+=C2=A0 :id: 41
+=C2=A0 :request payload: N/A
+=C2=A0 :reply payload: ``u32``
+
+=C2=A0 When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has been<= br> +=C2=A0 successfully negotiated, this message is submitted by the front-end=
+=C2=A0 to query what VirtIO device the back-end support. This is intended<= br> +=C2=A0 to remove the need for the front-end to know ahead of time what the=
+=C2=A0 VirtIO device the backend emulates is.
+
+``VHOST_USER_GET_CONFIG_SIZE``
+=C2=A0 :id: 42
+=C2=A0 :request payload: N/A
+=C2=A0 :reply payload: ``u32``
+
+=C2=A0 When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has been<= br> +=C2=A0 successfully negotiated, this message is submitted by the front-end=
+=C2=A0 to query the size of the VirtIO device's config space. This is<= br> +=C2=A0 intended to remove the need for the front-end to know ahead of time=
+=C2=A0 what the size is. Replying with 0 when
+=C2=A0 ``VHOST_USER_PROTOCOL_F_CONFIG`` has been negotiated would indicate=
+=C2=A0 an bug.
+
+``VHOST_USER_GET_MIN_VQ``
+=C2=A0 :id: 43
+=C2=A0 :request payload: N/A
+=C2=A0 :reply payload: ``u32``
+
+=C2=A0 When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has been<= br> +=C2=A0 successfully negotiated, this message is submitted by the front-end= to
+=C2=A0 query minimum number of VQ's required to support the device. A<= br> +=C2=A0 device may support more than this number of VQ's if it advertis= es
+=C2=A0 the ``VHOST_USER_PROTOCOL_F_MQ`` protocol feature. Reporting a
+=C2=A0 number greater than the result of ``VHOST_USER_GET_QUEUE_NUM`` woul= d
+=C2=A0 indicate a bug.


Maybe I lack some background, but not = sure what min_vq is here?
This looks like quering=C2=A0the number= of VQs the backend requires/uses.
Which, in case of MQ, it may b= e bigger (which is where I assume comes the `min`
part, if we con= sider `VHOST_USER_GET_QUEUE_NUM` the `max`).

Could= n't we reuse the `VHOST_USER_GET_QUEUE_NUM` type for this?
= =C2=A0
=C2=A0Back-end message types
=C2=A0----------------------
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 8dcf049d42..4d433cdf2b 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -202,6 +202,13 @@ typedef struct VhostUserInflight {
=C2=A0 =C2=A0 =C2=A0uint16_t queue_size;
=C2=A0} VhostUserInflight;

+typedef struct VhostUserBackendSpecs {
+=C2=A0 =C2=A0 uint32_t device_id;
+=C2=A0 =C2=A0 uint32_t config_size;
+=C2=A0 =C2=A0 uint32_t min_vqs;
+=C2=A0 =C2=A0 uint32_t max_vqs;
+} VhostUserBackendSpecs;
+
=C2=A0typedef struct {
=C2=A0 =C2=A0 =C2=A0VhostUserRequest request;

@@ -226,6 +233,7 @@ typedef union {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0VhostUserCryptoSession session;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0VhostUserVringArea area;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0VhostUserInflight inflight;
+=C2=A0 =C2=A0 =C2=A0 =C2=A0 VhostUserBackendSpecs specs;
=C2=A0} VhostUserPayload;

=C2=A0typedef struct VhostUserMsg {
--
2.39.2


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