[PATCH] docs: clarify absence of set_features in vhost-user

[PATCH] docs: clarify absence of set_features in vhost-user

[Alyssa Ross]

The previous wording was (at least to me) ambiguous about whether a
backend should enable features immediately after they were set using
VHOST_USER_SET_PROTOCOL_FEATURES, or wait for support for protocol
features to be acknowledged if it hasn't been yet before enabling
those features.

This patch attempts to make it clearer that
VHOST_USER_SET_PROTOCOL_FEATURES should immediately enable features,
even if support for protocol features has not yet been acknowledged,
while still also making clear that the frontend SHOULD acknowledge
support for protocol features.

Previous discussion begins here:
<https://lore.kernel.org/qemu-devel/87sgd1ktx9.fsf@alyssa.is/>

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Alyssa Ross <hi@alyssa.is>
---
 docs/interop/vhost-user.rst | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 10e3e3475e..bc78c9947f 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -854,9 +854,9 @@ Master message types
   ``VHOST_USER_GET_FEATURES``.
 
 .. Note::
-   Slave that reported ``VHOST_USER_F_PROTOCOL_FEATURES`` must
-   support this message even before ``VHOST_USER_SET_FEATURES`` was
-   called.
+   While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
+   backend must allow ``VHOST_USER_GET_PROTOCOL_FEATURES`` even if
+   ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.
 
 ``VHOST_USER_SET_PROTOCOL_FEATURES``
   :id: 16
@@ -869,8 +869,12 @@ Master message types
   ``VHOST_USER_GET_FEATURES``.
 
 .. Note::
-   Slave that reported ``VHOST_USER_F_PROTOCOL_FEATURES`` must support
-   this message even before ``VHOST_USER_SET_FEATURES`` was called.
+   While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
+   backend must allow ``VHOST_USER_SET_PROTOCOL_FEATURES`` even if
+   ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.
+   The backend must not wait for ``VHOST_USER_SET_FEATURES`` before
+   enabling protocol features requested with
+   ``VHOST_USER_SET_PROTOCOL_FEATURES``.
 
 ``VHOST_USER_SET_OWNER``
   :id: 3
-- 
2.27.0

Re: [PATCH] docs: clarify absence of set_features in vhost-user

[no-reply]

Patchew URL: https://patchew.org/QEMU/20200813094847.4288-1-hi@alyssa.is/



Hi,

This series failed the docker-quick@centos7 build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
make docker-image-centos7 V=1 NETWORK=1
time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1
=== TEST SCRIPT END ===

  TEST    check-unit: tests/test-char
Unexpected error in object_property_try_add() at /tmp/qemu-test/src/qom/object.c:1181:
attempt to add duplicate property 'serial-id' to object (type 'container')
ERROR test-char - too few tests run (expected 38, got 9)
make: *** [check-unit] Error 1
make: *** Waiting for unfinished jobs....
  TEST    iotest-qcow2: 029
  TEST    check-qtest-x86_64: tests/qtest/hd-geo-test
---
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=1abfbcb84f8f42b78a78bf6a1f43f577', '-u', '1003', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=1', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew2/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-h1scwc1j/src/docker-src.2020-08-13-12.14.52.15688:/var/tmp/qemu:z,ro', 'qemu/centos7', '/var/tmp/qemu/run', 'test-quick']' returned non-zero exit status 2.
filter=--filter=label=com.qemu.instance.uuid=1abfbcb84f8f42b78a78bf6a1f43f577
make[1]: *** [docker-run] Error 1
make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-h1scwc1j/src'
make: *** [docker-run-test-quick@centos7] Error 2

real    13m11.179s
user    0m8.107s


The full log is available at
http://patchew.org/logs/20200813094847.4288-1-hi@alyssa.is/testing.docker-quick@centos7/?type=message.
---
Email generated automatically by Patchew [https://patchew.org/].
Please send your feedback to patchew-devel@redhat.com

Re: [PATCH] docs: clarify absence of set_features in vhost-user

[Alex Bennée]

Alyssa Ross <hi@alyssa.is> writes:

> The previous wording was (at least to me) ambiguous about whether a
> backend should enable features immediately after they were set using
> VHOST_USER_SET_PROTOCOL_FEATURES, or wait for support for protocol
> features to be acknowledged if it hasn't been yet before enabling
> those features.
>
> This patch attempts to make it clearer that
> VHOST_USER_SET_PROTOCOL_FEATURES should immediately enable features,
> even if support for protocol features has not yet been acknowledged,
> while still also making clear that the frontend SHOULD acknowledge
> support for protocol features.
>
> Previous discussion begins here:
> <https://lore.kernel.org/qemu-devel/87sgd1ktx9.fsf@alyssa.is/>
>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
>  docs/interop/vhost-user.rst | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> index 3f18ab424e..c8b9771a16 100644
> --- a/docs/interop/vhost-user.rst
> +++ b/docs/interop/vhost-user.rst
> @@ -906,9 +906,9 @@ Front-end message types
>    ``VHOST_USER_SET_FEATURES``.
>  
>  .. Note::
> -   Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must
> -   support this message even before ``VHOST_USER_SET_FEATURES`` was
> -   called.
> +   While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
> +   back-end must allow ``VHOST_USER_GET_PROTOCOL_FEATURES`` even if
> +   ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.

I think this is just restating the same logic from above introduced in:

  fa9972662c (vhost-user.rst: add clarifying language about protocol negotiation)

that we don't need VHOST_USER_F_PROTOCOL_FEATURES to be acked by
VHOST_USER_SET_FEATURES? I agree the wording is hard to follow though. I
suspect what would really help is some clear message sequence diagrams
in the document showing the negotiation steps.


>  
>  ``VHOST_USER_SET_PROTOCOL_FEATURES``
>    :id: 16
> @@ -923,8 +923,12 @@ Front-end message types
>    ``VHOST_USER_SET_FEATURES``.
>  
>  .. Note::
> -   Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must support
> -   this message even before ``VHOST_USER_SET_FEATURES`` was called.
> +   While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
> +   back-end must allow ``VHOST_USER_SET_PROTOCOL_FEATURES`` even if
> +   ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.
> +   The back-end must not wait for ``VHOST_USER_SET_FEATURES`` before
> +   enabling protocol features requested with
> +   ``VHOST_USER_SET_PROTOCOL_FEATURES``.
>  
>  ``VHOST_USER_SET_OWNER``
>    :id: 3
>
> base-commit: e93ded1bf6c94ab95015b33e188bc8b0b0c32670


-- 
Alex Bennée

[PATCH] docs: clarify absence of set_features in vhost-user

[Alyssa Ross]

The previous wording was (at least to me) ambiguous about whether a
backend should enable features immediately after they were set using
VHOST_USER_SET_PROTOCOL_FEATURES, or wait for support for protocol
features to be acknowledged if it hasn't been yet before enabling
those features.

This patch attempts to make it clearer that
VHOST_USER_SET_PROTOCOL_FEATURES should immediately enable features,
even if support for protocol features has not yet been acknowledged,
while still also making clear that the frontend SHOULD acknowledge
support for protocol features.

Previous discussion begins here:
<https://lore.kernel.org/qemu-devel/87sgd1ktx9.fsf@alyssa.is/>

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Alyssa Ross <hi@alyssa.is>
---
 docs/interop/vhost-user.rst | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 3f18ab424e..c8b9771a16 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -906,9 +906,9 @@ Front-end message types
   ``VHOST_USER_SET_FEATURES``.
 
 .. Note::
-   Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must
-   support this message even before ``VHOST_USER_SET_FEATURES`` was
-   called.
+   While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
+   back-end must allow ``VHOST_USER_GET_PROTOCOL_FEATURES`` even if
+   ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.
 
 ``VHOST_USER_SET_PROTOCOL_FEATURES``
   :id: 16
@@ -923,8 +923,12 @@ Front-end message types
   ``VHOST_USER_SET_FEATURES``.
 
 .. Note::
-   Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must support
-   this message even before ``VHOST_USER_SET_FEATURES`` was called.
+   While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
+   back-end must allow ``VHOST_USER_SET_PROTOCOL_FEATURES`` even if
+   ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.
+   The back-end must not wait for ``VHOST_USER_SET_FEATURES`` before
+   enabling protocol features requested with
+   ``VHOST_USER_SET_PROTOCOL_FEATURES``.
 
 ``VHOST_USER_SET_OWNER``
   :id: 3

base-commit: e93ded1bf6c94ab95015b33e188bc8b0b0c32670
-- 
2.37.1