From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 5 Oct 2023 13:43:33 -0400 From: Stefan Hajnoczi Message-ID: <20231005174333.GD1342722@fedora> References: <20231004125904.110781-1-hreitz@redhat.com> <20231004125904.110781-4-hreitz@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="t+JYja1hNqvjfZWk" Content-Disposition: inline In-Reply-To: <20231004125904.110781-4-hreitz@redhat.com> Subject: Re: [Virtio-fs] [PATCH v4 3/8] vhost-user.rst: Clarify enabling/disabling vrings List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Hanna Czenczek Cc: qemu-devel@nongnu.org, virtio-fs@redhat.com, "Michael S . Tsirkin" , German Maglione , Eugenio =?iso-8859-1?Q?P=E9rez?= , Anton Kuchin --t+JYja1hNqvjfZWk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Oct 04, 2023 at 02:58:59PM +0200, Hanna Czenczek wrote: > Currently, the vhost-user documentation says that rings are to be > initialized in a disabled state when VHOST_USER_F_PROTOCOL_FEATURES is > negotiated. However, by the time of feature negotiation, all rings have > already been initialized, so it is not entirely clear what this means. >=20 > At least the vhost-user-backend Rust crate's implementation interpreted > it to mean that whenever this feature is negotiated, all rings are to > put into a disabled state, which means that every SET_FEATURES call > would disable all rings, effectively halting the device. This is > problematic because the VHOST_F_LOG_ALL feature is also set or cleared > this way, which happens during migration. Doing so should not halt the > device. >=20 > Other implementations have interpreted this to mean that the device is > to be initialized with all rings disabled, and a subsequent SET_FEATURES > call that does not set VHOST_USER_F_PROTOCOL_FEATURES will enable all of > them. Here, SET_FEATURES will never disable any ring. >=20 > This interpretation does not suffer the problem of unintentionally > halting the device whenever features are set or cleared, so it seems > better and more reasonable. >=20 > We can clarify this in the documentation by making it explicit that the > enabled/disabled state is tracked even while the vring is stopped. > Every vring is initialized in a disabled state, and SET_FEATURES without > VHOST_USER_F_PROTOCOL_FEATURES simply becomes one way to enable all > vrings. >=20 > Signed-off-by: Hanna Czenczek > --- > docs/interop/vhost-user.rst | 32 +++++++++++++++++--------------- > 1 file changed, 17 insertions(+), 15 deletions(-) Reviewed-by: Stefan Hajnoczi --t+JYja1hNqvjfZWk Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmUe9cUACgkQnKSrs4Gr c8hqeQf+J8jHFezwIR2ygsUKJwEjYNdeoaFotnS5EMqR8I+Hw2lPWz6qeWKBKCxt 97zucS5Cuae/QH8sMKlb+c9FvGAG+3ibNFTQNo0U51s7eZzUQVLTjRYFLY+q7e1Q fcXqP0ju7ZoXvEYsjuaLqXMyfPNWLMesoOpE9nmPErW7QtZXMd5utSFphqUNIp3O GQGKynO33pfkolMqLBBa9tcYV6bSfKV/jlJMmMz2AZIYvmfj1uajomU08JLuVznt Lpx/fZj8QLkyKeTK63Xr0YcyV/XnSRlW/UuJIluis0Uagc42G03wNVmD32TAL5NE 30sSwJAK+GI5q+Ae8UI4msWvN0BuMQ== =8Kbw -----END PGP SIGNATURE----- --t+JYja1hNqvjfZWk--