From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 5 Oct 2023 13:48:11 -0400 From: Stefan Hajnoczi Message-ID: <20231005174811.GJ1342722@fedora> References: <20231004125904.110781-1-hreitz@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="mNw8fgYOgCi8R7Nz" Content-Disposition: inline In-Reply-To: <20231004125904.110781-1-hreitz@redhat.com> Subject: Re: [Virtio-fs] [PATCH v4 0/8] vhost-user: Back-end state migration 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 --mNw8fgYOgCi8R7Nz Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Oct 04, 2023 at 02:58:56PM +0200, Hanna Czenczek wrote: > RFC: > https://lists.nongnu.org/archive/html/qemu-devel/2023-03/msg04263.html >=20 > v1: > https://lists.nongnu.org/archive/html/qemu-devel/2023-04/msg01575.html >=20 > v2: > https://lists.nongnu.org/archive/html/qemu-devel/2023-07/msg02604.html >=20 > v3: > https://lists.nongnu.org/archive/html/qemu-devel/2023-09/msg03750.html >=20 >=20 > Based-on: <20231004014532.1228637-1-stefanha@redhat.com> > ([PATCH v2 0/3] vhost: clean up device reset) >=20 >=20 > Hi, >=20 > This v4 includes largely unchanged patches from v3. The main > addition/change is what came out of the discussion between Stefan and me > around how to proceed without SUSPEND/RESUME, which is that this series > is now based on his reset fix, and it includes more documentation > changes. This looks good. I posted some minor comments on the new patches. Stefan >=20 > Changes in detail: >=20 > - Patch 1: Fall-out from the reset fix: Currently, the status byte is > effectively unused (qemu only uses it for resetting, which all > back-ends ignore; DPDK uses it to announce potential feature > negotiation failure, which qemu ignores). It is also not defined what > exactly front-end or back-end should do with this byte, except > pointing at the virtio spec, which however naturally does not say how > this integrates with vhost-user=E2=80=99s RESET_DEVICE or [GS]ET_FEATUR= ES. > Furthermore, there does not seem to be a use for this; we have > RESET_DEVICE for resetting, and we have [GS]ET_FEATURES (and > REPLY_ACK, which can be used on SET_FEATURES) for feature > negotation. > Therefore, deprecate the status byte, pointing to those other commands > instead. >=20 > - Patch 2: Patch 4 defines a suspended state for the whole back-end if > all vrings are stopped. I think this should be mentioned in > GET_VRING_BASE, but upon trying to add it, I found that it does not > even mention that it stops the vring (mentioned only in the Ring > States section), and remembered that the whole description of both > GET_VRING_BASE and SET_VRING_BASE really was not helpful when trying > to implement a vhost-user back-end. Took the opportunity to overhaul > both. >=20 > - Patch 3: This one=E2=80=99s from v3, but quite heavily modified. Stefan > suggested consistently defining the started/stopped and > enabled/disabled states to be independent, and indeed doing so > simplifies a whole lot of stuff. Specifically, it makes the magic > =E2=80=9Cenabled/disabled when started=E2=80=9D go away. Basically, I = found this > change alone is enough to remove the confusion I had with the existing > documentation. >=20 > - Patch 4: As suggested by Stefan, just define a suspended state without > introducing SUSPEND. vDPA needs SUSPEND because its GET_VRING_BASE > does not stop the vring, but vhost-user=E2=80=99s does, so we can defin= e the > suspended state to be when all vrings are stopped. >=20 > - Patch 5: Reference the suspended state. >=20 > - Patches 6 through 8: Unmodified, except for them being rebase on > Stefan=E2=80=99s series. >=20 >=20 > Hanna Czenczek (8): > vhost-user.rst: Deprecate [GS]ET_STATUS > vhost-user.rst: Improve [GS]ET_VRING_BASE doc > vhost-user.rst: Clarify enabling/disabling vrings > vhost-user.rst: Introduce suspended state > vhost-user.rst: Migrating back-end-internal state > vhost-user: Interface for migration state transfer > vhost: Add high-level state save/load functions > vhost-user-fs: Implement internal migration >=20 > docs/interop/vhost-user.rst | 318 +++++++++++++++++++++++++++--- > include/hw/virtio/vhost-backend.h | 24 +++ > include/hw/virtio/vhost.h | 113 +++++++++++ > hw/virtio/vhost-user-fs.c | 101 +++++++++- > hw/virtio/vhost-user.c | 148 ++++++++++++++ > hw/virtio/vhost.c | 241 ++++++++++++++++++++++ > 6 files changed, 917 insertions(+), 28 deletions(-) >=20 > --=20 > 2.41.0 >=20 --mNw8fgYOgCi8R7Nz Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmUe9tsACgkQnKSrs4Gr c8iA0QgAgmWhPPx/hRn39Jsq3bGeI2mdhbYZbtTE18k2ZdrspkyKPMB45nc8Rj2t zWn/ifLC1tV2UhXYj494uHD4ACPCRv/4KqX16Su1TS3ARcOZcchc9rxmFDN+RrIl faoh+ybFvmDBFFjmbhP4mf/eQeWRttfWEYz9y2TJTOQKMEbpYy/c3PFX8FQrHaz6 +xXW2UvjQ1S2A1zM7XSLWCiAIYO7cVtu5LNFmCkrUAh0fDzui891BteZZaVpYrqB 3Kdee9cnFLhR4+KZRXTkmH7Q1VHZoJRxWhcyLURlx/9YZ5bkx/1wLUQYo8+m12Qm iuKHpsTjElpLmFqGG00n1C9uoOYEUQ== =TZJp -----END PGP SIGNATURE----- --mNw8fgYOgCi8R7Nz--