| Message ID | 20231004125904.110781-1-hreitz@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | vhost-user: Back-end state migration | expand |
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 > > v1: > https://lists.nongnu.org/archive/html/qemu-devel/2023-04/msg01575.html > > v2: > https://lists.nongnu.org/archive/html/qemu-devel/2023-07/msg02604.html > > v3: > https://lists.nongnu.org/archive/html/qemu-devel/2023-09/msg03750.html > > > Based-on: <20231004014532.1228637-1-stefanha@redhat.com> > ([PATCH v2 0/3] vhost: clean up device reset) > > > Hi, > > 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 > > Changes in detail: > > - 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’s RESET_DEVICE or [GS]ET_FEATURES. > 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. > > - 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. > > - Patch 3: This one’s 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 > “enabled/disabled when started” go away. Basically, I found this > change alone is enough to remove the confusion I had with the existing > documentation. > > - 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’s does, so we can define the > suspended state to be when all vrings are stopped. > > - Patch 5: Reference the suspended state. > > - Patches 6 through 8: Unmodified, except for them being rebase on > Stefan’s series. > > > 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 > > 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(-) > > -- > 2.41.0 >
RFC: https://lists.nongnu.org/archive/html/qemu-devel/2023-03/msg04263.html v1: https://lists.nongnu.org/archive/html/qemu-devel/2023-04/msg01575.html v2: https://lists.nongnu.org/archive/html/qemu-devel/2023-07/msg02604.html v3: https://lists.nongnu.org/archive/html/qemu-devel/2023-09/msg03750.html Based-on: <20231004014532.1228637-1-stefanha@redhat.com> ([PATCH v2 0/3] vhost: clean up device reset) Hi, 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. Changes in detail: - 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’s RESET_DEVICE or [GS]ET_FEATURES. 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. - 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. - Patch 3: This one’s 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 “enabled/disabled when started” go away. Basically, I found this change alone is enough to remove the confusion I had with the existing documentation. - 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’s does, so we can define the suspended state to be when all vrings are stopped. - Patch 5: Reference the suspended state. - Patches 6 through 8: Unmodified, except for them being rebase on Stefan’s series. 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 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(-)