qemu/docs/interop
Hanna Czenczek 019233096c vhost-user.rst: Migrating back-end-internal state
For vhost-user devices, qemu can migrate the virtio state, but not the
back-end's internal state.  To do so, we need to be able to transfer
this internal state between front-end (qemu) and back-end.

At this point, this new feature is added for the purpose of virtio-fs
migration.  Because virtiofsd's internal state will not be too large, we
believe it is best to transfer it as a single binary blob after the
streaming phase.

These are the additions to the protocol:
- New vhost-user protocol feature VHOST_USER_PROTOCOL_F_DEVICE_STATE
- SET_DEVICE_STATE_FD function: Front-end and back-end negotiate a file
  descriptor over which to transfer the state.
- CHECK_DEVICE_STATE: After the state has been transferred through the
  file descriptor, the front-end invokes this function to verify
  success.  There is no in-band way (through the file descriptor) to
  indicate failure, so we need to check explicitly.

Once the transfer FD has been established via SET_DEVICE_STATE_FD
(which includes establishing the direction of transfer and migration
phase), the sending side writes its data into it, and the reading side
reads it until it sees an EOF.  Then, the front-end will check for
success via CHECK_DEVICE_STATE, which on the destination side includes
checking for integrity (i.e. errors during deserialization).

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20231016134243.68248-5-hreitz@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2023-11-07 03:39:10 -05:00
..
barrier.rst docs: Move the protocol part of barrier.txt into interop 2021-08-02 12:55:51 +01:00
bitmaps.rst docs/interop/bitmaps: use blockdev-backup 2021-11-09 18:20:47 +01:00
dbus-display.rst docs: add dbus-display documentation 2021-12-21 10:50:21 +04:00
dbus-vmstate.rst docs: move D-Bus VMState documentation to source XML 2021-12-21 10:50:21 +04:00
dbus.rst docs: add dbus-display documentation 2021-12-21 10:50:21 +04:00
firmware.json qapi: @foo should be used to reference, not `foo` 2023-04-28 11:48:34 +02:00
index.rst docs/interop: Convert qmp-spec.txt to rST 2023-05-22 10:21:01 +02:00
live-block-operations.rst docs: add an introduction to the system docs 2023-02-02 11:48:18 +00:00
nbd.txt nbd/server: Add FLAG_PAYLOAD support to CMD_BLOCK_STATUS 2023-10-05 11:02:08 -05:00
parallels.txt parallels.txt: fix bitmap L1 table description 2021-03-08 14:56:54 +01:00
pr-helper.rst global: Squash 'the the' 2019-11-06 17:19:40 +01:00
prl-xml.txt docs/interop/prl-xml: description of Parallels Disk format 2018-01-22 14:02:33 +00:00
qcow2.txt qcow2: Explicit mention of padding bytes 2023-06-02 11:24:18 -05:00
qed_spec.txt docs: create interop/ subdirectory 2017-06-15 11:18:39 +02:00
qemu-ga-ref.rst docs: Remove stale TODO comments about license and version 2021-08-02 11:42:38 +01:00
qemu-ga.rst qga: Add new option --allow-rpcs 2023-07-10 15:54:40 +03:00
qemu-qmp-ref.rst docs: add an introduction to the system docs 2023-02-02 11:48:18 +00:00
qemu-storage-daemon-qmp-ref.rst docs: Remove stale TODO comments about license and version 2021-08-02 11:42:38 +01:00
qmp-spec.rst docs/interop/qmp-spec: Update error description for parsing errors 2023-05-22 10:22:29 +02:00
vhost-user-gpu.rst docs: vhost-user-gpu: add protocol changes for dmabuf modifiers 2023-09-12 10:37:01 +04:00
vhost-user.json configure: Improve OpenGL dependency detections 2021-03-04 09:35:30 +01:00
vhost-user.rst vhost-user.rst: Migrating back-end-internal state 2023-11-07 03:39:10 -05:00
vhost-vdpa.rst vhost-vdpa: introduce vhost-vdpa backend 2020-07-07 07:59:51 -04:00
virtio-balloon-stats.rst docs: reSTify virtio-balloon-stats documentation and move to docs/interop 2022-01-07 19:30:13 -05:00
vnc-ledstate-pseudo-encoding.rst docs/interop: Change the vnc-ledstate-Pseudo-encoding doc into .rst 2023-01-09 13:50:47 +01:00