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virtio-devices: net: add guest-announce plumbing

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Advertise `VIRTIO_NET_F_GUEST_ANNOUNCE` on virtio-net devices, surface
`VIRTIO_NET_S_ANNOUNCE` through config status, and handle
`VIRTIO_NET_CTRL_ANNOUNCE_ACK` on the control queue.

This adds the guest-visible state needed for post-migration or
post-restore announce requests; the VMM side triggering is added in
follow-up commits.

The motivation is to reduce post-migration and post-restore
connectivity gap. After a live migration or after restoring, it can
take the guest several seconds to be reachable again over the network.
With these announcements, the network path should be refreshed within a
few milliseconds.

On-behalf-of: SAP sebastian.eydam@sap.com
Signed-off-by: Sebastian Eydam <sebastian.eydam@cyberus-technology.de>
This commit is contained in:
Sebastian Eydam
2026-03-31 13:21:59 +02:00
committed by Rob Bradford
parent e17c0be127
commit 53a00c0514
9 changed files with 967 additions and 125 deletions
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14
docs/live_migration.md
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@@ -135,6 +135,18 @@ src $ ch-remote --api-socket=/tmp/api send-migration destination_url=unix:/tmp/s
When the above commands completed, the VM should be successfully
migrated to the destination machine without interrupting the workload.
### Network Announcements After Resume
After a VM resumes from migration, snapshot restore, or any other path
that restores a previously paused VM, Cloud Hypervisor asks supported
network devices to announce the VM from its new host. For `virtio-net`,
the current implementation sets `VIRTIO_NET_S_ANNOUNCE`, raises a config
interrupt, retries that request a few times in the background, and also
sends host-side RARP announcements on the TAP interfaces. A guest
re-announcement therefore only happens when the guest negotiated
`VIRTIO_NET_F_GUEST_ANNOUNCE`. For `vhost-user-net`, the current implementation
only uses the guest announcement path.
### TCP Socket Migration
If TCP socket is selected for migration, we need to consider migrating
@@ -190,6 +202,8 @@ After completing the above commands, the source VM will be migrated to
the destination host and continue running there. The source VM instance
will terminate normally. All ongoing processes and connections within
the VM should remain intact after the migration.
See [Network Announcements After Resume](#network-announcements-after-resume)
for the announcement behavior after a VM resumes.
#### Encryption

3
docs/snapshot_restore.md
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@@ -102,6 +102,9 @@ after restore completes:
At this point, the VM is fully restored and is identical to the VM which was
snapshot earlier.
See [Network Announcements After Resume](live_migration.md#network-announcements-after-resume)
for the announcement behavior after restore/resume.
Restore also supports selecting how guest memory is populated:
```bash