On 19/12/2024 12:13, Laurent Vivier wrote:
This series allows a QEMU guest to be migrated while it is connected to Passt using vhost-user interface.
There are two parts:
- first part enables the migration of QEMU without transferring the internal state of Passt. All connections are lost.
This is done by implementing VHOST_USER_SET_LOG_FD and VHOST_USER_SET_LOG_BASE commands (and enabling VHOST_USER_PROTOCOL_F_LOG_SHMFD feature)
"vhost-user: add VHOST_USER_SET_LOG_FD command" "vhost-user: add VHOST_USER_SET_LOG_BASE command" "vhost-user: Report to front-end we support VHOST_USER_PROTOCOL_F_LOG_SHMFD"
- second part allows source Passt instance to send its internal state using QEMU migration channel to destination Passt instance.
This is done implementing VHOST_USER_SET_DEVICE_STATE_FD and VHOST_USER_CHECK_DEVICE_STATE (and enabling VHOST_USER_PROTOCOL_F_DEVICE_STATE feature).
"vhost-user: add VHOST_USER_CHECK_DEVICE_STATE command" "vhost-user: add VHOST_USER_SET_DEVICE_STATE_FD command" "vhost-user: Report to front-end we support VHOST_USER_PROTOCOL_F_DEVICE_STATE"
For now, it only implements the function needed to transfer the state but no state is transferred.
VHOST_USER_PROTOCOL_F_DEVICE_STATE is implemented in QEMU only for vhost-user-fs, to be able to use it with virtio-net I have proposed a patch upstream:
https://patchew.org/QEMU/20241218143453.1573185-1-lvivier@redhat.com/
Laurent Vivier (9): virtio: Use const pointer for vu_dev vhost-user: update protocol features and commands list vhost-user: add VHOST_USER_SET_LOG_FD command vhost-user: Pass vu_dev to more virtio functions vhost-user: add VHOST_USER_SET_LOG_BASE command vhost-user: Report to front-end we support VHOST_USER_PROTOCOL_F_LOG_SHMFD vhost-user: add VHOST_USER_CHECK_DEVICE_STATE command vhost-user: add VHOST_USER_SET_DEVICE_STATE_FD command vhost-user: Report to front-end we support VHOST_USER_PROTOCOL_F_DEVICE_STATE
epoll_type.h | 2 + passt.c | 4 + util.h | 3 + vhost_user.c | 251 ++++++++++++++++++++++++++++++++++++++++++++++++++- vhost_user.h | 50 +++++++++- virtio.c | 116 +++++++++++++++++++++--- virtio.h | 32 +++++-- vu_common.c | 59 +++++++++++- vu_common.h | 3 +- 9 files changed, 484 insertions(+), 36 deletions(-)
Another point: vhost-user can ask backend (passt) to send a notification at the end of the migration on the destination side to the network to update the network topology. Do we need this? This is VHOST_USER_SEND_RARP: "Ask vhost user back-end to broadcast a fake RARP to notify the migration is terminated for guest that does not support GUEST_ANNOUNCE. Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in VHOST_USER_GET_FEATURES and protocol feature bit VHOST_USER_PROTOCOL_F_RARP is present in VHOST_USER_GET_PROTOCOL_FEATURES. The first 6 bytes of the payload contain the mac address of the guest to allow the vhost user back-end to construct and broadcast the fake RARP." GUEST_ANNOUNCE is a feature that allows vhost-user to ask the kernel to send the notification itself at the end of the migration. Thanks, Laurent