vhost-user devices can get a disconnect in the middle of the VHOST-USER
handshake on the migration start. If disconnect event happened right
before sending next VHOST-USER command, then the vhost_dev_set_log()
call in the vhost_migration_log() function will return error. This error
will lead to the assert() and close the QEMU migration source process.
For the vhost-user devices the disconnect event should not break the
migration process, because:
- the device will be in the stopped state, so it will not be changed
during migration
- if reconnect will be made the migration log will be reinitialized as
part of reconnect/init process:
#0 vhost_log_global_start (listener=0x563989cf7be0)
at hw/virtio/vhost.c:920
#1 0x000056398603d8bc in listener_add_address_space (listener=0x563989cf7be0,
as=0x563986ea4340 <address_space_memory>)
at softmmu/memory.c:2664
#2 0x000056398603dd30 in memory_listener_register (listener=0x563989cf7be0,
as=0x563986ea4340 <address_space_memory>)
at softmmu/memory.c:2740
#3 0x0000563985fd6956 in vhost_dev_init (hdev=0x563989cf7bd8,
opaque=0x563989cf7e30, backend_type=VHOST_BACKEND_TYPE_USER,
busyloop_timeout=0)
at hw/virtio/vhost.c:1385
#4 0x0000563985f7d0b8 in vhost_user_blk_connect (dev=0x563989cf7990)
at hw/block/vhost-user-blk.c:315
#5 0x0000563985f7d3f6 in vhost_user_blk_event (opaque=0x563989cf7990,
event=CHR_EVENT_OPENED)
at hw/block/vhost-user-blk.c:379
Update the vhost-user-blk device with the internal started_vu field which
will be used for initialization (vhost_user_blk_start) and clean up
(vhost_user_blk_stop). This additional flag in the VhostUserBlk structure
will be used to track whether the device really needs to be stopped and
cleaned up on a vhost-user level.
The disconnect event will set the overall VHOST device (not vhost-user) to
the stopped state, so it can be used by the general vhost_migration_log
routine.
Such approach could be propogated to the other vhost-user devices, but
better idea is just to make the same connect/disconnect code for all the
vhost-user devices.
This migration issue was slightly discussed earlier:
- https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg01509.html
- https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg05241.html
Signed-off-by: Dima Stepanov <dimastep@yandex-team.ru>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <9fbfba06791a87813fcee3e2315f0b904cc6789a.1599813294.git.dimastep@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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