Re: [PATCH v1 0/7] vhost-user-blk: fix the migration issue and enhance qtests

[Michael S. Tsirkin]

On Tue, Aug 04, 2020 at 01:36:45PM +0300, Dima Stepanov wrote:
> Reference e-mail threads:
>   - https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg01509.html
>   - https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg05241.html
> 
> If vhost-user daemon is used as a backend for the vhost device, then we
> should consider a possibility of disconnect at any moment. There was a general
> question here: should we consider it as an error or okay state for the 
> vhost-user
> devices during migration process?
> I think the disconnect event for the vhost-user devices 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
> The first patch in the patchset fixes this issue by setting vhost device to 
> the
> stopped state in the disconnect handler and check it the vhost_migration_log()
> routine before returning from the function.

So I'm a bit confused. Isn't the connected state sufficient for this?
If not, adding some code comments explaining when is each flag
set would be helpful.
Thanks!

> qtest framework was updated to test vhost-user-blk functionality. The
> vhost-user-blk/vhost-user-blk-tests/migrate_reconnect test was added to 
> reproduce
> the original issue found.
> 
> Dima Stepanov (7):
>   vhost: recheck dev state in the vhost_migration_log routine
>   vhost: check queue state in the vhost_dev_set_log routine
>   tests/qtest/vhost-user-test: prepare the tests for adding new dev
>     class
>   tests/qtest/libqos/virtio-blk: add support for vhost-user-blk
>   tests/qtest/vhost-user-test: add support for the vhost-user-blk device
>   tests/qtest/vhost-user-test: add migrate_reconnect test
>   tests/qtest/vhost-user-test: enable the reconnect tests
> 
>  hw/block/vhost-user-blk.c          |  13 +-
>  hw/virtio/vhost.c                  |  39 ++++-
>  include/hw/virtio/vhost-user-blk.h |   1 +
>  tests/qtest/libqos/virtio-blk.c    |  14 ++
>  tests/qtest/vhost-user-test.c      | 291 
> +++++++++++++++++++++++++++++++------
>  5 files changed, 311 insertions(+), 47 deletions(-)
> 
> -- 
> 2.7.4