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

[Raphael Norwitz]

On Thu, Aug 27, 2020 at 8:17 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> 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.
> > 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.
>
>
> Raphael any input on this?

Just posted comments on the vhost/vhost-user-blk side. Will look at
the test code next.

>
> > 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
>
>