On Tue, Sep 08, 2020 at 03:25:20PM +0100, Stefan Hajnoczi wrote: > On Fri, Sep 04, 2020 at 12:31:13PM +0300, Dima Stepanov wrote: > > 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 <dimas...@yandex-team.ru> > > Reviewed-by: Raphael Norwitz <raphael.norw...@nutanix.com> > > --- > > hw/block/vhost-user-blk.c | 19 ++++++++++++++++--- > > hw/virtio/vhost.c | 27 ++++++++++++++++++++++++--- > > include/hw/virtio/vhost-user-blk.h | 10 ++++++++++ > > 3 files changed, 50 insertions(+), 6 deletions(-) > > > > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c > > index 39aec42..a076b1e 100644 > > --- a/hw/block/vhost-user-blk.c > > +++ b/hw/block/vhost-user-blk.c > > @@ -150,6 +150,7 @@ static int vhost_user_blk_start(VirtIODevice *vdev) > > error_report("Error starting vhost: %d", -ret); > > goto err_guest_notifiers; > > } > > + s->started_vu = true; > > > > /* guest_notifier_mask/pending not used yet, so just unmask > > * everything here. virtio-pci will do the right thing by > > @@ -175,6 +176,11 @@ static void vhost_user_blk_stop(VirtIODevice *vdev) > > VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus); > > int ret; > > > > + if (!s->started_vu) { > > + return; > > + } > > + s->started_vu = false; > > + > > if (!k->set_guest_notifiers) { > > return; > > } > > @@ -341,9 +347,7 @@ static void vhost_user_blk_disconnect(DeviceState *dev) > > } > > s->connected = false; > > > > - if (s->dev.started) { > > - vhost_user_blk_stop(vdev); > > - } > > + vhost_user_blk_stop(vdev); > > > > vhost_dev_cleanup(&s->dev); > > } > > @@ -399,6 +403,15 @@ static void vhost_user_blk_event(void *opaque, > > QEMUChrEvent event) > > NULL, NULL, false); > > aio_bh_schedule_oneshot(ctx, vhost_user_blk_chr_closed_bh, > > opaque); > > } > > + > > + /* > > + * Move vhost device to the stopped state. The vhost-user device > > + * will be clean up and disconnected in BH. This can be useful in > > + * the vhost migration code. If disconnect was caught there is an > > + * option for the general vhost code to get the dev state without > > + * knowing its type (in this case vhost-user). > > + */ > > + s->dev.started = false; > > break; > > case CHR_EVENT_BREAK: > > case CHR_EVENT_MUX_IN: > > Hi Dima, > Is it possible to move this logic into the vhost_*() API so that all > devices benefit from it? This seems like a generic vhost-user issue > rather than a vhost-user-blk issue. > > In other words, it would be great if the vhost APIs in QEMU are designed > in a way so that the user doesn't need to think about this. > > Stefan
Hi Stefan, Yes, i also think that it is a right direction, to have some vhost/vhost-user API here. In this case we will be able to share the code between all the vhost-user devices, which is important. We had the same conclusion in this e-mail thread: https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg06955.html When we backported the fix from the vhost-user-net device to vhost-user-blk and also provided some additional logic only for the vhost-user-blk device. So my idea is, first fix two issues: - vhost-user-blk reconnect issue (already merged) - vhost-user-blk migration issue (this patchset) After it try to review current implementation, so for example the unix socket logic could be shared between all the vhost-user devices. Maybe something else could be done here. Dima.
