Re: [PATCH 2/2] failover: don't allow to migrate a paused VM that needs PCI unplug

[Michael S. Tsirkin]

On Wed, Sep 29, 2021 at 04:43:11PM +0200, Laurent Vivier wrote:
> As the guest OS is paused, we will never receive the unplug event
> from the kernel and the migration cannot continue.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Well ... what if user previously did

pause
start migration
unpause

we are breaking it now for no good reason.

Further, how about

start migration
pause

are we going to break this too? by failing pause?


> ---
>  hw/net/virtio-net.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index f205331dcf8c..e54b6c8cd86c 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -37,8 +37,10 @@
>  #include "qapi/qapi-events-migration.h"
>  #include "hw/virtio/virtio-access.h"
>  #include "migration/misc.h"
> +#include "migration/migration.h"
>  #include "standard-headers/linux/ethtool.h"
>  #include "sysemu/sysemu.h"
> +#include "sysemu/runstate.h"
>  #include "trace.h"
>  #include "monitor/qdev.h"
>  #include "hw/pci/pci.h"
> @@ -3279,7 +3281,13 @@ static void 
> virtio_net_handle_migration_primary(VirtIONet *n, MigrationState *s)
>      should_be_hidden = qatomic_read(&n->failover_primary_hidden);
>  
>      if (migration_in_setup(s) && !should_be_hidden) {
> -        if (failover_unplug_primary(n, dev)) {
> +        if (!runstate_is_running()) {
> +            Error *err = NULL;
> +            error_setg(&err,
> +                       "cannot unplug primary device while VM is paused");
> +            migration_cancel(err);
> +            error_free(err);
> +        } else if (failover_unplug_primary(n, dev)) {
>              vmstate_unregister(VMSTATE_IF(dev), qdev_get_vmsd(dev), dev);
>              qapi_event_send_unplug_primary(dev->id);
>              qatomic_set(&n->failover_primary_hidden, true);
> -- 
> 2.31.1