Re: [Xen-devel] [PATCH] migration, xen: Fix block image lock issue on live migration

["Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>]

Adding in kwolf;  it looks sane to me; Kevin?
If I'm reading this right, this is just after the device state save.

Dave

* Anthony PERARD (anthony.perard@xxxxxxxxxx) wrote:
> When doing a live migration of a Xen guest with libxl, the images for
> block devices are locked by the original QEMU process, and this prevent
> the QEMU at the destination to take the lock and the migration fail.
> 
> From QEMU point of view, once the RAM of a domain is migrated, there is
> two QMP commands, "stop" then "xen-save-devices-state", at which point a
> new QEMU is spawned at the destination.
> 
> Release locks in "xen-save-devices-state" so the destination can takes
> them.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
> CCing libxl maintainers:
> CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  migration/savevm.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 4a88228614..69d904c179 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2263,6 +2263,20 @@ void qmp_xen_save_devices_state(const char *filename, 
> Error **errp)
>      qemu_fclose(f);
>      if (ret < 0) {
>          error_setg(errp, QERR_IO_ERROR);
> +    } else {
> +        /* libxl calls the QMP command "stop" before calling
> +         * "xen-save-devices-state" and in case of migration failure, libxl
> +         * would call "cont".
> +         * So call bdrv_inactivate_all (release locks) here to let the other
> +         * side of the migration take controle of the images.
> +         */
> +        if (!saved_vm_running) {
> +            ret = bdrv_inactivate_all();
> +            if (ret) {
> +                error_setg(errp, "%s: bdrv_inactivate_all() failed (%d)",
> +                           __func__, ret);
> +            }
> +        }
>      }
>  
>   the_end:
> -- 
> Anthony PERARD
> 
--
Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK

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