[libvirt] [PATCH] libxl: Fix devid init in libxlMakeNicList

[Jim Fehlig]

Stefan Bader wrote: 
> This basically reverts commit ba64b97134a6129a48684f22f31be92c3b6eef96
> "libxl: Allow libxl to set NIC devid". However assigning devid's
> before calling libxlMakeNic does not work as that is calling
> libxl_device_nic_init which sets it back to -1.
> Right now auto-assignment only works in the hotplug case. But even if
> that would be fixed at some point (if that is possible at all), this
> would add a weird dependency between Xen and libvirt versions.

Yeah, I had numerous inquires and bugs come my way even after fixing vfb and
vkb devid initialization in libxl with xen.git commit 5420f265.  It took
some time for the fix to make its way to downstream users.  Since there is
not yet a fix in Xen, it only makes sense to do the nic devid initialization
in libvirt to fix PXE booting HVM domains.

> The change here should accept any auto-assignment that makes it into
> libxl_device_nic_init. My understanding is that a caller always is
> allowed to make the devid choice itself. And assuming libxlMakeNicList
> is only used on domain creation, a sequential numbering should be ok.
> 
> Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  src/libxl/libxl_conf.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
> index 04d01af..4cefadf 100644
> --- a/src/libxl/libxl_conf.c
> +++ b/src/libxl/libxl_conf.c
> @@ -918,6 +918,13 @@ libxlMakeNicList(virDomainDefPtr def,  
> libxl_domain_config *d_config)
>      for (i = 0; i < nnics; i++) {
>          if (libxlMakeNic(def, l_nics[i], &x_nics[i]))
>              goto error;
> +        /*
> +         * The devid (at least right now) will not get initialized by
> +         * libxl in the setup case but is required for starting the
> +         * device-model.
> +         */
> +        if (x_nics[i].devid < 0)
> +            x_nics[i].devid = i;

I think this is a better approach than the original code removed by ba64b971.
I've pushed this since it is clearly a bug fix and appropriate for 1.2.1.

Regards,
Jim

>      }
>  
>      d_config->nics = x_nics;