Re: [Xen-devel] libxl: Is the nic param to libxl_network_device_add an (in)_out parameter?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-11-18 at 15:28 +0000, Euan Harris wrote:
> Hi,
> 
> If I call libxl_device_nic_add and pass in a mostly-default
> libxl_device_nic structure, the function fills in the unspecified default
> config fields with data for the NIC which it has just created:
> 
>       libxl_device_nic nic;
>       libxl_device_nic_init(&nic);
>       /* 
>          nic.devid == -1 
>          nic.mac == 00:00:00:00:00:00 
>            nic.model == null
>          etc.
>        */
> 
>       libxl_device_nic_add(ctx, domid, &nic, NULL);
>       /* 
>          nic.devid == 3 
>          nic.mac == 00:16:3e:1b:7b:12
>            nic.model == rtl8139
>          etc.
>        */
> 
> Is this behaviour an intentional part of the API which I can rely on,
> or just an artefact of the current implementation?  In other words, is
> nic meant to be an (in)_out parameter?

I believe so, yes. The comment under "Devices" in libxl.h probably ought
to be adjusted to say so explicitly.

Ian (J) -- do you agree?

>   If it's not, what is the correct
> way to find out the device ID which was allocated for the new device,
> for example?

You would have to libxl_device_<type>_list and look for it, which is
clearly suboptimal.

Ian.


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