Re: [Xen-devel] libxl_device handling for nic and vtmp

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Feb 18, 2016 at 04:13:21PM +0100, Olaf Hering wrote:
> What is the point of libxl__update_config_nic and
> libxl__update_config_vtmp?
> 
> In libxl__device_type_add (called from DEFINE_DEVICE_ADD) the input
> type is copied with libxl_device_type_copy to type_saved, which is a
> 1:1 copy. If needed, a new devid is assigned to the input. Later the
> copy is updated with one of the two helper functions mentioned above.
> But the helpers do not only update devid, also mac or uuid.
> 
> To me it looks like the double assignment can be removed. The new
> pvusb code does not do it this way, it makes a copy of the fully
> initialized type.
> 
> Perhaps the two helpers are useful in the context of domcreate_complete,
> I have not reviewed that part of the code.
> 

Because in the process of domain building some configurations are
autogenerated and you want to preserve them.

For example, user might not have specified mac address so the library
generates one for (s)he. You don't want mac address to regenerate after
save / restore or migration.  But you don't want to preserve all
autogenerated state, so you use the original copy as template and fill
it up as you see fit.

BTW, I look at my inbox far more often than I look at xen-devel so if
you CC me (relevant maintainers in general) in relevant emails in the
future they are less likely to fall through the crack.

Wei.

> 
> Olaf
> 
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