Re: [Xen-devel] [PATCH 28/28] libxl: ocaml: provide default records for libxl types

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-03-25 at 14:45 +0000, Rob Hoes wrote:
> Libxl functions such as libxl_domain_create_new take large structs
> of configuration parameters. Often, we would like to use the default
> values for many of these parameters.
> 
> This commit makes OCaml records of defaults available for all libxl
> struct and keyed-union types, which can be used as a base to construct
> your own records, and to selectively override parameters where needed.
> 
> For example, a Domain_create_info record can now be created as follows:
> 
> let c_info = Xenlight.Domain_create_info.({ default with
>       ty = Xenlight.DOMAIN_TYPE_PV;
>       name = Some vm_name;
>       uuid = vm_uuid;
> }) in

This is a clever approach (and I expect good idiomatic ocaml?) but you
need to handle the init_val IDL field for all types since not everything
should be set to zero (e.g. some of the UInt subtypes don't default to
0, see MemKB for one).

I wonder if a better alternative might be to use a C binding to call
libxl_TYPE_init() and convert that to an ocaml value? This would mean
one less place to change in the future as well.

Ian.


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