[Libvir] [PATCH] Check availability of driver calls

[Daniel Veillard]

On Mon, Aug 20, 2007 at 03:13:34PM +0100, Richard W.M. Jones wrote:
> This is a repost of a patch I sent before which adds the ability to 
> check for driver features.  This is completely internal to libvirt and 
> does not add any public APIs.
> 
> The original discussion is here:
> https://www.redhat.com/archives/libvir-list/2007-July/thread.html#00437
> and continues here:
> https://www.redhat.com/archives/libvir-list/2007-August/thread.html#00000
> 
> Daniel Veillard said:
> >> +typedef int
> >> +    (*virDrvSupportsFeature) (virConnectPtr conn, virDrvFeature 
> feature);
> >
> >I would rather use , int features) where you OR the features, allows
> >to know in one call if you get what you want or not.
> 
> My objection to that is here:
> https://www.redhat.com/archives/libvir-list/2007-August/msg00000.html

  The complexity comes if you think you need to return an array of integer.
I guess if you just consider passing an unsigned long in and back, filled
as an OR'ed bitfiled with the set of features you ask for you do 1 round trip
you still pas and return an atomic value, you just need a little bit of 
decoding work at the C level to analyze the bits in the values, but that's
won't be much more complex than a switch based on the enum, and IMHO
more reliable, because I still (sorry) consider enums in APIs to be a big
problem in C. Even if it's considered an internal API, I would avoid enums
there because of the RPC.

Daniel

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