Re: [Libvir] PATCH: 5/10: public auth callback API

On Tue, Dec 04, 2007 at 10:46:50AM -0500, Daniel Veillard wrote: > On Tue, Dec 04, 2007 at 12:57:39PM +0000, Richard W.M. Jones wrote: > > Daniel P. Berrange wrote: > > > virConnectPtr virConnectOpenAuth (const char *name, > > > virConnectAuthPtr auth, > > > int flags); > > > > I'm a fan of callers passing in the size of the structure (as they see > > it). Allows the structure to be expanded in future, and if done right > > can allow both forwards and backwards compatibility. > > > > cf: http://www.libvirt.org/html/libvirt-libvirt.html#virDomainInterfaceStats > > Hum, honnestly, that's not my preferred way. If you really think there > should be room for expansion, I would either: > - add a version number to the structure and allocator/destructor > functions as part of the API (prefered) This adds more complexity and the single sizeof(*auth) param IMHO.

> - add padding at tyhe end of the structure which could allow > a future growth > adding the size of the structure as the argument moves the complexity away > from the library implementor to the library user, It doesn't really - the user just has to add sizeof(*auth) as an arg and all the rest of the complexity is in the library internals.

In fact it doesn't need to add any complexity, because we could make it a compile time macro #define virConnectOpenAuth(name,auth,flags) virConnectOpenAuth(name,auth,sizeof(*auth),flags)