Daniel Veillard wrote:
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
This doesn't work though, because different parts of the system have to answer different parts of a request such as: VIR_DRV_FEATURE_MIGRATION_V1 | VIR_DRV_FEATURE_REMOTE. VIR_DRV_FEATURE_MIGRATION_V1 goes through to end driver. VIR_DRV_FEATURE_REMOTE is answered by the local end of remote (src/remote_internal.c). My real point is I don't understand the case where it is ever useful to query more than one feature.
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.
I meant to get rid of the enums. Attached is a version which uses macros instead so the type should always be 'int' (ie. ABI stable). Rich. -- Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/ Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 03798903