Re: [Libvir] [PATCH] Check availability of driver calls
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.
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Attachments:
- smime.p7s (application/x-pkcs7-signature — 3.2 KB)
- libvirt-driver-feature-20070820-2.patch (text/x-patch — 8.0 KB)