[libvirt] [python PATCH] build: make it easier to backport event ids

Eric Blake eblake at redhat.com
Thu Jan 15 15:52:44 UTC 2015

On 01/15/2015 03:51 AM, Jiri Denemark wrote:
> On Thu, Jan 15, 2015 at 10:42:39 +0000, Daniel Berrange wrote:
>> On Wed, Jan 14, 2015 at 08:08:16PM -0700, Eric Blake wrote:
>>> In some cases, it is very easy for downstream distros to backport
>>> enum values without requiring a .so bump.  Keying the conditional
>>> code off of the upstream version where the enum value was added
>>> is not ideal, because downstream then has to patch that the feature
>>> is available in their build that still reports an earlier version
>>> number.  For example, if RHEL 7 backports events from 1.2.11 into
>>> a build based on 1.2.8, building the python bindings would warn:

>>> +    if name.startswith('VIR_DOMAIN_EVENT_ID_') or name.startswith('VIR_NETWORK_EVENT_ID_'):
>>> +        event_ids.append(name)
>> If you use brackets you can break the line without confusing
>> python eg
>>     if (name.startswith('VIR_DOMAIN_EVENT_ID_') or
>>         name.startswith('VIR_NETWORK_EVENT_ID_')):


>>> +        # Write define wrappers around event id enums
>>> +        include.write("\n")
>>> +        for event_id in event_ids:
>>> +            include.write("#define %s %s\n" % (event_id, event_id))
>> I'm not seeing the point of adding this define ?
> ...
>>> -#if LIBVIR_CHECK_VERSION(0, 10, 0)
> Without that define, you can't check for the events using ifdef,
> C preprocessor doesn't see enum items.

Correct.  Creating self-referential macros is the canonical way to
convert enums into something that can be probed at preprocessor time for
using conditional compilation.  Since we have one macro for every enum
that we read from the xml of the libvirt we are targetting, we can make
the bindings support exactly the set of enum values that were backported
into the particular libvirt, without having to worry about backporting
crossing version number checks.

So does this count as an ACK with the long line fixed?

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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