[Libguestfs] [libnbd PATCH 1/3] generator: Introduce REnum/RFlags return types

[Eric Blake]

On 9/7/20 9:52 AM, Richard W.M. Jones wrote:

>>> You used unsigned for RFlags, but shouldn't it be this instead?
>>>
>>> +  | RFlags (_) -> "uint32_t"
>>
>> Hmm.  For Flags as input, we take uint32_t, but for
>> get_handshake_flags which used to return RUint, we returned
>> unsigned; as written, my patch preserved generated code in its
>> entirety.  Changing it to return uint32_t makes sense, but is a
>> minor API change.
> 
> Oh I see, good point.
> 
> I think although technically it might not be an ABI change,
> best to leave it as you wrote it.

Not only is it not an ABI change, but we got lucky: no one has ever 
compiled libnbd on a platform where it would be an API change.  Note 
that pre-patch, our generated lib/unlocked.h had 'unsigned 
nbd_get_handshake_flags' but our hand-written lib/handle.c had 'uint32_t 
nbd_get_handshake_flags'.  On every platform where libnbd compiles, the 
two types are synonymous, so the API change factor is a non-issue 
(platforms where it might not be the same could be a 32-bit platform 
where 'uint32_t' is 'long', but no one has reported trying to build 
libnbd on such a system).  So I'll go ahead and make the change, with 
the commit message giving this additional justification.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org