[Libguestfs] [libnbd PATCH] generator: Add support for namespace constants

[Eric Blake]

On 6/28/19 1:32 AM, Martin Kletzander wrote:

>> Rich still has the idea of adding a 'qemu-nbd --list' counterpart, so
>> defining a constant for the "base:" and "qemu:" namespaces makes sense
>> for that even if we can't use it now.  Hmm - your patch defines
>> LIBNBD_NAMESPACE_BASE to "base", but in practice we'd want to pass
>> "base:" when querying which contexts are available in that namespace.
>>
> 
> That is on the protocol, but the API does not need to take the ':*' suffix.
> Also it is costless to do LIBNBD_NAMESPACE_BASE ":" in the C code.

With my patch, it is currently "base:" in the header (and in the other
language bindings). I suggest that until we actually have an API for
doing listings, it doesn't really matter, we can change it to drop the
trailing ':' at that time if it proves easier to force clients to do the
string constant concatenation for using the new API at that time.


>>
>> I'd love to have LIBNBD_CONTEXT_QEMU_DIRTY_BITMAP(foo) produce the
>> string "qemu:dirty-bitmap:foo". I'm not sure how to wire that in on top
>> of your patches, so it doesn't have to happen today, but it's food for
>> thought.
>>
> 
> You mean, for example:
> 
> #define LIBNBD_CONTEXT_QEMU_DIRTY_BITMAP(foo) "qemu:dirty-bitmap:" #foo

I guess it depends on whether call-sites will look like

LIBNBD_CONTEXT_QEMU_DIRTY_BITMAP("foo")
(performing constant string concatenation)

vs.

LIBNBD_CONTEXT_QEMU_DIRTY_BITMAP(foo)
(performing runtime dynamic computation)

so the macro may have to call out to a function and reserve thread-local
storage.  It may be another thing where we tweak things based on what's
easiest to implement and easiest for clients to consume.

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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 488 bytes
Desc: OpenPGP digital signature
URL: <http://listman.redhat.com/archives/libguestfs/attachments/20190628/84d1fc19/attachment.sig>