On Mon, Oct 06, 2014 at 02:06:56PM -0600, Eric Blake wrote:
https://bugzilla.redhat.com/show_bug.cgi?id=1147639 is an example of a downstream distro's dilemma - when backporting a feature that is implemented in an ABI-compatible manner (no .so bump was required) but where the feature involves new bits to be defined in a flags variable, how does one write code to reliably detect that those bits have been backported?
My answer would be that distros shouldn't be cherry-picking bits of the public header file at all so they don't create these non-standard APIs.
The solution presented here is a common idiom used in a number of other header files (for example, glibc's /usr/include/langinfo.h does it for ABDAY_1 and friends); by adding a self-referential preprocessor macro, client code can easily do:
| switch (state) { | #ifdef VIR_DOMAIN_PMSUSPENDED | case VIR_DOMAIN_PMSUSPENDED: | .... | #endif | }
rather than trying to figure out which version number introduced VIR_DOMAIN_PMSUSPENDED (v.9.11), and using that with LIBVIR_CHECK_VERSION. Of course, since 1.2.10 would be the first release where this practice is reliable, we will still see clients that target earlier libvirt doing:
| switch (state) { | #if LIBVIR_CHECK_VERSION(0, 9, 11) || defined(VIR_DOMAIN_PMSUSPENDED) | case VIR_DOMAIN_PMSUSPENDED: | .... | #endif | }
but that is still more maintainable.
* include/libvirt/libvirt.h.in (virDomainState): Expose #defines matching each enum value.
Signed-off-by: Eric Blake <eblake@redhat.com> ---
This patch is an RFC because I want confirmation that it is worth doing. Obviously, if it is desirable, there will be a LOT more addition of #define throughout the file, but as that is mostly busy-work, I want to get the idea approved first.
include/libvirt/libvirt.h.in | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in index c910b31..0baea53 100644 --- a/include/libvirt/libvirt.h.in +++ b/include/libvirt/libvirt.h.in @@ -116,13 +116,28 @@ typedef virDomain *virDomainPtr; * A domain may be in different states at a given point in time */ typedef enum { +#define VIR_DOMAIN_NOSTATE VIR_DOMAIN_NOSTATE VIR_DOMAIN_NOSTATE = 0, /* no state */ + +#define VIR_DOMAIN_RUNNING VIR_DOMAIN_RUNNING VIR_DOMAIN_RUNNING = 1, /* the domain is running */ + +#define VIR_DOMAIN_BLOCKED VIR_DOMAIN_BLOCKED VIR_DOMAIN_BLOCKED = 2, /* the domain is blocked on resource */ + +#define VIR_DOMAIN_PAUSED VIR_DOMAIN_PAUSED VIR_DOMAIN_PAUSED = 3, /* the domain is paused by user */ + +#define VIR_DOMAIN_SHUTDOWN VIR_DOMAIN_SHUTDOWN VIR_DOMAIN_SHUTDOWN= 4, /* the domain is being shut down */ + +#define VIR_DOMAIN_SHUTOFF VIR_DOMAIN_SHUTOFF VIR_DOMAIN_SHUTOFF = 5, /* the domain is shut off */ + +#define VIR_DOMAIN_CRASHED VIR_DOMAIN_CRASHED VIR_DOMAIN_CRASHED = 6, /* the domain is crashed */ + +#define VIR_DOMAIN_PMSUSPENDED VIR_DOMAIN_PMSUSPENDED VIR_DOMAIN_PMSUSPENDED = 7, /* the domain is suspended by guest power management */
This is pretty damn ugly IMHO. I'd only support that if it was entirely automatically generated as part of the libvirt.h.in -> libvirt.h conversion. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|