Re: [libvirt] [RFC PATCH] include: make it easier to probe enum growth

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?

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(a)redhat.com&gt; --- 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 */