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

[Eric Blake]

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 at 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 */

-- 
1.9.3