On Wed, May 11, 2011 at 14:13:29 -0600, Eric Blake wrote:
This one's tricker than the VIR_DEBUG0() removal, but the end result is still C99 compliant, and reasonable with enough comments.
* src/libvirt.c (VIR_ARG10, VIR_HAS_COMMA) (VIR_DOMAIN_DEBUG_EXPAND, VIR_DOMAIN_DEBUG_PASTE): New macros. (VIR_DOMAIN_DEBUG): Rewrite to handle one argument, moving multi-argument guts to... (VIR_DOMAIN_DEBUG_1): New macro. (VIR_DOMAIN_DEBUG0): Rename to VIR_DOMAIN_DEBUG_0. ---
This one was much tougher, because both fmt and its arguments were optional, and because the expansion does not stick fmt next to __VA_ARGS__. But the end result is still that you can blindly use VIR_DOMAIN_DEBUG with 1 or 3+ arguments, and get the right behavior automagically, instead of having to remember to call a different macro for the 1-arg case.
I specifically did not cater to the 2-arg case; that would be easy enough to support, though, if we had a reason for it.
src/libvirt.c | 67 +++++++++++++++++++++++++++++++++++++++----------------- 1 files changed, 46 insertions(+), 21 deletions(-)
diff --git a/src/libvirt.c b/src/libvirt.c index 13cb74a..79278b9 100644 --- a/src/libvirt.c +++ b/src/libvirt.c @@ -311,10 +311,26 @@ static struct gcry_thread_cbs virTLSThreadImpl = { NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL };
-/* Helper macro to print debugging information about a domain DOM, - * followed by a literal string FMT and any other printf arguments. - */ -#define VIR_DOMAIN_DEBUG(dom, fmt, ...) \ +/* Helper macros to implement VIR_DOMAIN_DEBUG using just C99. This + * assumes you pass fewer than 10 arguments to VIR_DOMAIN_DEBUG, but + * can easily be expanded if needed. */ +#define VIR_ARG10(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, ...) _10 +#define VIR_HAS_COMMA(...) VIR_ARG10(__VA_ARGS__, 1, 1, 1, 1, 1, 1, 1, 1, 0) + +/* Form the name VIR_DOMAIN_DEBUG_[01], then call that macro, + * according to how many arguments are present. Two-phase due to + * macro expansion rules. */ +#define VIR_DOMAIN_DEBUG_EXPAND(a, b, ...) \ + VIR_DOMAIN_DEBUG_PASTE(a, b, __VA_ARGS__) +#define VIR_DOMAIN_DEBUG_PASTE(a, b, ...) \ + a##b(__VA_ARGS__) + +/* Internal use only, when VIR_DOMAIN_DEBUG has one argument. */ +#define VIR_DOMAIN_DEBUG_0(dom) \ + VIR_DOMAIN_DEBUG_1(dom, "%s", "") + +/* Internal use only, when VIR_DOMAIN_DEBUG has three or more arguments. */ +#define VIR_DOMAIN_DEBUG_1(dom, fmt, ...) \ char _uuidstr[VIR_UUID_STRING_BUFLEN]; \ const char *_domname = NULL; \ \
Personally I would prefer this macro to be ``do { ... } while (0)'' but that a preexisting issue and given that it's only used at the beginning of functions I guess I can live without this modification. Heh, that's a pure ugliness. But at least it's a self-contained ugliness and serves a good purpose. ACK Jirka