[libvirt] [PATCH 2/3] build: drop need for VIR_DOMAIN_DEBUG0()

[Jiri Denemark]

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