[Libguestfs] Add support for musl libc

[Richard W.M. Jones]

On Mon, Aug 01, 2016 at 08:24:43PM +0200, Jakub Jirutka wrote:
> Hi,
>
> I’m trying to compile libguestfs on Alpine Linux, that uses musl
> libc (lightweight, fast and simple standards-conformance libc). It
> fails in the check phase due to missing glibc-style extended printf
> formatters.
> --
> checking for register_printf_specifier... no
> checking for register_printf_function... no
> configure: error: in `/tmp/libguestfs/src/libguestfs-1.32.6’:
> configure: error: No support for glibc-style extended printf formatters.
> 
> This means you either have a very old glibc (pre-2.0) or you
> are using some other libc where this is not supported.
> See `config.log’ for more details
> --
>
> Could you please add support for musl libc, i.e. avoid using
> glibc-specific extensions? How often are such non-standard functions
> used in the libguestfs code-base; can we just patch few occurrences
> or is it too widespread?

If you grep for %Q or %R you'll see the uses of these custom printf
specifiers.  They are IMHO very useful, as well as being a cool
feature of glibc.  How about adding them to musl libc?

Alternatively I notice that gnulib has an (unimplemented, sadly)
replacement register_printf_*, so that could be implemented which
would fix portability to BSD too.

It's a shame that ISO or POSIX doesn't standardize a way to do this.

Rich.

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