Re: Bug in macro LOG_MAKEPRI in syslog.h

[Rich Felker <dalias@libc.org>]

On Tue, Oct 06, 2015 at 09:06:49PM +0200, Pepe Aracil wrote:
> Hi all.
> 
> 
> Now the macro is defined as:
> #define LOG_MAKEPRI(f, p) (((f)<<3) | (p))
> And must be:
> #define LOG_MAKEPRI(f, p) ((f) | (p))
> 
> The next example posts wrong facility (LOG_LOCAL1) because LOG_LOCAL1 is
> already rotated ( #define LOG_LOCAL1   (17<<3) ).
> 
> syslog (LOG_MAKEPRI(LOG_LOCAL1, LOG_ERROR),
>         "Unable to make network connection to %s.  Error=%m", host);

LOG_MAKEPRI is not supposed to be used for this; it's not even a
standard API. The documented way to use syslog is to pass
LOG_LOCAL1|LOG_ERROR. See the specification at
http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html

I agree with your reasoning that the <<3 does not make sense, but
glibc and other historical systems, where the nonstandard macro was
copied from, do the same, and there does not seem to be any value in
offering an incompatible version of a nonstandard/legacy macro like
this. Presumably you're supposed to use LOG_FAC() first to do the >>3
if you want to use these legacy macros, as in:

LOG_MAKEPRI(LOG_FAC(LOG_LOCAL1), LOG_ERROR)

Yes this is ugly..

Rich