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Implement %m in src/port/snprintf.c, and teach elog.c to rely on that.

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I started out with the idea that we needed to detect use of %m format specs
in contexts other than elog/ereport calls, because we couldn't rely on that
working in *printf calls.  But a better answer is to fix things so that it
does work.  Now that we're using snprintf.c all the time, we can implement
%m in that and we've fixed the problem.

This requires also adjusting our various printf-wrapping functions so that
they ensure "errno" is preserved when they call snprintf.c.

Remove elog.c's handmade implementation of %m, and let it rely on
snprintf to support the feature.  That should provide some performance
gain, though I've not attempted to measure it.

There are a lot of places where we could now simplify 'printf("%s",
strerror(errno))' into 'printf("%m")', but I'm not in any big hurry
to make that happen.

Patch by me, reviewed by Michael Paquier

Discussion: https://postgr.es/m/2975.1526862605@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2018-09-26 13:31:56 -04:00
parent 96bf88d527
commit d6c55de1f9
8 changed files with 57 additions and 67 deletions
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6
src/backend/lib/stringinfo.c
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@ -77,12 +77,15 @@ resetStringInfo(StringInfo str)
void
appendStringInfo(StringInfo str, const char *fmt,...)
{
int save_errno = errno;
for (;;)
{
va_list args;
int needed;
/* Try to format the data. */
errno = save_errno;
va_start(args, fmt);
needed = appendStringInfoVA(str, fmt, args);
va_end(args);
@ -105,6 +108,9 @@ appendStringInfo(StringInfo str, const char *fmt,...)
* pass the return value to enlargeStringInfo() before trying again; see
* appendStringInfo for standard usage pattern.
*
* Caution: callers must be sure to preserve their entry-time errno
* when looping, in case the fmt contains "%m".
*
* XXX This API is ugly, but there seems no alternative given the C spec's
* restrictions on what can portably be done with va_list arguments: you have
* to redo va_start before you can rescan the argument list, and we can't do