Re: [PATCH] implement the LOG_PERROR option in syslog

[Rich Felker <dalias@libc.org>]

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On Fri, Jul 11, 2014 at 12:49:50AM -0400, Rich Felker wrote:
> Anyway, for adding the feature you want, where you just want to know
> the number of initial bytes to skip writing to stderr, I would just
> use %n to get the offset.

Attached is a patch to do this. I'll commit it soon if nobody notices
any problems right away.

Rich

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diff --git a/src/misc/syslog.c b/src/misc/syslog.c
index 57f1d75..d2ea4aa 100644
--- a/src/misc/syslog.c
+++ b/src/misc/syslog.c
@@ -80,6 +80,7 @@ static void _vsyslog(int priority, const char *message, va_list ap)
 	int errno_save = errno;
 	int pid;
 	int l, l2;
+	int hlen;
 
 	if (log_fd < 0) {
 		__openlog();
@@ -93,8 +94,8 @@ static void _vsyslog(int priority, const char *message, va_list ap)
 	strftime(timebuf, sizeof timebuf, "%b %e %T", &tm);
 
 	pid = (log_opt & LOG_PID) ? getpid() : 0;
-	l = snprintf(buf, sizeof buf, "<%d>%s %s%s%.0d%s: ",
-		priority, timebuf, log_ident, "["+!pid, pid, "]"+!pid);
+	l = snprintf(buf, sizeof buf, "<%d>%s %n%s%s%.0d%s: ",
+		priority, timebuf, &hlen, log_ident, "["+!pid, pid, "]"+!pid);
 	errno = errno_save;
 	l2 = vsnprintf(buf+l, sizeof buf - l, message, ap);
 	if (l2 >= 0) {
@@ -102,6 +103,7 @@ static void _vsyslog(int priority, const char *message, va_list ap)
 		else l += l2;
 		if (buf[l-1] != '\n') buf[l++] = '\n';
 		send(log_fd, buf, l, 0);
+		if (log_opt & LOG_PERROR) write(2, buf+hlen, l-hlen);
 	}
 }