logging: add error argument to _nm_log() to support "%m" format specifier

A gnu extension to printf adds the format specifier "%m"
to print @errno. To preserve the error number until the
point where the logging statement is constructed, pass
it as an additional argument to _nm_log().

This is not (yet) used from NM internal code. But systemd is adding
similar functionality to its logging functions. Add the same also to
nm-logging, to support systemd's usage of "%m".

(cherry picked from commit 5162426d41)

src/dhcp-manager/systemd-dhcp/nm-sd-adapt.h

@@ -57,7 +57,7 @@ G_STMT_START { \
 	if (nm_logging_enabled (_l, LOGD_DHCP)) { \
 		const char *_location = strrchr (file "", '/'); \
 		\
-		_nm_log (_location ? _location + 1 : file, line, func, _l, LOGD_DHCP, format, ## __VA_ARGS__); \
+		_nm_log (_location ? _location + 1 : file, line, func, _l, LOGD_DHCP, 0, format, ## __VA_ARGS__); \
 	} \
 } G_STMT_END
 

src/nm-logging.c

@@ -362,6 +362,7 @@ _nm_log (const char *file,
          const char *func,
          NMLogLevel level,
          NMLogDomain domain,
+         int error,
          const char *fmt,
          ...)
 {
@@ -379,6 +380,10 @@ _nm_log (const char *file,
 	if (!(logging[level] & domain))
 		return;
 
+	/* Make sure that %m maps to the specified error */
+	if (error != 0)
+		errno = error;
+
 	va_start (args, fmt);
 	msg = g_strdup_vprintf (fmt, args);
 	va_end (args);

src/nm-logging.h

@@ -105,7 +105,7 @@ typedef enum  { /*< skip >*/
 #define nm_log(level, domain, ...) \
     G_STMT_START { \
         if (nm_logging_enabled ((level), (domain))) { \
-            _nm_log (__FILE__, __LINE__, G_STRFUNC, (level), (domain), __VA_ARGS__); \
+            _nm_log (__FILE__, __LINE__, G_STRFUNC, (level), (domain), 0, __VA_ARGS__); \
         } \
     } G_STMT_END
 
@@ -141,8 +141,9 @@ void _nm_log (const char *file,
               const char *func,
               NMLogLevel level,
               NMLogDomain domain,
+              int error,
               const char *fmt,
-              ...) __attribute__((__format__ (__printf__, 6, 7)));
+              ...) __attribute__((__format__ (__printf__, 7, 8)));
 
 const char *nm_logging_level_to_string (void);
 const char *nm_logging_domains_to_string (void);