debug: Avoid debug header being separated from debug text

Currently the file backend can produce something like:

  HEADER1 HEADER2  TEXT2
    TEXT1

when different processes try to log at the same time.

Avoid this by writing the header and text at the same time using
writev().  This means that the header always has to be written by the
backend, so update all backends to do this.

The non-file backends should behave as before when they were invoked
separately to render the header.  It might be possible to optimise
some of them (e.g. via sd_journal_sendv) but this requires more
investigation (e.g. sd_journal_sendv()'s handling of newlines) and is
beyond the scope of this change.

state.header_str_no_nl takes the place of msg_no_nl for the header,
since some of the backends need the no-newline version.  It is handled
the same was as msg_no_nl: produce the no_nl version exactly once,
whether or not it is needed, since this is better than repeating it in
several backends.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Volker Lendecke <vl@samba.org>

lib/util/debug.c

@@ -96,6 +96,7 @@ static struct {
 	debug_callback_fn callback;
 	void *callback_private;
 	char header_str[300];
+	char header_str_no_nl[300];
 	size_t hs_len;
 } state = {
 	.settings = {
@@ -232,6 +233,16 @@ static void copy_no_nl(char *out,
 static void debug_file_log(int msg_level,
 			   const char *msg, const char *msg_no_nl)
 {
+	struct iovec iov[] = {
+		{
+			.iov_base = discard_const(state.header_str),
+			.iov_len = state.hs_len,
+		},
+		{
+			.iov_base = discard_const(msg),
+			.iov_len = strlen(msg),
+		},
+	};
 	ssize_t ret;
 	int fd;
 
@@ -244,7 +255,7 @@ static void debug_file_log(int msg_level,
 	}
 
 	do {
-		ret = write(fd, msg, strlen(msg));
+		ret = writev(fd, iov, ARRAY_SIZE(iov));
 	} while (ret == -1 && errno == EINTR);
 }
 
@@ -284,6 +295,9 @@ static void debug_syslog_log(int msg_level,
 	 */
 	priority |= SYSLOG_FACILITY;
 
+	if (state.hs_len > 0) {
+		syslog(priority, "%s", state.header_str);
+	}
 	syslog(priority, "%s", msg);
 }
 #endif /* WITH_SYSLOG */
@@ -293,6 +307,15 @@ static void debug_syslog_log(int msg_level,
 static void debug_systemd_log(int msg_level,
 			      const char *msg, const char *msg_no_nl)
 {
+	if (state.hs_len > 0) {
+		sd_journal_send("MESSAGE=%s",
+				state.header_str_no_nl,
+				"PRIORITY=%d",
+				debug_level_to_priority(msg_level),
+				"LEVEL=%d",
+				msg_level,
+				NULL);
+	}
 	sd_journal_send("MESSAGE=%s", msg_no_nl,
 			"PRIORITY=%d", debug_level_to_priority(msg_level),
 			"LEVEL=%d", msg_level,
@@ -305,6 +328,9 @@ static void debug_systemd_log(int msg_level,
 static void debug_lttng_log(int msg_level,
 			    const char *msg, const char *msg_no_nl)
 {
+	if (state.hs_len > 0) {
+		tracef(state.header_str_no_nl);
+	}
 	tracef(msg_no_nl);
 }
 #endif /* WITH_LTTNG_TRACEF */
@@ -337,6 +363,9 @@ static void debug_gpfs_reload(bool enabled, bool previously_enabled,
 static void debug_gpfs_log(int msg_level,
 			   const char *msg, const char *msg_no_nl)
 {
+	if (state.hs_len > 0) {
+		gpfswrap_add_trace(msg_level, state.header_str_no_nl);
+	}
 	gpfswrap_add_trace(msg_level, msg_no_nl);
 }
 #endif /* HAVE_GPFS */
@@ -422,6 +451,9 @@ static void debug_ringbuf_log(int msg_level,
 			      const char *msg,
 			      const char *msg_no_nl)
 {
+	if (state.hs_len > 0) {
+		_debug_ringbuf_log(msg_level, state.header_str);
+	}
 	_debug_ringbuf_log(msg_level, msg);
 }
 
@@ -603,6 +635,9 @@ static void debug_backends_log(const char *msg, int msg_level)
 			debug_backends[i].log(msg_level, msg, msg_no_nl);
 		}
 	}
+
+	/* Only log the header once */
+	state.hs_len = 0;
 }
 
 int debuglevel_get_class(size_t idx)
@@ -1418,7 +1453,7 @@ void check_log_size( void )
 
 /*************************************************************************
  Write an debug message on the debugfile.
- This is called by dbghdr() and format_debug_text().
+ This is called by format_debug_text().
 ************************************************************************/
 
 static void Debug1(const char *msg)
@@ -1540,7 +1575,7 @@ bool dbgsetclass(int level, int cls)
 }
 
 /***************************************************************************
- Print a Debug Header.
+ Put a Debug Header into header_str.
 
  Input:  level    - Debug level of the message (not the system-wide debug
                     level. )
@@ -1686,7 +1721,10 @@ full:
 		state.hs_len = sizeof(state.header_str) - 1;
 	}
 
-	(void)Debug1(state.header_str);
+	copy_no_nl(state.header_str_no_nl,
+		   sizeof(state.header_str_no_nl),
+		   state.header_str,
+		   state.hs_len);
 
 	errno = old_errno;
 	return( true );