Fix syslogger's rotation disable/re-enable logic.

If it fails to open a new log file, the syslogger assumes there's something
wrong with its parameters (such as log_directory), and stops attempting
automatic time-based or size-based log file rotations.  Sending it SIGHUP
is supposed to start that up again.  However, the original coding for that
was really bogus, involving clobbering a couple of GUC variables and hoping
that SIGHUP processing would restore them.  Get rid of that technique in
favor of maintaining a separate flag showing we've turned rotation off.
Per report from Mark Kirkwood.

Also, the syslogger will automatically attempt to create the log_directory
directory if it doesn't exist, but that was only happening at startup.
For consistency and ease of use, it should do the same whenever the value
of log_directory is changed by SIGHUP.

Back-patch to all supported branches.

src/backend/postmaster/syslogger.c

@@ -87,6 +87,7 @@ extern bool redirection_done;
  */
 static pg_time_t next_rotation_time;
 static bool pipe_eof_seen = false;
+static bool rotation_disabled = false;
 static FILE *syslogFile = NULL;
 static FILE *csvlogFile = NULL;
 static char *last_file_name = NULL;
@@ -317,6 +318,11 @@ SysLoggerMain(int argc, char *argv[])
 				pfree(currentLogDir);
 				currentLogDir = pstrdup(Log_directory);
 				rotation_requested = true;
+
+				/*
+				 * Also, create new directory if not present; ignore errors
+				 */
+				mkdir(Log_directory, S_IRWXU);
 			}
 			if (strcmp(Log_filename, currentLogFilename) != 0)
 			{
@@ -334,9 +340,19 @@ SysLoggerMain(int argc, char *argv[])
 				currentLogRotationAge = Log_RotationAge;
 				set_next_rotation_time();
 			}
+
+			/*
+			 * If we had a rotation-disabling failure, re-enable rotation
+			 * attempts after SIGHUP, and force one immediately.
+			 */
+			if (rotation_disabled)
+			{
+				rotation_disabled = false;
+				rotation_requested = true;
+			}
 		}
 
-		if (!rotation_requested && Log_RotationAge > 0)
+		if (!rotation_requested && Log_RotationAge > 0 && !rotation_disabled)
 		{
 			/* Do a logfile rotation if it's time */
 			pg_time_t	now = time(NULL);
@@ -345,7 +361,7 @@ SysLoggerMain(int argc, char *argv[])
 				rotation_requested = time_based_rotation = true;
 		}
 
-		if (!rotation_requested && Log_RotationSize > 0)
+		if (!rotation_requested && Log_RotationSize > 0 && !rotation_disabled)
 		{
 			/* Do a rotation if file is too big */
 			if (ftell(syslogFile) >= Log_RotationSize * 1024L)
@@ -1107,8 +1123,7 @@ logfile_rotate(bool time_based_rotation, int size_rotation_for)
 			{
 				ereport(LOG,
 						(errmsg("disabling automatic rotation (use SIGHUP to reenable)")));
-				Log_RotationAge = 0;
-				Log_RotationSize = 0;
+				rotation_disabled = true;
 			}
 
 			if (filename)
@@ -1165,8 +1180,7 @@ logfile_rotate(bool time_based_rotation, int size_rotation_for)
 			{
 				ereport(LOG,
 						(errmsg("disabling automatic rotation (use SIGHUP to reenable)")));
-				Log_RotationAge = 0;
-				Log_RotationSize = 0;
+				rotation_disabled = true;
 			}
 
 			if (filename)