Improve pg_check_dir code and comments.

Avoid losing errno if readdir() fails and closedir() works.  Consistently
return 4 rather than 3 if both a lost+found directory and other files are
found, rather than returning one value or the other depending on the
order of the directory listing.  Update comments to match the actual
behavior.

These oversights date to commits 6f03927f
and 17f15239.

Marco Nenciarini

src/port/pgcheckdir.c

@@ -22,7 +22,9 @@
  * Returns:
  *		0 if nonexistent
  *		1 if exists and empty
- *		2 if exists and not empty
+ *		2 if exists and contains _only_ dot files
+ *		3 if exists and contains a mount point
+ *		4 if exists and not empty
  *		-1 if trouble accessing directory (errno reflects the error)
  */
 int
@@ -32,6 +34,8 @@ pg_check_dir(const char *dir)
 	DIR		   *chkdir;
 	struct dirent *file;
 	bool		dot_found = false;
+	bool		mount_found = false;
+	int			readdir_errno;
 
 	chkdir = opendir(dir);
 	if (chkdir == NULL)
@@ -51,10 +55,10 @@ pg_check_dir(const char *dir)
 		{
 			dot_found = true;
 		}
+		/* lost+found directory */
 		else if (strcmp("lost+found", file->d_name) == 0)
 		{
-			result = 3;			/* not empty, mount point */
-			break;
+			mount_found = true;
 		}
 #endif
 		else
@@ -64,9 +68,20 @@ pg_check_dir(const char *dir)
 		}
 	}
 
-	if (errno || closedir(chkdir))
+	if (errno)
 		result = -1;			/* some kind of I/O error? */
 
+	/* Close chkdir and avoid overwriting the readdir errno on success */
+	readdir_errno = errno;
+	if (closedir(chkdir))
+		result = -1;			/* error executing closedir */
+	else
+		errno = readdir_errno;
+
+	/* We report on mount point if we find a lost+found directory */
+	if (result == 1 && mount_found)
+		result = 3;
+
 	/* We report on dot-files if we _only_ find dot files */
 	if (result == 1 && dot_found)
 		result = 2;