[PATCH] Add commit=0 to ext3, meaning "set commit to default".

From: Bart Samwel <bart@samwel.tk>

Add support for the value "0" to ext3's "commit" option.  When this value
is given, ext3 substitutes it by the default commit interval.  Introduce a
constant JBD_DEFAULT_MAX_COMMIT_AGE for this.

fs/ext3/super.c

@@ -735,6 +735,10 @@ static int parse_options (char * options, struct ext3_sb_info *sbi,
 		case Opt_commit:
 			if (match_int(&args[0], &option))
 				return 0;
+			if (option < 0)
+				return 0;
+			if (option == 0)
+				option = JBD_DEFAULT_MAX_COMMIT_AGE;
 			sbi->s_commit_interval = HZ * option;
 			break;
 		case Opt_data_journal:

fs/jbd/journal.c

@@ -636,7 +636,7 @@ static journal_t * journal_init_common (void)
 	spin_lock_init(&journal->j_list_lock);
 	spin_lock_init(&journal->j_state_lock);
 
-	journal->j_commit_interval = (HZ * 5);
+	journal->j_commit_interval = (HZ * JBD_DEFAULT_MAX_COMMIT_AGE);
 
 	/* The journal is marked for error until we succeed with recovery! */
 	journal->j_flags = JFS_ABORT;

include/linux/jbd.h

@@ -42,6 +42,11 @@
  */
 #undef JBD_PARANOID_IOFAIL
 
+/*
+ * The default maximum commit age, in seconds.
+ */
+#define JBD_DEFAULT_MAX_COMMIT_AGE 5
+
 #ifdef CONFIG_JBD_DEBUG
 /*
  * Define JBD_EXPENSIVE_CHECKING to enable more expensive internal