nilfs2: change default of 'errors' mount option to 'remount-ro' mode

Like ext3, nilfs has 'errors' mount option to allow specifying desired
behavior on severe errors.

Currently, the default action is 'errors=continue' and has potential
to advance filesystem corruption for severe errors.

This will change the action to 'errors=remount-ro' to avoid the issue.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

Documentation/filesystems/nilfs2.txt

@@ -50,8 +50,8 @@ NILFS2 supports the following mount options:
 (*) == default
 
 nobarrier		Disables barriers.
-errors=continue(*)	Keep going on a filesystem error.
-errors=remount-ro	Remount the filesystem read-only on an error.
+errors=continue		Keep going on a filesystem error.
+errors=remount-ro(*)	Remount the filesystem read-only on an error.
 errors=panic		Panic and halt the machine if an error occurs.
 cp=n			Specify the checkpoint-number of the snapshot to be
 			mounted.  Checkpoints and snapshots are listed by lscp

fs/nilfs2/super.c

@@ -470,10 +470,10 @@ static int nilfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (nilfs_test_opt(sbi, SNAPSHOT))
 		seq_printf(seq, ",cp=%llu",
 			   (unsigned long long int)sbi->s_snapshot_cno);
-	if (nilfs_test_opt(sbi, ERRORS_RO))
-		seq_printf(seq, ",errors=remount-ro");
 	if (nilfs_test_opt(sbi, ERRORS_PANIC))
 		seq_printf(seq, ",errors=panic");
+	if (nilfs_test_opt(sbi, ERRORS_CONT))
+		seq_printf(seq, ",errors=continue");
 	if (nilfs_test_opt(sbi, STRICT_ORDER))
 		seq_printf(seq, ",order=strict");
 	if (nilfs_test_opt(sbi, NORECOVERY))
@@ -631,7 +631,7 @@ nilfs_set_default_options(struct nilfs_sb_info *sbi,
 			  struct nilfs_super_block *sbp)
 {
 	sbi->s_mount_opt =
-		NILFS_MOUNT_ERRORS_CONT | NILFS_MOUNT_BARRIER;
+		NILFS_MOUNT_ERRORS_RO | NILFS_MOUNT_BARRIER;
 }
 
 static int nilfs_setup_super(struct nilfs_sb_info *sbi)