Re: barriers off by default?

[Theodore Tso <tytso@mit.edu>]

Given the discussion on the other thread about the performance impact
and hard-to-hit nature of barrier problems, how about this?

    		       	  	  	    	- Ted

ext4: Add EXT4_DEFM_BARRIER and EXT4_DEFM_I_VERSION default mount options

Allow the i_version and barrier mount options to be set by default via
flags in the ext4 superblock.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index b7ffb91..afeba1f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -785,6 +785,8 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 #define EXT4_DEFM_JMODE_DATA	0x0020
 #define EXT4_DEFM_JMODE_ORDERED	0x0040
 #define EXT4_DEFM_JMODE_WBACK	0x0060
+#define EXT4_DEFM_BARRIER	0x0080
+#define EXT4_DEFM_I_VERSION	0x0100
 
 /*
  * Structure of a directory entry
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 09d9359..c0a657c 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -729,7 +729,7 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 		seq_printf(seq, ",commit=%u",
 			   (unsigned) (sbi->s_commit_interval / HZ));
 	}
-	if (test_opt(sb, BARRIER))
+	if (test_opt(sb, BARRIER) && !(def_mount_opts & EXT4_DEFM_BARRIER))
 		seq_puts(seq, ",barrier=1");
 	if (test_opt(sb, NOBH))
 		seq_puts(seq, ",nobh");
@@ -737,7 +737,7 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 		seq_puts(seq, ",noextents");
 	if (!test_opt(sb, MBALLOC))
 		seq_puts(seq, ",nomballoc");
-	if (test_opt(sb, I_VERSION))
+	if (test_opt(sb, I_VERSION) && !(def_mount_opts & EXT4_DEFM_I_VERSION))
 		seq_puts(seq, ",i_version");
 
 	if (sbi->s_stripe)
@@ -1896,6 +1896,12 @@ static int ext4_fill_super (struct super_block *sb, void *data, int silent)
 	else if ((def_mount_opts & EXT4_DEFM_JMODE) == EXT4_DEFM_JMODE_WBACK)
 		sbi->s_mount_opt |= EXT4_MOUNT_WRITEBACK_DATA;
 
+	if (def_mount_opts & EXT4_DEFM_BARRIER)
+		set_opt(sbi->s_mount_opt, BARRIER);
+
+	if (def_mount_opts & EXT4_DEFM_I_VERSION)
+		sb->s_flags |= MS_I_VERSION;
+
 	if (le16_to_cpu(sbi->s_es->s_errors) == EXT4_ERRORS_PANIC)
 		set_opt(sbi->s_mount_opt, ERRORS_PANIC);
 	else if (le16_to_cpu(sbi->s_es->s_errors) == EXT4_ERRORS_CONTINUE)