Index: linux-stage/fs/ext4/ext4.h
===================================================================
--- linux-stage.orig/fs/ext4/ext4.h	2011-03-14 15:57:13.613674482 +0800
+++ linux-stage/fs/ext4/ext4.h	2011-03-14 15:57:22.031906980 +0800
@@ -780,6 +780,7 @@
 #define EXT4_MOUNT_QUOTA		0x80000 /* Some quota option set */
 #define EXT4_MOUNT_USRQUOTA		0x100000 /* "old" user quota */
 #define EXT4_MOUNT_GRPQUOTA		0x200000 /* "old" group quota */
+#define EXT4_MOUNT_EXTENTS		0x400000 /* Extents support */
 #define EXT4_MOUNT_JOURNAL_CHECKSUM	0x800000 /* Journal checksums */
 #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT	0x1000000 /* Journal Async Commit */
 #define EXT4_MOUNT_I_VERSION            0x2000000 /* i_version support */
Index: linux-stage/fs/ext4/ext4_jbd2.h
===================================================================
--- linux-stage.orig/fs/ext4/ext4_jbd2.h	2011-03-14 15:57:12.000000000 +0800
+++ linux-stage/fs/ext4/ext4_jbd2.h	2011-03-14 15:58:55.957499110 +0800
@@ -33,7 +33,7 @@
 
 #define EXT4_SINGLEDATA_TRANS_BLOCKS(sb)				\
 	(EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_EXTENTS)   \
-	 ? 27U : 8U)
+	 || test_opt(sb, EXTENTS) ? 27U : 8U)
 
 #define ext4_journal_dirty_metadata(handle, bh)  \
                 ext4_handle_dirty_metadata(handle, NULL, bh)
Index: linux-stage/fs/ext4/extents.c
===================================================================
--- linux-stage.orig/fs/ext4/extents.c	2011-03-14 15:57:12.000000000 +0800
+++ linux-stage/fs/ext4/extents.c	2011-03-14 16:14:14.246265207 +0800
@@ -2553,7 +2553,7 @@
 	 * possible initialization would be here
 	 */
 
-	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_EXTENTS)) {
+	if (test_opt(sb, EXTENTS)) {
 #if defined(AGGRESSIVE_TEST) || defined(CHECK_BINSEARCH) || defined(EXTENTS_STATS)
 		printk(KERN_INFO "EXT4-fs: file extents enabled");
 #ifdef AGGRESSIVE_TEST
@@ -2580,7 +2580,7 @@
  */
 void ext4_ext_release(struct super_block *sb)
 {
-	if (!EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_EXTENTS))
+	if (!test_opt(sb, EXTENTS))
 		return;
 
 #ifdef EXTENTS_STATS
Index: linux-stage/fs/ext4/ialloc.c
===================================================================
--- linux-stage.orig/fs/ext4/ialloc.c	2011-03-14 15:57:13.000000000 +0800
+++ linux-stage/fs/ext4/ialloc.c	2011-03-14 16:02:03.334308846 +0800
@@ -1049,7 +1049,7 @@
 	if (err)
 		goto fail_free_drop;
 
-	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_EXTENTS)) {
+	if (test_opt(sb, EXTENTS)) {
 		/* set extent flag only for directory, file and normal symlink*/
 		if (S_ISDIR(mode) || S_ISREG(mode) || S_ISLNK(mode)) {
 			EXT4_I(inode)->i_flags |= EXT4_EXTENTS_FL;
Index: linux-stage/fs/ext4/migrate.c
===================================================================
--- linux-stage.orig/fs/ext4/migrate.c	2011-03-14 15:36:15.000000000 +0800
+++ linux-stage/fs/ext4/migrate.c	2011-03-14 16:05:39.083369164 +0800
@@ -459,13 +459,13 @@
 	unsigned long max_entries;
 	__u32 goal;
 
-	/*
-	 * If the filesystem does not support extents, or the inode
-	 * already is extent-based, error out.
-	 */
-	if (!EXT4_HAS_INCOMPAT_FEATURE(inode->i_sb,
-				       EXT4_FEATURE_INCOMPAT_EXTENTS) ||
-	    (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
+	if (!test_opt(inode->i_sb, EXTENTS))
+		/*
+		 * if mounted with noextents we don't allow the migrate
+		 */
+		return -EINVAL;
+
+	if ((EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
 		return -EINVAL;
 
 	if (S_ISLNK(inode->i_mode) && inode->i_blocks == 0)
Index: linux-stage/fs/ext4/super.c
===================================================================
--- linux-stage.orig/fs/ext4/super.c	2011-03-14 15:57:18.000000000 +0800
+++ linux-stage/fs/ext4/super.c	2011-03-14 16:11:58.234626200 +0800
@@ -942,6 +942,8 @@
 		seq_puts(seq, ",journal_async_commit");
 	if (test_opt(sb, NOBH))
 		seq_puts(seq, ",nobh");
+	if (!test_opt(sb, EXTENTS))
+		seq_puts(seq, ",noextents");
 	if (test_opt(sb, I_VERSION))
 		seq_puts(seq, ",i_version");
 	if (!test_opt(sb, DELALLOC))
@@ -1500,6 +1502,7 @@
 	Opt_inode_readahead_blks, Opt_journal_ioprio,
 	Opt_discard, Opt_nodiscard,
 	Opt_mballoc, Opt_bigendian_extents, Opt_force_over_16tb,
+	Opt_extents, Opt_noextents,
 };
 
 static const match_table_t tokens = {
@@ -1571,6 +1574,8 @@
 	{Opt_mballoc, "mballoc"},
 	{Opt_discard, "discard"},
 	{Opt_nodiscard, "nodiscard"},
+	{Opt_extents, "extents"},
+	{Opt_noextents, "noextents"},
 	{Opt_err, NULL},
 };
 
@@ -1613,6 +1618,7 @@
 	int qtype, qfmt;
 	char *qname;
 #endif
+	ext4_fsblk_t last_block;
 
 	if (!options)
 		return 1;
@@ -2017,6 +2023,32 @@
 		case Opt_force_over_16tb:
 			force_over_16tb = 1;
 			break;
+		case Opt_extents:
+			if (!EXT4_HAS_INCOMPAT_FEATURE(sb,
+					EXT4_FEATURE_INCOMPAT_EXTENTS)) {
+				ext4_warning(sb, "extents feature not enabled "
+						 "on this filesystem, use tune2fs");
+				return 0;
+			}
+			set_opt(sbi->s_mount_opt, EXTENTS);
+			break;
+		case Opt_noextents:
+			/*
+			 * When e2fsprogs support resizing an already existing
+			 * ext4 file system to greater than 2**32 we need to
+			 * add support to block allocator to handle growing
+			 * already existing block  mapped inode so that blocks
+			 * allocated for them fall within 2**32
+			 */
+			last_block = ext4_blocks_count(sbi->s_es) - 1;
+			if (last_block  > 0xffffffffULL) {
+				printk(KERN_ERR "EXT4-fs: Filesystem too "
+						"large to mount with "
+						"-o noextents options\n");
+				return 0;
+			}
+			clear_opt(sbi->s_mount_opt, EXTENTS);
+			break;
 		default:
 			ext4_msg(sb, KERN_ERR,
 			       "Unrecognized mount option \"%s\" "
@@ -2879,6 +2911,17 @@
 	set_opt(sbi->s_mount_opt, BARRIER);
 
 	/*
+	 * turn on extents feature by default in ext4 filesystem
+	 * only if feature flag already set by mkfs or tune2fs.
+	 * Use -o noextents to turn it off
+	 */
+	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_EXTENTS))
+		set_opt(sbi->s_mount_opt, EXTENTS);
+	else
+		ext4_warning(sb, "extents feature not enabled on this filesystem, "
+				 "use tune2fs.");
+
+	/*
 	 * enable delayed allocation by default
 	 * Use -o nodelalloc to turn it off
 	 */