ext4: hook the ext3 migration interface to the EXT4_IOC_SETFLAGS ioctl

This patch hooks the ext3 to ext4 migrate interface to
EXT4_IOC_SETFLAGS ioctl. The userspace interface is via chattr +e.  We
only allow setting extent flags.  Clearing extent flag (migrating from
ext4 to ext3) is not supported.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -245,7 +245,7 @@ struct flex_groups {
 #define EXT4_RESERVED_FL		0x80000000 /* reserved for ext4 lib */
 
 #define EXT4_FL_USER_VISIBLE		0x000BDFFF /* User visible flags */
-#define EXT4_FL_USER_MODIFIABLE		0x000380FF /* User modifiable flags */
+#define EXT4_FL_USER_MODIFIABLE		0x000B80FF /* User modifiable flags */
 
 /*
  * Inode dynamic state flags

fs/ext4/ioctl.c

@@ -34,7 +34,7 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return put_user(flags, (int __user *) arg);
 	case EXT4_IOC_SETFLAGS: {
 		handle_t *handle = NULL;
-		int err;
+		int err, migrate = 0;
 		struct ext4_iloc iloc;
 		unsigned int oldflags;
 		unsigned int jflag;
@@ -82,6 +82,17 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			if (!capable(CAP_SYS_RESOURCE))
 				goto flags_out;
 		}
+		if (oldflags & EXT4_EXTENTS_FL) {
+			/* We don't support clearning extent flags */
+			if (!(flags & EXT4_EXTENTS_FL)) {
+				err = -EOPNOTSUPP;
+				goto flags_out;
+			}
+		} else if (flags & EXT4_EXTENTS_FL) {
+			/* migrate the file */
+			migrate = 1;
+			flags &= ~EXT4_EXTENTS_FL;
+		}
 
 		handle = ext4_journal_start(inode, 1);
 		if (IS_ERR(handle)) {
@@ -109,6 +120,10 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 		if ((jflag ^ oldflags) & (EXT4_JOURNAL_DATA_FL))
 			err = ext4_change_inode_journal_flag(inode, jflag);
+		if (err)
+			goto flags_out;
+		if (migrate)
+			err = ext4_ext_migrate(inode);
 flags_out:
 		mutex_unlock(&inode->i_mutex);
 		mnt_drop_write(filp->f_path.mnt);