ext4: elevate write count for migrate ioctl

The migrate ioctl writes to the filsystem, so we need to elevate the
write count.

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

@@ -1084,8 +1084,7 @@ extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
 extern long ext4_compat_ioctl(struct file *, unsigned int, unsigned long);
 
 /* migrate.c */
-extern int ext4_ext_migrate(struct inode *, struct file *, unsigned int,
+extern int ext4_ext_migrate(struct inode *);
-		       unsigned long);
 /* namei.c */
 extern int ext4_orphan_add(handle_t *, struct inode *);
 extern int ext4_orphan_del(handle_t *, struct inode *);

fs/ext4/ioctl.c

@@ -267,7 +267,26 @@ setversion_out:
 	}
 
 	case EXT4_IOC_MIGRATE:
-		return ext4_ext_migrate(inode, filp, cmd, arg);
+	{
+		int err;
+		if (!is_owner_or_cap(inode))
+			return -EACCES;
+
+		err = mnt_want_write(filp->f_path.mnt);
+		if (err)
+			return err;
+		/*
+		 * inode_mutex prevent write and truncate on the file.
+		 * Read still goes through. We take i_data_sem in
+		 * ext4_ext_swap_inode_data before we switch the
+		 * inode format to prevent read.
+		 */
+		mutex_lock(&(inode->i_mutex));
+		err = ext4_ext_migrate(inode);
+		mutex_unlock(&(inode->i_mutex));
+		mnt_drop_write(filp->f_path.mnt);
+		return err;
+	}
 
 	default:
 		return -ENOTTY;

fs/ext4/migrate.c

@@ -447,8 +447,7 @@ static int free_ext_block(handle_t *handle, struct inode *inode)
 
 }
 
-int ext4_ext_migrate(struct inode *inode, struct file *filp,
+int ext4_ext_migrate(struct inode *inode)
-				unsigned int cmd, unsigned long arg)
 {
 	handle_t *handle;
 	int retval = 0, i;
@@ -515,12 +514,6 @@ int ext4_ext_migrate(struct inode *inode, struct file *filp,
 	 * trascation that created the inode. Later as and
 	 * when we add extents we extent the journal
 	 */
-	/*
-	 * inode_mutex prevent write and truncate on the file. Read still goes
-	 * through. We take i_data_sem in ext4_ext_swap_inode_data before we
-	 * switch the inode format to prevent read.
-	 */
-	mutex_lock(&(inode->i_mutex));
 	/*
 	 * Even though we take i_mutex we can still cause block allocation
 	 * via mmap write to holes. If we have allocated new blocks we fail
@@ -623,7 +616,6 @@ err_out:
 	tmp_inode->i_nlink = 0;
 
 	ext4_journal_stop(handle);
-	mutex_unlock(&(inode->i_mutex));
 
 	if (tmp_inode)
 		iput(tmp_inode);