btrfs: Add datasum mount option.

Add datasum mount option to enable checksum with
remount option.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

Documentation/filesystems/btrfs.txt

@@ -159,8 +159,10 @@ Options with (*) are default options and will not show in the mount options.
 	Enable/disable data copy-on-write for newly created files.
 	Nodatacow implies nodatasum, and disables all compression.
 
+  datasum(*)
   nodatasum
-	Disable data checksumming for newly created files.
+	Enable/disable data checksumming for newly created files.
+	Datasum implies datacow.
 
   notreelog
 	Disable the tree logging used for fsync and O_SYNC writes.

fs/btrfs/super.c

@@ -325,6 +325,7 @@ enum {
 	Opt_check_integrity_print_mask, Opt_fatal_errors, Opt_rescan_uuid_tree,
 	Opt_commit_interval, Opt_barrier, Opt_nodefrag, Opt_nodiscard,
 	Opt_noenospc_debug, Opt_noflushoncommit, Opt_acl, Opt_datacow,
+	Opt_datasum,
 	Opt_err,
 };
 
@@ -334,6 +335,7 @@ static match_table_t tokens = {
 	{Opt_subvolid, "subvolid=%s"},
 	{Opt_device, "device=%s"},
 	{Opt_nodatasum, "nodatasum"},
+	{Opt_datasum, "datasum"},
 	{Opt_nodatacow, "nodatacow"},
 	{Opt_datacow, "datacow"},
 	{Opt_nobarrier, "nobarrier"},
@@ -434,6 +436,14 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 			btrfs_info(root->fs_info, "setting nodatasum");
 			btrfs_set_opt(info->mount_opt, NODATASUM);
 			break;
+		case Opt_datasum:
+			if (btrfs_test_opt(root, NODATACOW))
+				btrfs_info(root->fs_info, "setting datasum, datacow enabled");
+			else
+				btrfs_info(root->fs_info, "setting datasum");
+			btrfs_clear_opt(info->mount_opt, NODATACOW);
+			btrfs_clear_opt(info->mount_opt, NODATASUM);
+			break;
 		case Opt_nodatacow:
 			if (!btrfs_test_opt(root, COMPRESS) ||
 				!btrfs_test_opt(root, FORCE_COMPRESS)) {