+static ssize_t btrfs_feature_attr_store(struct kobject *kobj,
+ struct kobj_attribute *a,
+ const char *buf, size_t count)
+{
+ struct btrfs_fs_info *fs_info;
+ struct btrfs_feature_attr *fa = to_btrfs_feature_attr(a);
+ struct btrfs_trans_handle *trans;
+ u64 features, set, clear;
+ unsigned long val;
+ int ret;
+
+ fs_info = to_fs_info(kobj);
+ if (!fs_info)
+ return -EPERM;
+
+ ret = kstrtoul(skip_spaces(buf), 0, &val);
+ if (ret)
+ return ret;
+
+ if (fa->feature_set == FEAT_COMPAT) {
+ set = BTRFS_FEATURE_COMPAT_SAFE_SET;
+ clear = BTRFS_FEATURE_COMPAT_SAFE_CLEAR;
+ } else if (fa->feature_set == FEAT_COMPAT_RO) {
+ set = BTRFS_FEATURE_COMPAT_RO_SAFE_SET;
+ clear = BTRFS_FEATURE_COMPAT_RO_SAFE_CLEAR;
+ } else {
+ set = BTRFS_FEATURE_INCOMPAT_SAFE_SET;
+ clear = BTRFS_FEATURE_INCOMPAT_SAFE_CLEAR;
+ }
+
+ features = get_features(fs_info, fa->feature_set);
+
+ /* Nothing to do */
+ if ((val && (features & fa->feature_bit)) ||
+ (!val && !(features & fa->feature_bit)))
+ return count;
+
+ if ((val && !(set & fa->feature_bit)) ||
+ (!val && !(clear & fa->feature_bit))) {
+ btrfs_info(fs_info,
+ "%sabling feature %s on mounted fs is not supported.",
+ val ? "En" : "Dis", fa->kobj_attr.attr.name);
+ return -EPERM;
+ }
+
+ btrfs_info(fs_info, "%s %s feature flag",
+ val ? "Setting" : "Clearing", fa->kobj_attr.attr.name);
+
+ trans = btrfs_start_transaction(fs_info->fs_root, 1);
+ if (IS_ERR(trans))
+ return PTR_ERR(trans);
+
+ spin_lock(&fs_info->super_lock);
+ features = get_features(fs_info, fa->feature_set);
+ if (val)
+ features |= fa->feature_bit;
+ else
+ features &= ~fa->feature_bit;
+ set_features(fs_info, fa->feature_set, features);
+ spin_unlock(&fs_info->super_lock);
+
+ ret = btrfs_commit_transaction(trans, fs_info->fs_root);
+ if (ret)
+ return ret;
+
+ return count;
+}
+