From: Nikolay Borisov <nborisov@suse.com>
Date: Mon, 19 Nov 2018 17:37:45 +0200
Subject: btrfs: Add sysfs support for metadata_uuid feature
Patch-mainline: Submitted, awaiting review
References: fate#325871

Since the metadata_uuid is a new incompat feature it requires the
respective sysfs hooks. This patch adds the 'metdata_uuid' feature to
be shown if it supported by the kernel. Additionally it adds
/sys/fs/btrfs/UUID/metadata_uuid attribute which allows one to read
the current metadata_uuid.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/sysfs.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -205,6 +205,7 @@ BTRFS_FEAT_ATTR_INCOMPAT(extended_iref,
 BTRFS_FEAT_ATTR_INCOMPAT(raid56, RAID56);
 BTRFS_FEAT_ATTR_INCOMPAT(skinny_metadata, SKINNY_METADATA);
 BTRFS_FEAT_ATTR_INCOMPAT(no_holes, NO_HOLES);
+BTRFS_FEAT_ATTR_INCOMPAT(metadata_uuid, METADATA_UUID);
 BTRFS_FEAT_ATTR_COMPAT_RO(free_space_tree, FREE_SPACE_TREE);
 
 static struct attribute *btrfs_supported_feature_attrs[] = {
@@ -217,6 +218,7 @@ static struct attribute *btrfs_supported
 	BTRFS_FEAT_ATTR_PTR(raid56),
 	BTRFS_FEAT_ATTR_PTR(skinny_metadata),
 	BTRFS_FEAT_ATTR_PTR(no_holes),
+	BTRFS_FEAT_ATTR_PTR(metadata_uuid),
 	BTRFS_FEAT_ATTR_PTR(free_space_tree),
 	NULL
 };
@@ -448,11 +450,23 @@ static ssize_t btrfs_clone_alignment_sho
 
 BTRFS_ATTR(, clone_alignment, btrfs_clone_alignment_show);
 
+static ssize_t btrfs_metadata_uuid_show(struct kobject *kobj,
+				struct kobj_attribute *a, char *buf)
+{
+	struct btrfs_fs_info *fs_info = to_fs_info(kobj);
+
+	return snprintf(buf, PAGE_SIZE, "%pU\n",
+			fs_info->fs_devices->metadata_uuid);
+}
+
+BTRFS_ATTR(, metadata_uuid, btrfs_metadata_uuid_show);
+
 static const struct attribute *btrfs_attrs[] = {
 	BTRFS_ATTR_PTR(, label),
 	BTRFS_ATTR_PTR(, nodesize),
 	BTRFS_ATTR_PTR(, sectorsize),
 	BTRFS_ATTR_PTR(, clone_alignment),
+	BTRFS_ATTR_PTR(, metadata_uuid),
 	NULL,
 };