bcachefs: create internal disk_groups sysfs file

We have bch2_sb_disk_groups_to_text() to dump disk group labels, but
no good information on device group membership at runtime. Add
bch2_disk_groups_to_text() and an associated 'disk_groups' sysfs
file to print group and device relationships.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/disk_groups.c

@@ -87,6 +87,40 @@ static int bch2_sb_disk_groups_validate(struct bch_sb *sb,
 	return ret;
 }
 
+void bch2_disk_groups_to_text(struct printbuf *out, struct bch_fs *c)
+{
+	struct bch_disk_groups_cpu *g;
+	struct bch_dev *ca;
+	int i;
+	unsigned iter;
+
+	out->atomic++;
+	rcu_read_lock();
+
+	g = rcu_dereference(c->disk_groups);
+	if (!g)
+		goto out;
+
+	for (i = 0; i < g->nr; i++) {
+		if (i)
+			prt_printf(out, " ");
+
+		if (g->entries[i].deleted) {
+			prt_printf(out, "[deleted]");
+			continue;
+		}
+
+		prt_printf(out, "[parent %d devs", g->entries[i].parent);
+		for_each_member_device_rcu(ca, c, iter, &g->entries[i].devs)
+			prt_printf(out, " %s", ca->name);
+		prt_printf(out, "]");
+	}
+
+out:
+	rcu_read_unlock();
+	out->atomic--;
+}
+
 static void bch2_sb_disk_groups_to_text(struct printbuf *out,
 					struct bch_sb *sb,
 					struct bch_sb_field *f)

fs/bcachefs/disk_groups.h

@@ -88,4 +88,6 @@ int bch2_dev_group_set(struct bch_fs *, struct bch_dev *, const char *);
 const char *bch2_sb_validate_disk_groups(struct bch_sb *,
 					 struct bch_sb_field *);
 
+void bch2_disk_groups_to_text(struct printbuf *, struct bch_fs *);
+
 #endif /* _BCACHEFS_DISK_GROUPS_H */

fs/bcachefs/sysfs.c

@@ -223,6 +223,7 @@ static void bch2_write_refs_to_text(struct printbuf *out, struct bch_fs *c)
 #endif
 
 read_attribute(internal_uuid);
+read_attribute(disk_groups);
 
 read_attribute(has_data);
 read_attribute(alloc_debug);
@@ -471,6 +472,9 @@ SHOW(bch2_fs)
 	if (attr == &sysfs_nocow_lock_table)
 		bch2_nocow_locks_to_text(out, &c->nocow_locks);
 
+	if (attr == &sysfs_disk_groups)
+		bch2_disk_groups_to_text(out, c);
+
 	return 0;
 }
 
@@ -681,6 +685,8 @@ struct attribute *bch2_fs_internal_files[] = {
 	&sysfs_moving_ctxts,
 
 	&sysfs_internal_uuid,
+
+	&sysfs_disk_groups,
 	NULL
 };