[PATCH bpf-next 4/6] bpf: detach a bpf_struct_ops_map from a link.

[Kui-Feng Lee <thinker.li@gmail.com>]

Allow user space programs to detach a struct_ops map from the attached
link.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 kernel/bpf/bpf_struct_ops.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 8e79b02a1ccb..4a8a7e5ffc56 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -1252,8 +1252,36 @@ static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map
 	return err;
 }
 
+static int bpf_struct_ops_map_link_detach(struct bpf_link *link)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_struct_ops_map *st_map;
+	struct bpf_map *map;
+
+	mutex_lock(&update_mutex);
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	map = rcu_dereference_protected(st_link->map, lockdep_is_held(&update_mutex));
+	if (!map) {
+		mutex_unlock(&update_mutex);
+		return -ENOENT;
+	}
+	st_map = container_of(map, struct bpf_struct_ops_map, map);
+
+	st_map->st_ops_desc->st_ops->unreg(&st_map->kvalue.data);
+
+	map_attached_null(st_map);
+	rcu_assign_pointer(st_link->map, NULL);
+	bpf_map_put(map);
+
+	mutex_unlock(&update_mutex);
+
+	return 0;
+}
+
 static const struct bpf_link_ops bpf_struct_ops_map_lops = {
 	.dealloc = bpf_struct_ops_map_link_dealloc,
+	.detach = bpf_struct_ops_map_link_detach,
 	.show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
 	.fill_link_info = bpf_struct_ops_map_link_fill_link_info,
 	.update_map = bpf_struct_ops_map_link_update,
-- 
2.34.1