bpf: Create links for BPF struct_ops maps.

Make bpf_link support struct_ops.  Previously, struct_ops were always
used alone without any associated links. Upon updating its value, a
struct_ops would be activated automatically. Yet other BPF program
types required to make a bpf_link with their instances before they
could become active. Now, however, you can create an inactive
struct_ops, and create a link to activate it later.

With bpf_links, struct_ops has a behavior similar to other BPF program
types. You can pin/unpin them from their links and the struct_ops will
be deactivated when its link is removed while previously need someone
to delete the value for it to be deactivated.

bpf_links are responsible for registering their associated
struct_ops. You can only use a struct_ops that has the BPF_F_LINK flag
set to create a bpf_link, while a structs without this flag behaves in
the same manner as before and is registered upon updating its value.

The BPF_LINK_TYPE_STRUCT_OPS serves a dual purpose. Not only is it
used to craft the links for BPF struct_ops programs, but also to
create links for BPF struct_ops them-self.  Since the links of BPF
struct_ops programs are only used to create trampolines internally,
they are never seen in other contexts. Thus, they can be reused for
struct_ops themself.

To maintain a reference to the map supporting this link, we add
bpf_struct_ops_link as an additional type. The pointer of the map is
RCU and won't be necessary until later in the patchset.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
Link: https://lore.kernel.org/r/20230323032405.3735486-4-kuifeng@meta.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f04098468d7a..8552279efe46 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1518,6 +1518,7 @@ struct bpf_struct_ops {
 			   void *kdata, const void *udata);
 	int (*reg)(void *kdata);
 	void (*unreg)(void *kdata);
+	int (*validate)(void *kdata);
 	const struct btf_type *type;
 	const struct btf_type *value_type;
 	const char *name;
@@ -1552,6 +1553,7 @@ static inline void bpf_module_put(const void *data, struct module *owner)
 	else
 		module_put(owner);
 }
+int bpf_struct_ops_link_create(union bpf_attr *attr);
 
 #ifdef CONFIG_NET
 /* Define it here to avoid the use of forward declaration */
@@ -1592,6 +1594,11 @@ static inline int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map,
 {
 	return -EINVAL;
 }
+static inline int bpf_struct_ops_link_create(union bpf_attr *attr)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif
 
 #if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_LSM)