bpf: add struct_ops_tab to btf.

Maintain a registry of registered struct_ops types in the per-btf (module)
struct_ops_tab. This registry allows for easy lookup of struct_ops types
that are registered by a specific module.

It is a preparation work for supporting kernel module struct_ops in a
latter patch. Each struct_ops will be registered under its own kernel
module btf and will be stored in the newly added btf->struct_ops_tab. The
bpf verifier and bpf syscall (e.g. prog and map cmd) can find the
struct_ops and its btf type/size/id... information from
btf->struct_ops_tab.
Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Link: https://lore.kernel.org/r/20240119225005.668602-5-thinker.li@gmail.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

kernel/bpf/btf.c

@@ -241,6 +241,12 @@ struct btf_id_dtor_kfunc_tab {
 	struct btf_id_dtor_kfunc dtors[];
 };
 
+struct btf_struct_ops_tab {
+	u32 cnt;
+	u32 capacity;
+	struct bpf_struct_ops_desc ops[];
+};
+
 struct btf {
 	void *data;
 	struct btf_type **types;
@@ -258,6 +264,7 @@ struct btf {
 	struct btf_kfunc_set_tab *kfunc_set_tab;
 	struct btf_id_dtor_kfunc_tab *dtor_kfunc_tab;
 	struct btf_struct_metas *struct_meta_tab;
+	struct btf_struct_ops_tab *struct_ops_tab;
 
 	/* split BTF support */
 	struct btf *base_btf;
@@ -1688,11 +1695,20 @@ static void btf_free_struct_meta_tab(struct btf *btf)
 	btf->struct_meta_tab = NULL;
 }
 
+static void btf_free_struct_ops_tab(struct btf *btf)
+{
+	struct btf_struct_ops_tab *tab = btf->struct_ops_tab;
+
+	kfree(tab);
+	btf->struct_ops_tab = NULL;
+}
+
 static void btf_free(struct btf *btf)
 {
 	btf_free_struct_meta_tab(btf);
 	btf_free_dtor_kfunc_tab(btf);
 	btf_free_kfunc_set_tab(btf);
+	btf_free_struct_ops_tab(btf);
 	kvfree(btf->types);
 	kvfree(btf->resolved_sizes);
 	kvfree(btf->resolved_ids);
@@ -8689,3 +8705,42 @@ bool btf_type_ids_nocast_alias(struct bpf_verifier_log *log,
 
 	return !strncmp(reg_name, arg_name, cmp_len);
 }
+
+static int
+btf_add_struct_ops(struct btf *btf, struct bpf_struct_ops *st_ops)
+{
+	struct btf_struct_ops_tab *tab, *new_tab;
+	int i;
+
+	tab = btf->struct_ops_tab;
+	if (!tab) {
+		tab = kzalloc(offsetof(struct btf_struct_ops_tab, ops[4]),
+			      GFP_KERNEL);
+		if (!tab)
+			return -ENOMEM;
+		tab->capacity = 4;
+		btf->struct_ops_tab = tab;
+	}
+
+	for (i = 0; i < tab->cnt; i++)
+		if (tab->ops[i].st_ops == st_ops)
+			return -EEXIST;
+
+	if (tab->cnt == tab->capacity) {
+		new_tab = krealloc(tab,
+				   offsetof(struct btf_struct_ops_tab,
+					    ops[tab->capacity * 2]),
+				   GFP_KERNEL);
+		if (!new_tab)
+			return -ENOMEM;
+		tab = new_tab;
+		tab->capacity *= 2;
+		btf->struct_ops_tab = tab;
+	}
+
+	tab->ops[btf->struct_ops_tab->cnt].st_ops = st_ops;
+
+	btf->struct_ops_tab->cnt++;
+
+	return 0;
+}