[RFC] libbpf: Allow to emit all dependent definitions

[Jiri Olsa <jolsa@xxxxxxxxxx>]

Currently the bpf dumper does not emit definitions
of pointers to structs. It only emits forward type
declarations.

Having 2 structs like:

   struct B {
     int b;
   };

   struct A {
     struct B *ptr;
   };

the call to btf_dump__dump_type(id = struct A) dumps:

   struct B;
   struct A {
     struct B *ptr;
   };

It'd ease up bpftrace code if we could dump definitions
of all dependent types, like:

   struct B {
     int b;
   };
   struct A {
     struct B *ptr;
   };

So we could dereference all the pointers easily, instead
of searching for each access member's type and dumping it
separately.

Adding struct btf_dump_opts::emit_all to do that.

Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 tools/lib/bpf/btf.h      |  1 +
 tools/lib/bpf/btf_dump.c | 14 ++++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 9cb44b4fbf60..2c0d3158efd4 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -113,6 +113,7 @@ struct btf_dump;
 
 struct btf_dump_opts {
 	void *ctx;
+	bool emit_all;
 };
 
 typedef void (*btf_dump_printf_fn_t)(void *ctx, const char *fmt, va_list args);
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 139812b46c7b..bab08f6428e7 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -132,6 +132,7 @@ struct btf_dump *btf_dump__new(const struct btf *btf,
 	d->btf_ext = btf_ext;
 	d->printf_fn = printf_fn;
 	d->opts.ctx = opts ? opts->ctx : NULL;
+	d->opts.emit_all = opts ? opts->emit_all : false;
 
 	d->type_names = hashmap__new(str_hash_fn, str_equal_fn, NULL);
 	if (IS_ERR(d->type_names)) {
@@ -612,7 +613,12 @@ static bool btf_dump_is_blacklisted(struct btf_dump *d, __u32 id)
 static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id)
 {
 	struct btf_dump_type_aux_state *tstate = &d->type_states[id];
-	bool top_level_def = cont_id == 0;
+	/*
+	 * Emit difinitions (instead of forward declarations) in case
+	 * we are top level id, or we are asked to emit all definitions
+	 * via options.
+	 */
+	bool emit_def = cont_id == 0 || d->opts.emit_all;
 	const struct btf_type *t;
 	__u16 kind;
 
@@ -668,7 +674,7 @@ static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id)
 		tstate->emit_state = EMITTED;
 		break;
 	case BTF_KIND_ENUM:
-		if (top_level_def) {
+		if (emit_def) {
 			btf_dump_emit_enum_def(d, id, t, 0);
 			btf_dump_printf(d, ";\n\n");
 		}
@@ -714,7 +720,7 @@ static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id)
 		 * members have necessary forward-declarations, where
 		 * applicable
 		 */
-		if (top_level_def || t->name_off == 0) {
+		if (emit_def || t->name_off == 0) {
 			const struct btf_member *m = btf_members(t);
 			__u16 vlen = btf_vlen(t);
 			int i, new_cont_id;
@@ -728,7 +734,7 @@ static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id)
 			tstate->fwd_emitted = 1;
 		}
 
-		if (top_level_def) {
+		if (emit_def) {
 			btf_dump_emit_struct_def(d, id, t, 0);
 			btf_dump_printf(d, ";\n\n");
 			tstate->emit_state = EMITTED;
-- 
2.21.0