selftests/bpf: Add Skeleton templated wrapper as an example

Add an example of how to build C++ template-based BPF skeleton wrapper. It's an actually runnable valid use of skeleton through more C++-like interface. Note that skeleton destuction happens implicitly through Skeleton<T>'s destructor. Also make test_cpp runnable as it would have crashed on invalid btf passed into btf_dump__new().

Andrii Nakryiko committed 4 years ago

Commit 189e0ec1 parent bb8ffe61 file · +85 −2Browse files

Unified · Split

tools/testing/selftests/bpf/test_cpp.cpp+85−2

@@ -5,18 +5,100 @@ · 4 unmodified lines
5	#include <bpf/btf.h>	5	#include <bpf/btf.h>
6	#include "test_core_extern.skel.h"	6	#include "test_core_extern.skel.h"
7		7
8	/* do nothing, just make sure we can link successfully */	8	template <typename T>
		9	class Skeleton {
		10	private:
		11	T *skel;
		12	public:
		13	Skeleton(): skel(nullptr) { }
		14
		15	~Skeleton() { if (skel) T::destroy(skel); }
		16
		17	int open(const struct bpf_object_open_opts *opts = nullptr)
		18	{
		19	int err;
		20
		21	if (skel)
		22	return -EBUSY;
		23
		24	skel = T::open(opts);
		25	err = libbpf_get_error(skel);
		26	if (err) {
		27	skel = nullptr;
		28	return err;
		29	}
		30
		31	return 0;
		32	}
		33
		34	int load() { return T::load(skel); }
		35
		36	int attach() { return T::attach(skel); }
		37
		38	void detach() { return T::detach(skel); }
		39
		40	const T* operator->() const { return skel; }
		41
		42	T* operator->() { return skel; }
		43
		44	const T *get() const { return skel; }
		45	};
9		46
10	static void dump_printf(void ctx, const char fmt, va_list args)	47	static void dump_printf(void ctx, const char fmt, va_list args)
11	{	48	{
12	}	49	}
13		50
		51	static void try_skeleton_template()
		52	{
		53	Skeleton<test_core_extern> skel;
		54	std::string prog_name;
		55	int err;
		56	LIBBPF_OPTS(bpf_object_open_opts, opts);
		57
		58	err = skel.open(&opts);
		59	if (err) {
		60	fprintf(stderr, "Skeleton open failed: %d\n", err);
		61	return;
		62	}
		63
		64	skel->data->kern_ver = 123;
		65	skel->data->int_val = skel->data->ushort_val;
		66
		67	err = skel.load();
		68	if (err) {
		69	fprintf(stderr, "Skeleton load failed: %d\n", err);
		70	return;
		71	}
		72
		73	if (!skel->kconfig->CONFIG_BPF_SYSCALL)
		74	fprintf(stderr, "Seems like CONFIG_BPF_SYSCALL isn't set?!\n");
		75
		76	err = skel.attach();
		77	if (err) {
		78	fprintf(stderr, "Skeleton attach failed: %d\n", err);
		79	return;
		80	}
		81
		82	prog_name = bpf_program__name(skel->progs.handle_sys_enter);
		83	if (prog_name != "handle_sys_enter")
		84	fprintf(stderr, "Unexpected program name: %s\n", prog_name.c_str());
		85
		86	bpf_link__destroy(skel->links.handle_sys_enter);
		87	skel->links.handle_sys_enter = bpf_program__attach(skel->progs.handle_sys_enter);
		88
		89	skel.detach();
		90
		91	/* destructor will destory underlying skeleton */
		92	}
		93
14	int main(int argc, char *argv[])	94	int main(int argc, char *argv[])
15	{	95	{
16	struct btf_dump_opts opts = { };	96	struct btf_dump_opts opts = { };
17	struct test_core_extern *skel;	97	struct test_core_extern *skel;
18	struct btf *btf;	98	struct btf *btf;
19		99
		100	try_skeleton_template();
		101
20	/* libbpf.h */	102	/* libbpf.h */
21	libbpf_set_print(NULL);	103	libbpf_set_print(NULL);
22		104
@@ -25,7 +107,8 @@ int main(int argc, char *argv[]) · 2 unmodified lines
25		107
26	/* btf.h */	108	/* btf.h */
27	btf = btf__new(NULL, 0);	109	btf = btf__new(NULL, 0);
28	btf_dump__new(btf, dump_printf, nullptr, &opts);	110	if (!libbpf_get_error(btf))
		111	btf_dump__new(btf, dump_printf, nullptr, &opts);
29		112
30	/* BPF skeleton */	113	/* BPF skeleton */
31	skel = test_core_extern__open_and_load();	114	skel = test_core_extern__open_and_load();