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

Showing the changes to tools/testing/selftests/bpf/test_cpp.cpp (1 of 1 file). Show all

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

@@ -5,18 +5,100 @@ · 4 unmodified lines
5	5	#include <bpf/btf.h>
6	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	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	94	int main(int argc, char *argv[])
15	95	{
16	96	struct btf_dump_opts opts = { };
17	97	struct test_core_extern *skel;
18	98	struct btf *btf;
19	99
	100	+ try_skeleton_template();
	101	+
20	102	/* libbpf.h */
21	103	libbpf_set_print(NULL);
22	104
@@ -25,7 +107,8 @@ int main(int argc, char *argv[]) · 2 unmodified lines
25	107
26	108	/* btf.h */
27	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	113	/* BPF skeleton */
31	114	skel = test_core_extern__open_and_load();