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selftests/bpf: Add Skeleton templated wrapper as an example
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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().

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220212055733.539056-3-andrii@kernel.org
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anakryiko authored and Alexei Starovoitov committed Feb 15, 2022
1 parent bb8ffe6 commit 189e0ec
Showing 1 changed file with 85 additions and 2 deletions.
87 changes: 85 additions & 2 deletions tools/testing/selftests/bpf/test_cpp.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -5,18 +5,100 @@
#include <bpf/btf.h>
#include "test_core_extern.skel.h"

/* do nothing, just make sure we can link successfully */
template <typename T>
class Skeleton {
private:
T *skel;
public:
Skeleton(): skel(nullptr) { }

~Skeleton() { if (skel) T::destroy(skel); }

int open(const struct bpf_object_open_opts *opts = nullptr)
{
int err;

if (skel)
return -EBUSY;

skel = T::open(opts);
err = libbpf_get_error(skel);
if (err) {
skel = nullptr;
return err;
}

return 0;
}

int load() { return T::load(skel); }

int attach() { return T::attach(skel); }

void detach() { return T::detach(skel); }

const T* operator->() const { return skel; }

T* operator->() { return skel; }

const T *get() const { return skel; }
};

static void dump_printf(void *ctx, const char *fmt, va_list args)
{
}

static void try_skeleton_template()
{
Skeleton<test_core_extern> skel;
std::string prog_name;
int err;
LIBBPF_OPTS(bpf_object_open_opts, opts);

err = skel.open(&opts);
if (err) {
fprintf(stderr, "Skeleton open failed: %d\n", err);
return;
}

skel->data->kern_ver = 123;
skel->data->int_val = skel->data->ushort_val;

err = skel.load();
if (err) {
fprintf(stderr, "Skeleton load failed: %d\n", err);
return;
}

if (!skel->kconfig->CONFIG_BPF_SYSCALL)
fprintf(stderr, "Seems like CONFIG_BPF_SYSCALL isn't set?!\n");

err = skel.attach();
if (err) {
fprintf(stderr, "Skeleton attach failed: %d\n", err);
return;
}

prog_name = bpf_program__name(skel->progs.handle_sys_enter);
if (prog_name != "handle_sys_enter")
fprintf(stderr, "Unexpected program name: %s\n", prog_name.c_str());

bpf_link__destroy(skel->links.handle_sys_enter);
skel->links.handle_sys_enter = bpf_program__attach(skel->progs.handle_sys_enter);

skel.detach();

/* destructor will destory underlying skeleton */
}

int main(int argc, char *argv[])
{
struct btf_dump_opts opts = { };
struct test_core_extern *skel;
struct btf *btf;

try_skeleton_template();

/* libbpf.h */
libbpf_set_print(NULL);

Expand All @@ -25,7 +107,8 @@ int main(int argc, char *argv[])

/* btf.h */
btf = btf__new(NULL, 0);
btf_dump__new(btf, dump_printf, nullptr, &opts);
if (!libbpf_get_error(btf))
btf_dump__new(btf, dump_printf, nullptr, &opts);

/* BPF skeleton */
skel = test_core_extern__open_and_load();
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