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().

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

diff --git a/tools/testing/selftests/bpf/test_cpp.cpp b/tools/testing/selftests/bpf/test_cpp.cpp
index e00201de28901254cf508108317a4dfd5fcbcac1..773f165c4898e9062b9580f8158e1cc909c7ad4f 100644 (file)
--- a/tools/testing/selftests/bpf/test_cpp.cpp
+++ b/tools/testing/selftests/bpf/test_cpp.cpp
@@ -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);
 
@@ -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();