selftests/bpf: test passing iterator to a kfunc

Define BPF iterator "getter" kfunc, which accepts iterator pointer as
one of the arguments. Make sure that argument passed doesn't have to be
the very first argument (unlike new-next-destroy combo).
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240808232230.2848712-4-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

@@ -141,13 +141,12 @@ bpf_testmod_test_mod_kfunc(int i)
 
 __bpf_kfunc int bpf_iter_testmod_seq_new(struct bpf_iter_testmod_seq *it, s64 value, int cnt)
 {
-	if (cnt < 0) {
-		it->cnt = 0;
+	it->cnt = cnt;
+
+	if (cnt < 0)
 		return -EINVAL;
-	}
 
 	it->value = value;
-	it->cnt = cnt;
 
 	return 0;
 }
@@ -162,6 +161,14 @@ __bpf_kfunc s64 *bpf_iter_testmod_seq_next(struct bpf_iter_testmod_seq* it)
 	return &it->value;
 }
 
+__bpf_kfunc s64 bpf_iter_testmod_seq_value(int val, struct bpf_iter_testmod_seq* it__iter)
+{
+	if (it__iter->cnt < 0)
+		return 0;
+
+	return val + it__iter->value;
+}
+
 __bpf_kfunc void bpf_iter_testmod_seq_destroy(struct bpf_iter_testmod_seq *it)
 {
 	it->cnt = 0;
@@ -531,6 +538,7 @@ BTF_KFUNCS_START(bpf_testmod_common_kfunc_ids)
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_iter_testmod_seq_value)
 BTF_ID_FLAGS(func, bpf_kfunc_common_test)
 BTF_ID_FLAGS(func, bpf_kfunc_dynptr_test)
 BTF_ID_FLAGS(func, bpf_testmod_ctx_create, KF_ACQUIRE | KF_RET_NULL)

tools/testing/selftests/bpf/progs/iters_testmod_seq.c

@@ -12,6 +12,7 @@ struct bpf_iter_testmod_seq {
 
 extern int bpf_iter_testmod_seq_new(struct bpf_iter_testmod_seq *it, s64 value, int cnt) __ksym;
 extern s64 *bpf_iter_testmod_seq_next(struct bpf_iter_testmod_seq *it) __ksym;
+extern s64 bpf_iter_testmod_seq_value(int blah, struct bpf_iter_testmod_seq *it) __ksym;
 extern void bpf_iter_testmod_seq_destroy(struct bpf_iter_testmod_seq *it) __ksym;
 
 const volatile __s64 exp_empty = 0 + 1;
@@ -76,4 +77,53 @@ int testmod_seq_truncated(const void *ctx)
 	return 0;
 }
 
+SEC("?raw_tp")
+__failure
+__msg("expected an initialized iter_testmod_seq as arg #2")
+int testmod_seq_getter_before_bad(const void *ctx)
+{
+	struct bpf_iter_testmod_seq it;
+
+	return bpf_iter_testmod_seq_value(0, &it);
+}
+
+SEC("?raw_tp")
+__failure
+__msg("expected an initialized iter_testmod_seq as arg #2")
+int testmod_seq_getter_after_bad(const void *ctx)
+{
+	struct bpf_iter_testmod_seq it;
+	s64 sum = 0, *v;
+
+	bpf_iter_testmod_seq_new(&it, 100, 100);
+
+	while ((v = bpf_iter_testmod_seq_next(&it))) {
+		sum += *v;
+	}
+
+	bpf_iter_testmod_seq_destroy(&it);
+
+	return sum + bpf_iter_testmod_seq_value(0, &it);
+}
+
+SEC("?socket")
+__success __retval(1000000)
+int testmod_seq_getter_good(const void *ctx)
+{
+	struct bpf_iter_testmod_seq it;
+	s64 sum = 0, *v;
+
+	bpf_iter_testmod_seq_new(&it, 100, 100);
+
+	while ((v = bpf_iter_testmod_seq_next(&it))) {
+		sum += *v;
+	}
+
+	sum *= bpf_iter_testmod_seq_value(0, &it);
+
+	bpf_iter_testmod_seq_destroy(&it);
+
+	return sum;
+}
+
 char _license[] SEC("license") = "GPL";