在 2025/2/8 06:35, Eduard Zingerman 写道:
On Thu, 2025-02-06 at 13:15 +0800, Tao Chen wrote:
[...]
LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type,
enum bpf_func_id helper_id, const void *opts);
-
+/**
+ * @brief **libbpf_probe_bpf_kfunc()** detects if host kernel supports the
+ * use of a given BPF kfunc from specified BPF program type.
+ * @param prog_type BPF program type used to check the support of BPF kfunc
+ * @param kfunc_id The btf ID of BPF kfunc to check support for
+ * @param btf_fd The module BTF FD, if kfunc is defined in kernel module,
+ * btf_fd is used to point to module's BTF, 0 means kfunc defined in vmlinux.
Regarding '0' as special value:
in general FD is considered invalid only if it's negative, 0 is a valid FD.
Andrii, I remember there was a lengthy discussion about FD==0 and BPF,
but I don't remember the conclusion.
+ * @param opts reserved for future extensibility, should be NULL
+ * @return 1, if given combination of program type and kfunc is supported; 0,
+ * if the combination is not supported; negative error code if feature
+ * detection for provided input arguments failed or can't be performed
+ *
+ * Make sure the process has required set of CAP_* permissions (or runs as
+ * root) when performing feature checking.
+ */
+LIBBPF_API int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type,
+ int kfunc_id, int btf_fd, const void *opts);
/**
* @brief **libbpf_num_possible_cpus()** is a helper function to get the
* number of possible CPUs that the host kernel supports and expects.
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index a8b2936a1646..e93fae101efd 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -436,4 +436,5 @@ LIBBPF_1.6.0 {
bpf_linker__add_buf;
bpf_linker__add_fd;
bpf_linker__new_fd;
+ libbpf_probe_bpf_kfunc;
This is now in conflict with bpf-next.
My bad, i will rebase the repo.
} LIBBPF_1.5.0;
diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index e142130cb83c..c7f2b2dfbcf1 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -433,6 +433,61 @@ static bool can_probe_prog_type(enum bpf_prog_type prog_type)
return true;
}
+int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, int btf_fd,
+ const void *opts)
+{
+ struct bpf_insn insns[] = {
+ BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, btf_fd, kfunc_id),
+ BPF_EXIT_INSN(),
+ };
+ const size_t insn_cnt = ARRAY_SIZE(insns);
+ char buf[4096];
+ int *fd_array = NULL;
+ size_t fd_array_cnt = 0, fd_array_cap = fd_array_cnt;
+ int ret;
+
+ if (opts)
+ return libbpf_err(-EINVAL);
+
+ if (!can_probe_prog_type(prog_type))
+ return -EOPNOTSUPP;
+
+ if (btf_fd) {
+ ret = libbpf_ensure_mem((void **)&fd_array, &fd_array_cap,
+ sizeof(int), fd_array_cnt + btf_fd);
Please take a look at the tools/testing/selftests/bpf/prog_tests/fd_array.c,
e.g. test case check_fd_array_cnt__fd_array_ok(). The offset field of the
call instruction does not have to be an fd (as it only has 16 bits),
instead it's an offset inside the fd_array.
Here it would be sufficient to allocate a small array on stack.
Good idea，thanks for your guidance，I'll make the modifications in the
next version.
+ if (ret)
+ return ret;
+
+ /* In kernel, obtain the btf fd by means of the offset of
+ * the fd_array, and the offset is the btf fd.
+ */
+ fd_array[btf_fd] = btf_fd;
+ }
[...]
--
Best Regards
Dylane Chen
