Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
used to test the availability of the different eBPF kfuncs on the
current system.
Cc: Tao Chen <dylane.chen@didiglobal.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
tools/lib/bpf/libbpf.h | 19 ++++++++++++-
tools/lib/bpf/libbpf.map | 1 +
tools/lib/bpf/libbpf_probes.c | 51 +++++++++++++++++++++++++++++++++++
3 files changed, 70 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 3020ee45303a..c79b4475b956 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1680,7 +1680,24 @@ LIBBPF_API int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void
*/
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, which is >= 0, and < 0 means kfunc
+ * defined in vmlinux.
+ * @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 b5a838de6f47..3bbfe13aeb6a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -438,4 +438,5 @@ LIBBPF_1.6.0 {
bpf_linker__new_fd;
btf__add_decl_attr;
btf__add_type_attr;
+ libbpf_probe_bpf_kfunc;
} LIBBPF_1.5.0;
diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index de2b1205b436..8efebc18a215 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -431,6 +431,57 @@ 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, 1, kfunc_id),
+ BPF_EXIT_INSN(),
+ };
+ const size_t insn_cnt = ARRAY_SIZE(insns);
+ char buf[4096];
+ int fd_array[2] = {-1};
+ int ret;
+
+ if (opts)
+ return libbpf_err(-EINVAL);
+
+ if (!can_probe_prog_type(prog_type))
+ return libbpf_err(-EOPNOTSUPP);
+
+ if (btf_fd >= 0)
+ fd_array[1] = btf_fd;
+ else
+ /* insn.off = 0, means vmlinux btf */
+ insns[0].off = 0;
+
+ buf[0] = '\0';
+ ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
+ buf, sizeof(buf));
+ if (ret < 0)
+ return libbpf_err(ret);
+
+ if (ret > 0)
+ return 1; /* assume supported */
+
+ /* If BPF verifier recognizes BPF kfunc but it's not supported for
+ * given BPF program type, it will emit "calling kernel function
+ * <name> is not allowed". If the kfunc id is invalid,
+ * it will emit "kernel btf_id <id> is not a function". If BTF fd
+ * invalid in module BTF, it will emit "invalid module BTF fd specified" or
+ * "negative offset disallowed for kernel module function call". If
+ * kfunc prog not dev buound, it will emit "metadata kfuncs require
+ * device-bound program".
+ */
+ if (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
+ strstr(buf, "invalid module BTF fd") ||
+ strstr(buf, "negative offset disallowed") ||
+ strstr(buf, "device-bound program"))
+ return 0;
+
+ return 1;
+}
+
int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
const void *opts)
{
--
2.43.0On Mon, Feb 24, 2025 at 9:02 AM Tao Chen <chen.dylane@linux.dev> wrote:
>
> Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
> used to test the availability of the different eBPF kfuncs on the
> current system.
>
> Cc: Tao Chen <dylane.chen@didiglobal.com>
> Reviewed-by: Jiri Olsa <jolsa@kernel.org>
> Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
> ---
> tools/lib/bpf/libbpf.h | 19 ++++++++++++-
> tools/lib/bpf/libbpf.map | 1 +
> tools/lib/bpf/libbpf_probes.c | 51 +++++++++++++++++++++++++++++++++++
> 3 files changed, 70 insertions(+), 1 deletion(-)
>
[...]
> + buf[0] = '\0';
> + ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
> + buf, sizeof(buf));
> + if (ret < 0)
> + return libbpf_err(ret);
> +
> + if (ret > 0)
> + return 1; /* assume supported */
> +
> + /* If BPF verifier recognizes BPF kfunc but it's not supported for
> + * given BPF program type, it will emit "calling kernel function
> + * <name> is not allowed". If the kfunc id is invalid,
> + * it will emit "kernel btf_id <id> is not a function". If BTF fd
> + * invalid in module BTF, it will emit "invalid module BTF fd specified" or
> + * "negative offset disallowed for kernel module function call". If
> + * kfunc prog not dev buound, it will emit "metadata kfuncs require
> + * device-bound program".
> + */
> + if (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
> + strstr(buf, "invalid module BTF fd") ||
why is invalid module BTF FD not an error (negative return)?
> + strstr(buf, "negative offset disallowed") ||
> + strstr(buf, "device-bound program"))
> + return 0;
> +
> + return 1;
> +}
> +
> int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
> const void *opts)
> {
> --
> 2.43.0
>
在 2025/2/25 09:15, Andrii Nakryiko 写道:
> On Mon, Feb 24, 2025 at 9:02 AM Tao Chen <chen.dylane@linux.dev> wrote:
>>
>> Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
>> used to test the availability of the different eBPF kfuncs on the
>> current system.
>>
>> Cc: Tao Chen <dylane.chen@didiglobal.com>
>> Reviewed-by: Jiri Olsa <jolsa@kernel.org>
>> Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
>> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
>> ---
>> tools/lib/bpf/libbpf.h | 19 ++++++++++++-
>> tools/lib/bpf/libbpf.map | 1 +
>> tools/lib/bpf/libbpf_probes.c | 51 +++++++++++++++++++++++++++++++++++
>> 3 files changed, 70 insertions(+), 1 deletion(-)
>>
>
> [...]
>
>> + buf[0] = '\0';
>> + ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
>> + buf, sizeof(buf));
>> + if (ret < 0)
>> + return libbpf_err(ret);
>> +
>> + if (ret > 0)
>> + return 1; /* assume supported */
>> +
>> + /* If BPF verifier recognizes BPF kfunc but it's not supported for
>> + * given BPF program type, it will emit "calling kernel function
>> + * <name> is not allowed". If the kfunc id is invalid,
>> + * it will emit "kernel btf_id <id> is not a function". If BTF fd
>> + * invalid in module BTF, it will emit "invalid module BTF fd specified" or
>> + * "negative offset disallowed for kernel module function call". If
>> + * kfunc prog not dev buound, it will emit "metadata kfuncs require
>> + * device-bound program".
>> + */
>> + if (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
>> + strstr(buf, "invalid module BTF fd") ||
>
> why is invalid module BTF FD not an error (negative return)?
>
>> + strstr(buf, "negative offset disallowed") ||
>> + strstr(buf, "device-bound program"))
>> + return 0;
>> +
>> + return 1;
>> +}
>> +
>> int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>> const void *opts)
>> {
>> --
>> 2.43.0
>>
In probe_prog_load, err will be checked and converted into either 0 or 1.
--
Best Regards
Tao Chen
On Mon, Feb 24, 2025 at 9:47 PM Tao Chen <chen.dylane@linux.dev> wrote:
>
> 在 2025/2/25 09:15, Andrii Nakryiko 写道:
> > On Mon, Feb 24, 2025 at 9:02 AM Tao Chen <chen.dylane@linux.dev> wrote:
> >>
> >> Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
> >> used to test the availability of the different eBPF kfuncs on the
> >> current system.
> >>
> >> Cc: Tao Chen <dylane.chen@didiglobal.com>
> >> Reviewed-by: Jiri Olsa <jolsa@kernel.org>
> >> Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
> >> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
> >> ---
> >> tools/lib/bpf/libbpf.h | 19 ++++++++++++-
> >> tools/lib/bpf/libbpf.map | 1 +
> >> tools/lib/bpf/libbpf_probes.c | 51 +++++++++++++++++++++++++++++++++++
> >> 3 files changed, 70 insertions(+), 1 deletion(-)
> >>
> >
> > [...]
> >
> >> + buf[0] = '\0';
> >> + ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
> >> + buf, sizeof(buf));
> >> + if (ret < 0)
> >> + return libbpf_err(ret);
> >> +
> >> + if (ret > 0)
> >> + return 1; /* assume supported */
> >> +
> >> + /* If BPF verifier recognizes BPF kfunc but it's not supported for
> >> + * given BPF program type, it will emit "calling kernel function
> >> + * <name> is not allowed". If the kfunc id is invalid,
> >> + * it will emit "kernel btf_id <id> is not a function". If BTF fd
> >> + * invalid in module BTF, it will emit "invalid module BTF fd specified" or
> >> + * "negative offset disallowed for kernel module function call". If
> >> + * kfunc prog not dev buound, it will emit "metadata kfuncs require
> >> + * device-bound program".
> >> + */
> >> + if (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
> >> + strstr(buf, "invalid module BTF fd") ||
> >
> > why is invalid module BTF FD not an error (negative return)?
> >
> >> + strstr(buf, "negative offset disallowed") ||
> >> + strstr(buf, "device-bound program"))
> >> + return 0;
> >> +
> >> + return 1;
> >> +}
> >> +
> >> int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
> >> const void *opts)
> >> {
> >> --
> >> 2.43.0
> >>
>
> In probe_prog_load, err will be checked and converted into either 0 or 1.
I guess what I was getting at is that providing invalid module BTF FD
is not a "not supported" case, it's an error case (and so should
result in negative return)
>
> --
> Best Regards
> Tao Chen
© 2016 - 2025 Red Hat, Inc.