[bpf-next,v3,2/3] libbpf: Add libbpf_probe_bpf_kfunc API

Commit Message

Tao Chen Jan. 24, 2025, 2:44 p.m. UTC

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.

Signed-off-by: Tao Chen <[e-mail]>
---
 tools/lib/bpf/libbpf.h        | 17 ++++++++++++++++-
 tools/lib/bpf/libbpf.map      |  1 +
 tools/lib/bpf/libbpf_probes.c | 30 ++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 1 deletion(-)

Comments

Jiri Olsa Jan. 24, 2025, 4:27 p.m. UTC | #1

On Fri, Jan 24, 2025 at 10:44:10PM +0800, Tao Chen 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.
> 
> Signed-off-by: Tao Chen <[e-mail]>
> ---
>  tools/lib/bpf/libbpf.h        | 17 ++++++++++++++++-
>  tools/lib/bpf/libbpf.map      |  1 +
>  tools/lib/bpf/libbpf_probes.c | 30 ++++++++++++++++++++++++++++++
>  3 files changed, 47 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 3020ee45303a..035829e22099 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -1680,7 +1680,22 @@ 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, 0 for 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, __s16 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;
>  } LIBBPF_1.5.0;
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index b73345977b4e..cd7d16c1cc49 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -446,6 +446,36 @@ static int probe_func_comm(enum bpf_prog_type prog_type, struct bpf_insn insn,
>  	return 0;
>  }
>  
> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id,
> +			   __s16 btf_fd, const void *opts)
> +{
> +	struct bpf_insn insn;
> +	int err;
> +	char buf[4096];
> +
> +	if (opts)
> +		return libbpf_err(-EINVAL);
> +
> +	insn.code = BPF_JMP | BPF_CALL;
> +	insn.src_reg = BPF_PSEUDO_KFUNC_CALL;
> +	insn.imm = kfunc_id;
> +	insn.off = btf_fd;

nit, you could use

        struct bpf_insn insns[] = {
        	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, off, imm),
                BPF_EXIT_INSN(),
        };

jirka

> +
> +	err = probe_func_comm(prog_type, insn, buf, sizeof(buf));
> +	if (err)
> +		return err;
> +
> +	/* If BPF verifier recognizes BPF kfunc but it's not supported for
> +	 * given BPF program type, it will emit "calling kernel function
> +	 * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
> +	 * it will emit "kernel btf_id 4294967295 is not a function".
> +	 */
> +	if (err == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function")))
> +		return 0;
> +
> +	return 1; /* assume supported */
> +}
> +
>  int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>  			    const void *opts)
>  {
> -- 
> 2.43.0
>

Andrii Nakryiko Jan. 24, 2025, 6:46 p.m. UTC | #2

On Fri, Jan 24, 2025 at 6:44 AM Tao Chen <[e-mail]> 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.
>
> Signed-off-by: Tao Chen <[e-mail]>
> ---
>  tools/lib/bpf/libbpf.h        | 17 ++++++++++++++++-
>  tools/lib/bpf/libbpf.map      |  1 +
>  tools/lib/bpf/libbpf_probes.c | 30 ++++++++++++++++++++++++++++++
>  3 files changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 3020ee45303a..035829e22099 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -1680,7 +1680,22 @@ 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, 0 for 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, __s16 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;
>  } LIBBPF_1.5.0;
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index b73345977b4e..cd7d16c1cc49 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -446,6 +446,36 @@ static int probe_func_comm(enum bpf_prog_type prog_type, struct bpf_insn insn,
>         return 0;
>  }
>
> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id,
> +                          __s16 btf_fd, const void *opts)

btf_fd should be int (and mention in documentation that if kfunc is
defined in kernel module btf_fd is used to point to module's BTF)

> +{
> +       struct bpf_insn insn;
> +       int err;
> +       char buf[4096];
> +
> +       if (opts)
> +               return libbpf_err(-EINVAL);
> +
> +       insn.code = BPF_JMP | BPF_CALL;
> +       insn.src_reg = BPF_PSEUDO_KFUNC_CALL;
> +       insn.imm = kfunc_id;
> +       insn.off = btf_fd;
> +
> +       err = probe_func_comm(prog_type, insn, buf, sizeof(buf));
> +       if (err)
> +               return err;
> +
> +       /* If BPF verifier recognizes BPF kfunc but it's not supported for
> +        * given BPF program type, it will emit "calling kernel function
> +        * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
> +        * it will emit "kernel btf_id 4294967295 is not a function".
> +        */
> +       if (err == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function")))
> +               return 0;
> +
> +       return 1; /* assume supported */
> +}
> +
>  int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>                             const void *opts)
>  {
> --
> 2.43.0
>

Tao Chen Jan. 25, 2025, 2:54 p.m. UTC | #3

在 2025/1/25 00:27, Jiri Olsa 写道:
> On Fri, Jan 24, 2025 at 10:44:10PM +0800, Tao Chen 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.
>>
>> Signed-off-by: Tao Chen <[e-mail]>
>> ---
>>   tools/lib/bpf/libbpf.h        | 17 ++++++++++++++++-
>>   tools/lib/bpf/libbpf.map      |  1 +
>>   tools/lib/bpf/libbpf_probes.c | 30 ++++++++++++++++++++++++++++++
>>   3 files changed, 47 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
>> index 3020ee45303a..035829e22099 100644
>> --- a/tools/lib/bpf/libbpf.h
>> +++ b/tools/lib/bpf/libbpf.h
>> @@ -1680,7 +1680,22 @@ 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, 0 for 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, __s16 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;
>>   } LIBBPF_1.5.0;
>> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
>> index b73345977b4e..cd7d16c1cc49 100644
>> --- a/tools/lib/bpf/libbpf_probes.c
>> +++ b/tools/lib/bpf/libbpf_probes.c
>> @@ -446,6 +446,36 @@ static int probe_func_comm(enum bpf_prog_type prog_type, struct bpf_insn insn,
>>   	return 0;
>>   }
>>   
>> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id,
>> +			   __s16 btf_fd, const void *opts)
>> +{
>> +	struct bpf_insn insn;
>> +	int err;
>> +	char buf[4096];
>> +
>> +	if (opts)
>> +		return libbpf_err(-EINVAL);
>> +
>> +	insn.code = BPF_JMP | BPF_CALL;
>> +	insn.src_reg = BPF_PSEUDO_KFUNC_CALL;
>> +	insn.imm = kfunc_id;
>> +	insn.off = btf_fd;
> 
> nit, you could use
> 
>          struct bpf_insn insns[] = {
>          	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, off, imm),
>                  BPF_EXIT_INSN(),
>          };
> 
> jirka
> 

Yeah, it looks more concise, i will send it in v4. Thanks.

>> +
>> +	err = probe_func_comm(prog_type, insn, buf, sizeof(buf));
>> +	if (err)
>> +		return err;
>> +
>> +	/* If BPF verifier recognizes BPF kfunc but it's not supported for
>> +	 * given BPF program type, it will emit "calling kernel function
>> +	 * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
>> +	 * it will emit "kernel btf_id 4294967295 is not a function".
>> +	 */
>> +	if (err == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function")))
>> +		return 0;
>> +
>> +	return 1; /* assume supported */
>> +}
>> +
>>   int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>>   			    const void *opts)
>>   {
>> -- 
>> 2.43.0
>>

Patch

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 3020ee45303a..035829e22099 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1680,7 +1680,22 @@  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, 0 for 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, __s16 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;
 } LIBBPF_1.5.0;
diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index b73345977b4e..cd7d16c1cc49 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -446,6 +446,36 @@  static int probe_func_comm(enum bpf_prog_type prog_type, struct bpf_insn insn,
 	return 0;
 }
 
+int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id,
+			   __s16 btf_fd, const void *opts)
+{
+	struct bpf_insn insn;
+	int err;
+	char buf[4096];
+
+	if (opts)
+		return libbpf_err(-EINVAL);
+
+	insn.code = BPF_JMP | BPF_CALL;
+	insn.src_reg = BPF_PSEUDO_KFUNC_CALL;
+	insn.imm = kfunc_id;
+	insn.off = btf_fd;
+
+	err = probe_func_comm(prog_type, insn, buf, sizeof(buf));
+	if (err)
+		return err;
+
+	/* If BPF verifier recognizes BPF kfunc but it's not supported for
+	 * given BPF program type, it will emit "calling kernel function
+	 * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
+	 * it will emit "kernel btf_id 4294967295 is not a function".
+	 */
+	if (err == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function")))
+		return 0;
+
+	return 1; /* assume supported */
+}
+
 int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
 			    const void *opts)
 {