[PATCH bpf-next 0/2] tools/bpf: two changes in libbpf

[PATCH bpf-next 0/2] tools/bpf: two changes in libbpf

[Yonghong Song]

Two changes in libbpf. Patch #1 adds "const" qualifier to parameter
"map_name" of function btf__get_map_kv_tids().
Patch #2 adds log_level to structure bpf_load_program_attr so
verifier log level 2 can be used with api function
bpf_load_program_xattr(). Please see individual patches for details.

Yonghong Song (2):
  tools/bpf: add const qualifier to btf__get_map_kv_tids() map_name
    parameter
  tools/bpf: add log_level to bpf_load_program_attr

 tools/lib/bpf/bpf.c                     | 4 +++-
 tools/lib/bpf/bpf.h                     | 1 +
 tools/lib/bpf/btf.c                     | 2 +-
 tools/lib/bpf/btf.h                     | 2 +-
 tools/testing/selftests/bpf/test_sock.c | 9 ++++++++-
 5 files changed, 14 insertions(+), 4 deletions(-)

-- 
2.17.1

[PATCH bpf-next 1/2] tools/bpf: add const qualifier to btf__get_map_kv_tids() map_name parameter

[Yonghong Song]

Commit 96408c43447a ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
added the API function btf__get_map_kv_tids():
  btf__get_map_kv_tids(const struct btf *btf, char *map_name, ...)

The parameter map_name has type "char *". This is okay inside libbpf library since
the map_name is from bpf_map->name which also has type "char *".

This will be problematic if the caller for map_name already has attribute "const",
e.g., from C++ string.c_str(). It will result in either a warning or an error.

  /home/yhs/work/bcc/src/cc/btf.cc:166:51:
    error: invalid conversion from ‘const char*’ to ‘char*’ [-fpermissive]
      return btf__get_map_kv_tids(btf_, map_name.c_str()

This patch added "const" attributes to map_name parameter.

Fixes: 96408c43447a ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/lib/bpf/btf.c | 2 +-
 tools/lib/bpf/btf.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 4949f8840bda..3b3a2959d03a 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -511,7 +511,7 @@ int btf__get_from_id(__u32 id, struct btf **btf)
 	return err;
 }
 
-int btf__get_map_kv_tids(const struct btf *btf, char *map_name,
+int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
 			 __u32 expected_key_size, __u32 expected_value_size,
 			 __u32 *key_type_id, __u32 *value_type_id)
 {
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 25a9d2db035d..b393da90cc85 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -69,7 +69,7 @@ LIBBPF_API void btf__get_strings(const struct btf *btf, const char **strings,
 				 __u32 *str_len);
 LIBBPF_API const char *btf__name_by_offset(const struct btf *btf, __u32 offset);
 LIBBPF_API int btf__get_from_id(__u32 id, struct btf **btf);
-LIBBPF_API int btf__get_map_kv_tids(const struct btf *btf, char *map_name,
+LIBBPF_API int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
 				    __u32 expected_key_size,
 				    __u32 expected_value_size,
 				    __u32 *key_type_id, __u32 *value_type_id);
-- 
2.17.1

[PATCH bpf-next 2/2] tools/bpf: add log_level to bpf_load_program_attr

[Yonghong Song]

The kernel verifier has three levels of logs:
    0: no logs
    1: logs mostly useful
  > 1: verbose

Current libbpf API functions bpf_load_program_xattr() and
bpf_load_program() cannot specify log_level.
The bcc, however, provides an interface for user to
specify log_level 2 for verbose output.

This patch added log_level into structure
bpf_load_program_attr, so users, including bcc, can use
bpf_load_program_xattr() to change log_level.

The bpf selftest test_sock.c is modified to enable log_level = 2.
If the "verbose" in test_sock.c is changed to true,
the test will output logs like below:
  $ ./test_sock
  func#0 @0
  0: R1=ctx(id=0,off=0,imm=0) R10=fp0,call_-1
  0: (bf) r6 = r1
  1: R1=ctx(id=0,off=0,imm=0) R6_w=ctx(id=0,off=0,imm=0) R10=fp0,call_-1
  1: (61) r7 = *(u32 *)(r6 +28)
  invalid bpf_context access off=28 size=4

  Test case: bind4 load with invalid access: src_ip6 .. [PASS]
  ...
  Test case: bind6 allow all .. [PASS]
  Summary: 16 PASSED, 0 FAILED

Some test_sock tests are negative tests and verbose verifier
log will be printed out as shown in the above.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/lib/bpf/bpf.c                     | 4 +++-
 tools/lib/bpf/bpf.h                     | 1 +
 tools/testing/selftests/bpf/test_sock.c | 9 ++++++++-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 3defad77dc7a..78aa8c2b1a5c 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -214,6 +214,7 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 {
 	void *finfo = NULL, *linfo = NULL;
 	union bpf_attr attr;
+	__u32 log_level;
 	__u32 name_len;
 	int fd;
 
@@ -292,7 +293,8 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 	/* Try again with log */
 	attr.log_buf = ptr_to_u64(log_buf);
 	attr.log_size = log_buf_sz;
-	attr.log_level = 1;
+	log_level = load_attr->log_level;
+	attr.log_level = (log_level >= 2) ? log_level : 1;
 	log_buf[0] = 0;
 	fd = sys_bpf_prog_load(&attr, sizeof(attr));
 done:
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index ed09eed2dc3b..15a8e22e8eae 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -76,6 +76,7 @@ struct bpf_load_program_attr {
 	const struct bpf_insn *insns;
 	size_t insns_cnt;
 	const char *license;
+	__u32 log_level;
 	__u32 kern_version;
 	__u32 prog_ifindex;
 	__u32 prog_btf_fd;
diff --git a/tools/testing/selftests/bpf/test_sock.c b/tools/testing/selftests/bpf/test_sock.c
index 561ffb6d6433..fb679ac3d4b0 100644
--- a/tools/testing/selftests/bpf/test_sock.c
+++ b/tools/testing/selftests/bpf/test_sock.c
@@ -20,6 +20,7 @@
 #define MAX_INSNS	512
 
 char bpf_log_buf[BPF_LOG_BUF_SIZE];
+static bool verbose = false;
 
 struct sock_test {
 	const char *descr;
@@ -325,6 +326,7 @@ static int load_sock_prog(const struct bpf_insn *prog,
 			  enum bpf_attach_type attach_type)
 {
 	struct bpf_load_program_attr attr;
+	int ret;
 
 	memset(&attr, 0, sizeof(struct bpf_load_program_attr));
 	attr.prog_type = BPF_PROG_TYPE_CGROUP_SOCK;
@@ -332,8 +334,13 @@ static int load_sock_prog(const struct bpf_insn *prog,
 	attr.insns = prog;
 	attr.insns_cnt = probe_prog_length(attr.insns);
 	attr.license = "GPL";
+	attr.log_level = 2;
 
-	return bpf_load_program_xattr(&attr, bpf_log_buf, BPF_LOG_BUF_SIZE);
+	ret = bpf_load_program_xattr(&attr, bpf_log_buf, BPF_LOG_BUF_SIZE);
+	if (verbose && ret < 0)
+		fprintf(stderr, "%s\n", bpf_log_buf);
+
+	return ret;
 }
 
 static int attach_sock_prog(int cgfd, int progfd,
-- 
2.17.1

Re: [PATCH bpf-next 2/2] tools/bpf: add log_level to bpf_load_program_attr

[Alexei Starovoitov]

On Tue, Feb 05, 2019 at 11:48:23AM -0800, Yonghong Song wrote:
> The kernel verifier has three levels of logs:
>     0: no logs
>     1: logs mostly useful
>   > 1: verbose
> 
> Current libbpf API functions bpf_load_program_xattr() and
> bpf_load_program() cannot specify log_level.
> The bcc, however, provides an interface for user to
> specify log_level 2 for verbose output.
> 
> This patch added log_level into structure
> bpf_load_program_attr, so users, including bcc, can use
> bpf_load_program_xattr() to change log_level.
> 
> The bpf selftest test_sock.c is modified to enable log_level = 2.
> If the "verbose" in test_sock.c is changed to true,
> the test will output logs like below:
>   $ ./test_sock
>   func#0 @0
>   0: R1=ctx(id=0,off=0,imm=0) R10=fp0,call_-1
>   0: (bf) r6 = r1
>   1: R1=ctx(id=0,off=0,imm=0) R6_w=ctx(id=0,off=0,imm=0) R10=fp0,call_-1
>   1: (61) r7 = *(u32 *)(r6 +28)
>   invalid bpf_context access off=28 size=4
> 
>   Test case: bind4 load with invalid access: src_ip6 .. [PASS]
>   ...
>   Test case: bind6 allow all .. [PASS]
>   Summary: 16 PASSED, 0 FAILED
> 
> Some test_sock tests are negative tests and verbose verifier
> log will be printed out as shown in the above.
> 
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  tools/lib/bpf/bpf.c                     | 4 +++-
>  tools/lib/bpf/bpf.h                     | 1 +
>  tools/testing/selftests/bpf/test_sock.c | 9 ++++++++-
>  3 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 3defad77dc7a..78aa8c2b1a5c 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -214,6 +214,7 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
>  {
>  	void *finfo = NULL, *linfo = NULL;
>  	union bpf_attr attr;
> +	__u32 log_level;
>  	__u32 name_len;
>  	int fd;
>  
> @@ -292,7 +293,8 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
>  	/* Try again with log */
>  	attr.log_buf = ptr_to_u64(log_buf);
>  	attr.log_size = log_buf_sz;
> -	attr.log_level = 1;
> +	log_level = load_attr->log_level;
> +	attr.log_level = (log_level >= 2) ? log_level : 1;
>  	log_buf[0] = 0;
>  	fd = sys_bpf_prog_load(&attr, sizeof(attr));
>  done:
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index ed09eed2dc3b..15a8e22e8eae 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -76,6 +76,7 @@ struct bpf_load_program_attr {
>  	const struct bpf_insn *insns;
>  	size_t insns_cnt;
>  	const char *license;
> +	__u32 log_level;
>  	__u32 kern_version;
>  	__u32 prog_ifindex;
>  	__u32 prog_btf_fd;

this will break binary compatibility in libbpf api.
Please add new fields always to the end of *_attr structs.

Also why not to silence bcc instead?
Let it treat log_level > 1 as log_level=1
I don't think anyone but the most extreme verifier hacker used level=2.
Personally I don't remember when was the last time I used it.
It seem like a niche feature that we can safely remove in bcc.

Re: [PATCH bpf-next 1/2] tools/bpf: add const qualifier to btf__get_map_kv_tids() map_name parameter

[Alexei Starovoitov]

On Tue, Feb 05, 2019 at 11:48:22AM -0800, Yonghong Song wrote:
> Commit 96408c43447a ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
> added the API function btf__get_map_kv_tids():
>   btf__get_map_kv_tids(const struct btf *btf, char *map_name, ...)
> 
> The parameter map_name has type "char *". This is okay inside libbpf library since
> the map_name is from bpf_map->name which also has type "char *".
> 
> This will be problematic if the caller for map_name already has attribute "const",
> e.g., from C++ string.c_str(). It will result in either a warning or an error.
> 
>   /home/yhs/work/bcc/src/cc/btf.cc:166:51:
>     error: invalid conversion from ‘const char*’ to ‘char*’ [-fpermissive]
>       return btf__get_map_kv_tids(btf_, map_name.c_str()
> 
> This patch added "const" attributes to map_name parameter.
> 
> Fixes: 96408c43447a ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
> Signed-off-by: Yonghong Song <yhs@fb.com>

Acked-by: Alexei Starovoitov <ast@kernel.org>

Re: [PATCH bpf-next 1/2] tools/bpf: add const qualifier to btf__get_map_kv_tids() map_name parameter

[Alexei Starovoitov]

On Tue, Feb 5, 2019 at 6:27 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Feb 05, 2019 at 11:48:22AM -0800, Yonghong Song wrote:
> > Commit 96408c43447a ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
> > added the API function btf__get_map_kv_tids():
> >   btf__get_map_kv_tids(const struct btf *btf, char *map_name, ...)
> >
> > The parameter map_name has type "char *". This is okay inside libbpf library since
> > the map_name is from bpf_map->name which also has type "char *".
> >
> > This will be problematic if the caller for map_name already has attribute "const",
> > e.g., from C++ string.c_str(). It will result in either a warning or an error.
> >
> >   /home/yhs/work/bcc/src/cc/btf.cc:166:51:
> >     error: invalid conversion from ‘const char*’ to ‘char*’ [-fpermissive]
> >       return btf__get_map_kv_tids(btf_, map_name.c_str()
> >
> > This patch added "const" attributes to map_name parameter.
> >
> > Fixes: 96408c43447a ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
> > Signed-off-by: Yonghong Song <yhs@fb.com>
>
> Acked-by: Alexei Starovoitov <ast@kernel.org>

Actually just applied this patch alone,
since it's independent from 2nd.

Re: [PATCH bpf-next 2/2] tools/bpf: add log_level to bpf_load_program_attr

[Yonghong Song]

On 2/5/19 6:26 PM, Alexei Starovoitov wrote:
> On Tue, Feb 05, 2019 at 11:48:23AM -0800, Yonghong Song wrote:
>> The kernel verifier has three levels of logs:
>>      0: no logs
>>      1: logs mostly useful
>>    > 1: verbose
>>
>> Current libbpf API functions bpf_load_program_xattr() and
>> bpf_load_program() cannot specify log_level.
>> The bcc, however, provides an interface for user to
>> specify log_level 2 for verbose output.
>>
>> This patch added log_level into structure
>> bpf_load_program_attr, so users, including bcc, can use
>> bpf_load_program_xattr() to change log_level.
>>
>> The bpf selftest test_sock.c is modified to enable log_level = 2.
>> If the "verbose" in test_sock.c is changed to true,
>> the test will output logs like below:
>>    $ ./test_sock
>>    func#0 @0
>>    0: R1=ctx(id=0,off=0,imm=0) R10=fp0,call_-1
>>    0: (bf) r6 = r1
>>    1: R1=ctx(id=0,off=0,imm=0) R6_w=ctx(id=0,off=0,imm=0) R10=fp0,call_-1
>>    1: (61) r7 = *(u32 *)(r6 +28)
>>    invalid bpf_context access off=28 size=4
>>
>>    Test case: bind4 load with invalid access: src_ip6 .. [PASS]
>>    ...
>>    Test case: bind6 allow all .. [PASS]
>>    Summary: 16 PASSED, 0 FAILED
>>
>> Some test_sock tests are negative tests and verbose verifier
>> log will be printed out as shown in the above.
>>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>> ---
>>   tools/lib/bpf/bpf.c                     | 4 +++-
>>   tools/lib/bpf/bpf.h                     | 1 +
>>   tools/testing/selftests/bpf/test_sock.c | 9 ++++++++-
>>   3 files changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
>> index 3defad77dc7a..78aa8c2b1a5c 100644
>> --- a/tools/lib/bpf/bpf.c
>> +++ b/tools/lib/bpf/bpf.c
>> @@ -214,6 +214,7 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
>>   {
>>   	void *finfo = NULL, *linfo = NULL;
>>   	union bpf_attr attr;
>> +	__u32 log_level;
>>   	__u32 name_len;
>>   	int fd;
>>   
>> @@ -292,7 +293,8 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
>>   	/* Try again with log */
>>   	attr.log_buf = ptr_to_u64(log_buf);
>>   	attr.log_size = log_buf_sz;
>> -	attr.log_level = 1;
>> +	log_level = load_attr->log_level;
>> +	attr.log_level = (log_level >= 2) ? log_level : 1;
>>   	log_buf[0] = 0;
>>   	fd = sys_bpf_prog_load(&attr, sizeof(attr));
>>   done:
>> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
>> index ed09eed2dc3b..15a8e22e8eae 100644
>> --- a/tools/lib/bpf/bpf.h
>> +++ b/tools/lib/bpf/bpf.h
>> @@ -76,6 +76,7 @@ struct bpf_load_program_attr {
>>   	const struct bpf_insn *insns;
>>   	size_t insns_cnt;
>>   	const char *license;
>> +	__u32 log_level;
>>   	__u32 kern_version;
>>   	__u32 prog_ifindex;
>>   	__u32 prog_btf_fd;
> 
> this will break binary compatibility in libbpf api.
> Please add new fields always to the end of *_attr structs.

I felt that we were still at 0.0.x stage and still could tweak
the api a little bit so I used the above sequence to
mimic the kernel prog_load attr sequence. I do agree that
in general we should add to the end of data structure.
I can change to the end of structure we still decided
if exposing log_level=2 is needed.

> 
> Also why not to silence bcc instead?
> Let it treat log_level > 1 as log_level=1
> I don't think anyone but the most extreme verifier hacker used level=2.

In general, that is true. I just used the feature a couple of
weeks ago to toubleshoot a verifier error... But most cases
log_level=1 should be sufficient.

> Personally I don't remember when was the last time I used it.
> It seem like a niche feature that we can safely remove in bcc.
Will discuss a little more in bcc community and then make
a decision.