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

[Yonghong Song <yhs@fb.com>]

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