tools/bpf: add log_level to bpf_load_program_attr

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
supported log_level is 0, 1, and 2.

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

tools/lib/bpf/bpf.c

@@ -215,10 +215,15 @@ 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;
 
-	if (!load_attr)
+	if (!load_attr || !log_buf != !log_buf_sz)
+		return -EINVAL;
+
+	log_level = load_attr->log_level;
+	if (log_level > 2 || (log_level && !log_buf))
 		return -EINVAL;
 
 	name_len = load_attr->name ? strlen(load_attr->name) : 0;
@@ -229,9 +234,16 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 	attr.insn_cnt = (__u32)load_attr->insns_cnt;
 	attr.insns = ptr_to_u64(load_attr->insns);
 	attr.license = ptr_to_u64(load_attr->license);
-	attr.log_buf = ptr_to_u64(NULL);
-	attr.log_size = 0;
-	attr.log_level = 0;
+
+	attr.log_level = log_level;
+	if (log_level) {
+		attr.log_buf = ptr_to_u64(log_buf);
+		attr.log_size = log_buf_sz;
+	} else {
+		attr.log_buf = ptr_to_u64(NULL);
+		attr.log_size = 0;
+	}
+
 	attr.kern_version = load_attr->kern_version;
 	attr.prog_ifindex = load_attr->prog_ifindex;
 	attr.prog_btf_fd = load_attr->prog_btf_fd;
@@ -287,7 +299,7 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 			goto done;
 	}
 
-	if (!log_buf || !log_buf_sz)
+	if (log_level || !log_buf)
 		goto done;
 
 	/* Try again with log */

tools/lib/bpf/bpf.h

@@ -85,6 +85,7 @@ struct bpf_load_program_attr {
 	__u32 line_info_rec_size;
 	const void *line_info;
 	__u32 line_info_cnt;
+	__u32 log_level;
 };
 
 /* Flags to direct loading requirements */

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,