commit da11b417583ece875f862d84578259a2ab27ad86
author Alexei Starovoitov <ast@kernel.org> Mon Apr 01 21:27:47 2019 -0700
committer Daniel Borkmann <daniel@iogearbox.net> Thu Apr 04 01:27:38 2019 +0200
tree 788118532f64d3e719781ebf2f4ba3fcc679fe14
parent 7a9f5c65abcc9644b11738ca0815510cb5510eaf

libbpf: teach libbpf about log_level bit 2

Allow bpf_prog_load_xattr() to specify log_level for program loading.

Teach libbpf to accept log_level with bit 2 set.

Increase default BPF_LOG_BUF_SIZE from 256k to 16M.
There is no downside to increase it to a maximum allowed by old kernels.
Existing 256k limit caused ENOSPC errors and users were not able to see
verifier error which is printed at the end of the verifier log.

If ENOSPC is hit, double the verifier log and try again to capture
the verifier error.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/bpf.c

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 9cd0155..a1db869 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -223,7 +223,7 @@
 		return -EINVAL;
 
 	log_level = load_attr->log_level;
-	if (log_level > 2 || (log_level && !log_buf))
+	if (log_level > (4 | 2 | 1) || (log_level && !log_buf))
 		return -EINVAL;
 
 	name_len = load_attr->name ? strlen(load_attr->name) : 0;

tools/lib/bpf/bpf.h

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 6ffdd79..e2c0df7 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -92,7 +92,7 @@
 #define MAPS_RELAX_COMPAT	0x01
 
 /* Recommend log buffer size */
-#define BPF_LOG_BUF_SIZE (256 * 1024)
+#define BPF_LOG_BUF_SIZE (16 * 1024 * 1024) /* verifier maximum in kernels <= 5.1 */
 LIBBPF_API int
 bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 		       char *log_buf, size_t log_buf_sz);

tools/lib/bpf/libbpf.c

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 11c25d9..e1e4d35 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -152,6 +152,7 @@
 		};
 	} *reloc_desc;
 	int nr_reloc;
+	int log_level;
 
 	struct {
 		int nr;
@@ -1494,6 +1495,7 @@
 {
 	struct bpf_load_program_attr load_attr;
 	char *cp, errmsg[STRERR_BUFSIZE];
+	int log_buf_size = BPF_LOG_BUF_SIZE;
 	char *log_buf;
 	int ret;
 
@@ -1514,21 +1516,30 @@
 	load_attr.line_info = prog->line_info;
 	load_attr.line_info_rec_size = prog->line_info_rec_size;
 	load_attr.line_info_cnt = prog->line_info_cnt;
+	load_attr.log_level = prog->log_level;
 	if (!load_attr.insns || !load_attr.insns_cnt)
 		return -EINVAL;
 
-	log_buf = malloc(BPF_LOG_BUF_SIZE);
+retry_load:
+	log_buf = malloc(log_buf_size);
 	if (!log_buf)
 		pr_warning("Alloc log buffer for bpf loader error, continue without log\n");
 
-	ret = bpf_load_program_xattr(&load_attr, log_buf, BPF_LOG_BUF_SIZE);
+	ret = bpf_load_program_xattr(&load_attr, log_buf, log_buf_size);
 
 	if (ret >= 0) {
+		if (load_attr.log_level)
+			pr_debug("verifier log:\n%s", log_buf);
 		*pfd = ret;
 		ret = 0;
 		goto out;
 	}
 
+	if (errno == ENOSPC) {
+		log_buf_size <<= 1;
+		free(log_buf);
+		goto retry_load;
+	}
 	ret = -LIBBPF_ERRNO__LOAD;
 	cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
 	pr_warning("load bpf program failed: %s\n", cp);
@@ -2938,6 +2949,7 @@
 		bpf_program__set_expected_attach_type(prog,
 						      expected_attach_type);
 
+		prog->log_level = attr->log_level;
 		if (!first_prog)
 			first_prog = prog;
 	}

tools/lib/bpf/libbpf.h

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index c70785c..5313233 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -314,6 +314,7 @@
 	enum bpf_prog_type prog_type;
 	enum bpf_attach_type expected_attach_type;
 	int ifindex;
+	int log_level;
 };
 
 LIBBPF_API int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,