[PATCH v4 bpf-next 16/19] libbpf: wire through log_true_size for bpf_btf_load() API

[Andrii Nakryiko <andrii@kernel.org>]

Similar to what we did for bpf_prog_load() in previous patch, wire
returning of log_true_size value from kernel back to the user through
OPTS out field.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/bpf.c |  6 ++++--
 tools/lib/bpf/bpf.h | 11 +++++++++--
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index a031de0a707a..128ac723c4ea 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -1083,9 +1083,9 @@ int bpf_raw_tracepoint_open(const char *name, int prog_fd)
 	return libbpf_err_errno(fd);
 }
 
-int bpf_btf_load(const void *btf_data, size_t btf_size, const struct bpf_btf_load_opts *opts)
+int bpf_btf_load(const void *btf_data, size_t btf_size, struct bpf_btf_load_opts *opts)
 {
-	const size_t attr_sz = offsetofend(union bpf_attr, btf_log_level);
+	const size_t attr_sz = offsetofend(union bpf_attr, btf_log_true_size);
 	union bpf_attr attr;
 	char *log_buf;
 	size_t log_size;
@@ -1128,6 +1128,8 @@ int bpf_btf_load(const void *btf_data, size_t btf_size, const struct bpf_btf_loa
 		attr.btf_log_level = 1;
 		fd = sys_bpf_fd(BPF_BTF_LOAD, &attr, attr_sz);
 	}
+
+	OPTS_SET(opts, log_true_size, attr.btf_log_true_size);
 	return libbpf_err_errno(fd);
 }
 
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index cfa0cdfa50f8..a2c091389b18 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -124,11 +124,18 @@ struct bpf_btf_load_opts {
 	char *log_buf;
 	__u32 log_level;
 	__u32 log_size;
+	/* output: actual total log contents size (including termintaing zero).
+	 * It could be both larger than original log_size (if log was
+	 * truncated), or smaller (if log buffer wasn't filled completely).
+	 * If kernel doesn't support this feature, log_size is left unchanged.
+	 */
+	__u32 log_true_size;
+	size_t :0;
 };
-#define bpf_btf_load_opts__last_field log_size
+#define bpf_btf_load_opts__last_field log_true_size
 
 LIBBPF_API int bpf_btf_load(const void *btf_data, size_t btf_size,
-			    const struct bpf_btf_load_opts *opts);
+			    struct bpf_btf_load_opts *opts);
 
 LIBBPF_API int bpf_map_update_elem(int fd, const void *key, const void *value,
 				   __u64 flags);
-- 
2.34.1