[RFC PATCH bpf-next v2 5/6] libbpf: Add common attr support for map_create

[Leon Hwang <leon.hwang@linux.dev>]

With the previous patch adding common attribute support for
BPF_MAP_CREATE, it is now possible to retrieve detailed error messages
when map creation fails by using the 'log_buf' field from the common
attributes.

This patch extends 'bpf_map_create_opts' with two new fields, 'log_buf'
and 'log_size', allowing users to capture and inspect these log messages.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/lib/bpf/bpf.c | 16 +++++++++++++++-
 tools/lib/bpf/bpf.h |  5 ++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 27845e287dd5c..5b58e981a7669 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -218,7 +218,9 @@ int bpf_map_create(enum bpf_map_type map_type,
 		   const struct bpf_map_create_opts *opts)
 {
 	const size_t attr_sz = offsetofend(union bpf_attr, map_token_fd);
+	struct bpf_common_attr common_attrs;
 	union bpf_attr attr;
+	__u64 log_buf;
 	int fd;
 
 	bump_rlimit_memlock();
@@ -249,7 +251,19 @@ int bpf_map_create(enum bpf_map_type map_type,
 
 	attr.map_token_fd = OPTS_GET(opts, token_fd, 0);
 
-	fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
+	log_buf = (__u64) OPTS_GET(opts, log_buf, NULL);
+	if (log_buf) {
+		if (!feat_supported(NULL, FEAT_EXTENDED_SYSCALL))
+			return libbpf_err(-EOPNOTSUPP);
+
+		memset(&common_attrs, 0, sizeof(common_attrs));
+		common_attrs.log_buf = log_buf;
+		common_attrs.log_size = OPTS_GET(opts, log_size, 0);
+		fd = sys_bpf_extended(BPF_MAP_CREATE, &attr, attr_sz, &common_attrs,
+				      sizeof(common_attrs));
+	} else {
+		fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
+	}
 	return libbpf_err_errno(fd);
 }
 
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 38819071ecbe7..3b54d6feb5842 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -55,9 +55,12 @@ struct bpf_map_create_opts {
 	__s32 value_type_btf_obj_fd;
 
 	__u32 token_fd;
+
+	const char *log_buf;
+	__u32 log_size;
 	size_t :0;
 };
-#define bpf_map_create_opts__last_field token_fd
+#define bpf_map_create_opts__last_field log_size
 
 LIBBPF_API int bpf_map_create(enum bpf_map_type map_type,
 			      const char *map_name,
-- 
2.50.1