On 2026/1/16 09:03, Andrii Nakryiko wrote:

On Mon, Jan 12, 2026 at 6:59 AM Leon Hwang [off-list ref] wrote:

quoted

With the previous commit adding common attribute support for
BPF_MAP_CREATE, users can now retrieve detailed error messages when map
creation fails via the log_buf field.

Introduce struct bpf_syscall_common_attr_opts with the following fields:
log_buf, log_size, log_level, and log_true_size.

Extend bpf_map_create_opts with a new field common_attr_opts, allowing
users to capture and inspect log messages on map creation failures.

Signed-off-by: Leon Hwang <redacted>
---
 tools/lib/bpf/bpf.c | 15 ++++++++++++++-
 tools/lib/bpf/bpf.h | 17 ++++++++++++++++-
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index d44e667aaf02..d65df1b7b2be 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c

@@ -207,6 +207,9 @@ 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, excl_prog_hash_size);
+       const size_t common_attr_sz = sizeof(struct bpf_common_attr);
+       struct bpf_syscall_common_attr_opts *common_attr_opts;
+       struct bpf_common_attr common_attr;
        union bpf_attr attr;
        int fd;

@@ -240,7 +243,17 @@ int bpf_map_create(enum bpf_map_type map_type,
        attr.excl_prog_hash = ptr_to_u64(OPTS_GET(opts, excl_prog_hash, NULL));
        attr.excl_prog_hash_size = OPTS_GET(opts, excl_prog_hash_size, 0);

-       fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
+       common_attr_opts = OPTS_GET(opts, common_attr_opts, NULL);
+       if (common_attr_opts && feat_supported(NULL, FEAT_EXTENDED_SYSCALL)) {
+               memset(&common_attr, 0, common_attr_sz);
+               common_attr.log_buf = ptr_to_u64(OPTS_GET(common_attr_opts, log_buf, NULL));
+               common_attr.log_size = OPTS_GET(common_attr_opts, log_size, 0);
+               common_attr.log_level = OPTS_GET(common_attr_opts, log_level, 0);
+               fd = sys_bpf_ext_fd(BPF_MAP_CREATE, &attr, attr_sz, &common_attr, common_attr_sz);
+               OPTS_SET(common_attr_opts, log_true_size, common_attr.log_true_size);
+       } else {
+               fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);

OPTS_SET(log_true_size) to zero here, maybe?

Unnecessary, but ok to do it.

quoted

+       }
        return libbpf_err_errno(fd);
 }

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 2c8e88ddb674..c4a26e6b71ea 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h

@@ -37,6 +37,18 @@ extern "C" {

 LIBBPF_API int libbpf_set_memlock_rlim(size_t memlock_bytes);

+struct bpf_syscall_common_attr_opts {
+       size_t sz; /* size of this struct for forward/backward compatibility */
+
+       char *log_buf;
+       __u32 log_size;
+       __u32 log_level;
+       __u32 log_true_size;
+
+       size_t :0;
+};
+#define bpf_syscall_common_attr_opts__last_field log_true_size

see below, let's drop this struct and just add these 4 fields directly
to bpf_map_create_opts

quoted

+
 struct bpf_map_create_opts {
        size_t sz; /* size of this struct for forward/backward compatibility */

@@ -57,9 +69,12 @@ struct bpf_map_create_opts {

        const void *excl_prog_hash;
        __u32 excl_prog_hash_size;
+
+       struct bpf_syscall_common_attr_opts *common_attr_opts;

maybe let's just add those log_xxx fields here directly? This whole
extra bpf_syscall_common_attr_opts pointer and struct seems like a
cumbersome API.

Oops... This struct was suggested by the v3 discussion [1].

This struct was used to report 'log_true_size' without changing
'bpf_map_create()' API.

Links
[1]
https://lore.kernel.org/bpf/CAEf4Bzaw9cboFSf1OXmD84S7pKaeyj=bcQg_diUzGwAkFsjUgg@mail.gmail.com/ (local)

Thanks,
Leon

quoted

+
        size_t :0;
 };
-#define bpf_map_create_opts__last_field excl_prog_hash_size
+#define bpf_map_create_opts__last_field common_attr_opts

 LIBBPF_API int bpf_map_create(enum bpf_map_type map_type,
                              const char *map_name,
--
2.52.0