[PATCH bpf-next 4/5] libbpf: add the function libbpf_find_kernel_btf_id()

Menglong Dong
2024-02-20T03:51:30Z

Add new function libbpf_find_kernel_btf_id() to find the btf type id of
the kernel, including vmlinux and modules.

Signed-off-by: Menglong Dong <dongmenglong.8@bytedance.com>
---
tools/lib/bpf/libbpf.c | 83 ++++++++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 3 ++
tools/lib/bpf/libbpf.map | 1 +
3 files changed, 87 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 01f407591a92..44e34007de8c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9500,6 +9500,89 @@ int libbpf_find_vmlinux_btf_id(const char *name,
return libbpf_err(err);
}

+int libbpf_find_kernel_btf_id(const char *name,
+ enum bpf_attach_type attach_type,
+ int *btf_obj_fd, int *btf_type_id)
+{
+ struct btf *btf, *vmlinux_btf;
+ struct bpf_btf_info info;
+ __u32 btf_id = 0, len;
+ char btf_name[64];
+ int err, fd;
+
+ vmlinux_btf = btf__load_vmlinux_btf();
+ err = libbpf_get_error(vmlinux_btf);
+ if (err)
+ return libbpf_err(err);
+
+ err = find_attach_btf_id(vmlinux_btf, name, attach_type);
+ if (err > 0) {
+ *btf_type_id = err;
+ *btf_obj_fd = 0;
+ err = 0;
+ goto out;
+ }
+
+ /* kernel too old to support module BTFs */
+ if (!feat_supported(NULL, FEAT_MODULE_BTF)) {
+ err = -EOPNOTSUPP;
+ goto out;
+ }
+
+ while (true) {
+ err = bpf_btf_get_next_id(btf_id, &btf_id);
+ if (err) {
+ err = -errno;
+ goto out;
+ }
+
+ fd = bpf_btf_get_fd_by_id(btf_id);
+ if (fd < 0) {
+ if (errno == ENOENT)
+ continue;
+ err = -errno;
+ goto out;
+ }
+
+ len = sizeof(info);
+ memset(&info, 0, sizeof(info));
+ info.name = ptr_to_u64(btf_name);
+ info.name_len = sizeof(btf_name);
+
+ err = bpf_btf_get_info_by_fd(fd, &info, &len);
+ if (err) {
+ err = -errno;
+ goto fd_out;
+ }
+
+ if (!info.kernel_btf || strcmp(btf_name, "vmlinux") == 0) {
+ close(fd);
+ continue;
+ }
+
+ btf = btf_get_from_fd(fd, vmlinux_btf);
+ err = libbpf_get_error(btf);
+ if (err)
+ goto fd_out;
+
+ err = find_attach_btf_id(btf, name, attach_type);
+ if (err > 0) {
+ *btf_type_id = err;
+ *btf_obj_fd = fd;
+ err = 0;
+ break;
+ }
+ close(fd);
+ continue;
+fd_out:
+ close(fd);
+ break;
+ }
+out:
+ btf__free(vmlinux_btf);
+ return err;
+}
+
static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
{
struct bpf_prog_info info;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 5723cbbfcc41..ca151bbec833 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -306,6 +306,9 @@ LIBBPF_API int libbpf_attach_type_by_name(const char *name,
enum bpf_attach_type *attach_type);
LIBBPF_API int libbpf_find_vmlinux_btf_id(const char *name,
enum bpf_attach_type attach_type);
+LIBBPF_API int libbpf_find_kernel_btf_id(const char *name,
+ enum bpf_attach_type attach_type,
+ int *btf_obj_fd, int *btf_type_id);

/* Accessors of bpf_program */
struct bpf_program;
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 86804fd90dd1..73c60f47b4bb 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -413,4 +413,5 @@ LIBBPF_1.4.0 {
bpf_token_create;
btf__new_split;
btf_ext__raw_data;
+ libbpf_find_kernel_btf_id;
} LIBBPF_1.3.0;
--
2.39.2