[PATCH v2 5/6] libbpf: Introduce bpf_link_get_fd_by_id_opts()

Roberto Sassu
2022-10-06T11:09:19Z

Introduce bpf_link_get_fd_by_id_opts(), for symmetry with
bpf_map_get_fd_by_id_opts(), to let the caller pass the newly introduced
data structure bpf_get_fd_by_id_opts. Keep the existing
bpf_link_get_fd_by_id(), and call bpf_link_get_fd_by_id_opts() with NULL as
opts argument, to prevent setting open_flags.

Currently, the kernel does not support non-zero open_flags for
bpf_link_get_fd_by_id_opts(), and a call with them will result in an error
returned by the bpf() system call. The caller should always pass zero
open_flags.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
tools/lib/bpf/bpf.c | 12 +++++++++++-
tools/lib/bpf/bpf.h | 2 ++
tools/lib/bpf/libbpf.map | 1 +
3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index b95fed0c1644..9aff98f42a3d 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -1004,19 +1004,29 @@ int bpf_btf_get_fd_by_id(__u32 id)
return bpf_btf_get_fd_by_id_opts(id, NULL);
}

-int bpf_link_get_fd_by_id(__u32 id)
+int bpf_link_get_fd_by_id_opts(__u32 id,
+ const struct bpf_get_fd_by_id_opts *opts)
{
const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
union bpf_attr attr;
int fd;

+ if (!OPTS_VALID(opts, bpf_get_fd_by_id_opts))
+ return libbpf_err(-EINVAL);
+
memset(&attr, 0, attr_sz);
attr.link_id = id;
+ attr.open_flags = OPTS_GET(opts, open_flags, 0);

fd = sys_bpf_fd(BPF_LINK_GET_FD_BY_ID, &attr, attr_sz);
return libbpf_err_errno(fd);
}

+int bpf_link_get_fd_by_id(__u32 id)
+{
+ return bpf_link_get_fd_by_id_opts(id, NULL);
+}
+
int bpf_obj_get_info_by_fd(int bpf_fd, void *info, __u32 *info_len)
{
const size_t attr_sz = offsetofend(union bpf_attr, info);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 4b487305eeb8..a112e0ed1b19 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -383,6 +383,8 @@ LIBBPF_API int bpf_btf_get_fd_by_id(__u32 id);
LIBBPF_API int bpf_btf_get_fd_by_id_opts(__u32 id,
const struct bpf_get_fd_by_id_opts *opts);
LIBBPF_API int bpf_link_get_fd_by_id(__u32 id);
+LIBBPF_API int bpf_link_get_fd_by_id_opts(__u32 id,
+ const struct bpf_get_fd_by_id_opts *opts);
LIBBPF_API int bpf_obj_get_info_by_fd(int bpf_fd, void *info, __u32 *info_len);

struct bpf_prog_query_opts {
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 7011d5eec67b..71bf5691a689 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -372,6 +372,7 @@ LIBBPF_1.0.0 {
LIBBPF_1.1.0 {
global:
bpf_btf_get_fd_by_id_opts;
+ bpf_link_get_fd_by_id_opts;
bpf_map_get_fd_by_id_opts;
bpf_prog_get_fd_by_id_opts;
user_ring_buffer__discard;
--
2.25.1