[RFC,v3,06/15] libbpf: Introduce bpf_link_get_fd_by_id_opts()

Commit Message

Roberto Sassu July 22, 2022, 5:18 p.m. UTC

Introduce bpf_link_get_fd_by_id_opts(), to let the caller specify the
needed permissions for the operation. Keep the existing
bpf_link_get_fd_by_id(), to request read-write permissions.

Currently, setting permissions in the data structure has no effect, as the
kernel does not evaluate them. The new variant has been introduced anyway
for symmetry with bpf_map_get_fd_by_id_opts(). Evaluating permissions could
be done in future kernel versions.

Signed-off-by: Roberto Sassu <[e-mail]>
---
 tools/lib/bpf/bpf.c      | 13 ++++++++++++-
 tools/lib/bpf/bpf.h      |  2 ++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 15 insertions(+), 1 deletion(-)

Patch

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index b131bbc8509e..5f2785a4c358 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -1002,18 +1002,29 @@  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_opts *opts)
 {
 	union bpf_attr attr;
 	int fd;
 
+	if (!OPTS_VALID(opts, bpf_get_fd_opts))
+		return libbpf_err(-EINVAL);
+
 	memset(&attr, 0, sizeof(attr));
 	attr.link_id = id;
+	if (kernel_supports(NULL, FEAT_GET_FD_BY_ID_OPEN_FLAGS))
+		attr.open_flags = OPTS_GET(opts, flags, 0);
 
 	fd = sys_bpf_fd(BPF_LINK_GET_FD_BY_ID, &attr, sizeof(attr));
 	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)
 {
 	union bpf_attr attr;
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 45d3739d901f..b75fd9d37bad 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -372,6 +372,8 @@  LIBBPF_API int bpf_map_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_btf_get_fd_by_id_opts(__u32 id,
 					 const struct bpf_get_fd_opts *opts);
 LIBBPF_API int bpf_btf_get_fd_by_id(__u32 id);
+LIBBPF_API int bpf_link_get_fd_by_id_opts(__u32 id,
+					  const struct bpf_get_fd_opts *opts);
 LIBBPF_API int bpf_link_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_obj_get_info_by_fd(int bpf_fd, void *info, __u32 *info_len);
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index ee6755dbf004..dba97d2ef8a9 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -367,4 +367,5 @@  LIBBPF_1.0.0 {
 		bpf_prog_get_fd_by_id_opts;
 		bpf_map_get_fd_by_id_opts;
 		bpf_btf_get_fd_by_id_opts;
+		bpf_link_get_fd_by_id_opts;
 };