[PATCH bpf-next v2 5/6] libbpf: Update a bpf_link with another struct_ops.

Kui-Feng Lee
2023-02-23T01:13:09Z

Introduce bpf_link__update_struct_ops(), which will allow you to
effortlessly transition the struct_ops map of any given bpf_link into
an alternative.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
tools/lib/bpf/libbpf.c | 36 ++++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 1 +
tools/lib/bpf/libbpf.map | 2 ++
3 files changed, 39 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 40f239cd1150..0cb3e5ed4d18 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11524,6 +11524,42 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
return &link->link;
}

+/*
+ * Swap the back struct_ops of a link with a new struct_ops map.
+ */
+int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map)
+{
+ struct bpf_link_struct_ops *st_ops_link;
+ __u32 zero = 0;
+ int err, fd;
+
+ if (!bpf_map__is_struct_ops(map) || map->fd == -1)
+ return -EINVAL;
+
+ /* Ensure the type of a link is correct */
+ if (link->detach != bpf_link__detach_struct_ops)
+ return -EINVAL;
+
+ err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
+ if (err) {
+ err = -errno;
+ free(link);
+ return err;
+ }
+
+ fd = bpf_link_update(link->fd, map->fd, NULL);
+ if (fd < 0) {
+ err = -errno;
+ free(link);
+ return err;
+ }
+
+ st_ops_link = container_of(link, struct bpf_link_struct_ops, link);
+ st_ops_link->map_fd = map->fd;
+
+ return 0;
+}
+
typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
void *private_data);

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 2efd80f6f7b9..5e62878d184c 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -695,6 +695,7 @@ bpf_program__attach_freplace(const struct bpf_program *prog,
struct bpf_map;

LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
+LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);

struct bpf_iter_attach_opts {
size_t sz; /* size of this struct for forward/backward compatibility */
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 11c36a3c1a9f..e83571b04c19 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -384,4 +384,6 @@ LIBBPF_1.1.0 {
} LIBBPF_1.0.0;

LIBBPF_1.2.0 {
+ global:
+ bpf_link__update_map;
} LIBBPF_1.1.0;
--
2.30.2