On 2/16/23 14:48, Andrii Nakryiko wrote:
On Tue, Feb 14, 2023 at 2:17 PM Kui-Feng Lee <kuifeng@xxxxxxxx> wrote:
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@xxxxxxxx>
---
tools/lib/bpf/libbpf.c | 35 +++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 1 +
tools/lib/bpf/libbpf.map | 1 +
3 files changed, 37 insertions(+)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 1eff6a03ddd9..6f7c72e312d4 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11524,6 +11524,41 @@ 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_struct_ops(struct bpf_link *link, const struct bpf_map *map)
we have bpf_link__update_program(), and so the generic counterpart for
map-based links would be bpf_link__update_map(). Let's call it that.
And it shouldn't probably assume so much struct_ops specific things.
Sure
+{
+ struct bpf_link_struct_ops_map *st_ops_link;
+ 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_vdata(map);
it's a bit weird we do this at attach time, not when bpf_map is
actually instantiated. Should we move this map contents initialization
to bpf_object__load() phase? Same for bpf_map__attach_struct_ops().
What do we lose by doing it after all the BPF programs are loaded in
load phase?
With the current behavior (w/o links), a struct_ops will be registered
when updating its value. If we move bpf_map__update_vdata() to
bpf_object__load(), a congestion control algorithm will be activated at
the moment loading it before attaching it. However, we should activate
an algorithm at attach time.
+ 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_map, 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..dd25cd6759d4 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_struct_ops(struct bpf_link *link, const struct bpf_map *map);
let's rename to bpf_link__update_map() and put it next to
bpf_link__update_program() in libbpf.h
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..ca6993c744b6 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -373,6 +373,7 @@ LIBBPF_1.1.0 {
global:
bpf_btf_get_fd_by_id_opts;
bpf_link_get_fd_by_id_opts;
+ bpf_link__update_struct_ops;
bpf_map_get_fd_by_id_opts;
bpf_prog_get_fd_by_id_opts;
user_ring_buffer__discard;
we are in LIBBPF_1.2.0 already, please move
--
2.30.2
