On 2/17/23 17:10, Andrii Nakryiko wrote:
On Fri, Feb 17, 2023 at 4:22 PM Kui-Feng Lee <sinquersw@xxxxxxxxx> wrote:
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.
Of course. But I was thinking to move `bpf_map_update_elem(map->fd,
&zero, st_ops->kern_vdata, 0);` part out of bpf_map__update_vdata()
and make update_vdata() just prepare st_ops->kern_vdata only.
Ok! I will rename it as bpf_map_prepare_vdata(), and call
bpf_map_update_elem() separately.
