[PATCH bpf-next 3/7] bpf, xdp: implement LINK_UPDATE for BPF XDP link

[Andrii Nakryiko]

Add support for LINK_UPDATE command for BPF XDP link to enable reliable
replacement of underlying BPF program.

Signed-off-by: Andrii Nakryiko <andr...@fb.com>
---
 net/core/dev.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 84f755a1ec36..025687120442 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8973,9 +8973,52 @@ static void bpf_xdp_link_dealloc(struct bpf_link *link)
        kfree(xdp_link);
 }
 
+static int bpf_xdp_link_update(struct bpf_link *link, struct bpf_prog 
*new_prog,
+                              struct bpf_prog *old_prog)
+{
+       struct bpf_xdp_link *xdp_link = container_of(link, struct bpf_xdp_link, 
link);
+       enum bpf_xdp_mode mode;
+       bpf_op_t bpf_op;
+       int err = 0;
+
+       rtnl_lock();
+
+       /* link might have been auto-released already, so fail */
+       if (!xdp_link->dev) {
+               err = -ENOLINK;
+               goto out_unlock;
+       }
+
+       if (old_prog && link->prog != old_prog) {
+               err = -EPERM;
+               goto out_unlock;
+       }
+       old_prog = link->prog;
+       if (old_prog == new_prog) {
+               /* no-op, don't disturb drivers */
+               bpf_prog_put(new_prog);
+               goto out_unlock;
+       }
+
+       mode = dev_xdp_mode(xdp_link->flags);
+       bpf_op = dev_xdp_bpf_op(xdp_link->dev, mode);
+       err = dev_xdp_install(xdp_link->dev, mode, bpf_op, NULL,
+                             xdp_link->flags, new_prog);
+       if (err)
+               goto out_unlock;
+
+       old_prog = xchg(&link->prog, new_prog);
+       bpf_prog_put(old_prog);
+
+out_unlock:
+       rtnl_unlock();
+       return err;
+}
+
 static const struct bpf_link_ops bpf_xdp_link_lops = {
        .release = bpf_xdp_link_release,
        .dealloc = bpf_xdp_link_dealloc,
+       .update_prog = bpf_xdp_link_update,
 };
 
 int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
-- 
2.24.1