bpf, xdp: Implement LINK_UPDATE for BPF XDP link

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

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200722064603.3350758-6-andriin@fb.com

diff --git a/net/core/dev.c b/net/core/dev.c
index e24248f..49f284f 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8996,9 +8996,52 @@ 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)