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Date:   Sun, 12 Jul 2020 22:12:26 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>, Andrey Ignatov <rdna@...com>,
        Takshak Chahande <ctakshak@...com>
Subject: [PATCH bpf-next 3/7] 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@...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

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