The sample bpf program, tcp_rwnd_kern.c, sets the initial
advertized window to 40 packets in an environment where
distinct IPv6 prefixes indicate that both hosts are not
in the same data center.
Signed-off-by: Lawrence Brakmo <bra...@fb.com>
---
samples/bpf/Makefile | 1 +
samples/bpf/tcp_rwnd_kern.c | 55 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 56 insertions(+)
create mode 100644 samples/bpf/tcp_rwnd_kern.c
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 21cb016..9aca209 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -114,6 +114,7 @@ always += xdp_tx_iptunnel_kern.o
always += test_map_in_map_kern.o
always += cookie_uid_helper_example.o
always += tcp_synrto_kern.o
+always += tcp_rwnd_kern.o
HOSTCFLAGS += -I$(objtree)/usr/include
HOSTCFLAGS += -I$(srctree)/tools/lib/
diff --git a/samples/bpf/tcp_rwnd_kern.c b/samples/bpf/tcp_rwnd_kern.c
new file mode 100644
index 0000000..f01b6d4
--- /dev/null
+++ b/samples/bpf/tcp_rwnd_kern.c
@@ -0,0 +1,55 @@
+/*
+ * BPF program to set initial receive window to 40 packets when using IPv6
+ * and the first 5.5 bytes of the IPv6 addresses are not the same (in this
+ * example that means both hosts are not the same datacenter.
+ */
+
+#include <uapi/linux/bpf.h>
+#include <uapi/linux/if_ether.h>
+#include <uapi/linux/if_packet.h>
+#include <uapi/linux/ip.h>
+#include <linux/socket.h>
+#include "bpf_helpers.h"
+
+#define DEBUG 1
+
+SEC("sockops")
+int bpf_rwnd(struct bpf_socket_ops *skops)
+{
+ char fmt1[] = "BPF command: %d\n";
+ char fmt2[] = " Returning %d\n";
+ int rv = -1;
+ int op;
+
+ /* For testing purposes, only execute rest of BPF program
+ * if neither port numberis 55601
+ */
+ if (skops->remote_port != 55601 && skops->local_port != 55601)
+ return -1;
+
+ op = (int) skops->op;
+
+#ifdef DEBUG
+ bpf_trace_printk(fmt1, sizeof(fmt1), op);
+#endif
+
+ /* Check for RWND_INIT operation and IPv6 addresses */
+ if (op == BPF_SOCKET_OPS_RWND_INIT &&
+ skops->family == AF_INET6) {
+
+ /* If the first 5.5 bytes of the IPv6 address are not the same
+ * then both hosts are not in the same datacenter
+ * so use a larger initial advertized window (40 packets)
+ */
+ if (skops->local_ip6[0] != skops->remote_ip6[0] ||
+ (skops->local_ip6[1] & 0xfffff000) !=
+ (skops->remote_ip6[1] & 0xfffff000))
+ bpf_trace_printk(fmt2, sizeof(fmt2), -1);
+ rv = 40;
+ }
+#ifdef DEBUG
+ bpf_trace_printk(fmt2, sizeof(fmt2), rv);
+#endif
+ return rv;
+}
+char _license[] SEC("license") = "GPL";
--
2.9.3
