[Libguestfs] [PATCH libnbd 2/4] lib: Implement TCP fastopen

[Richard W.M. Jones]

We use the simpler (Linux only) implementation where you just set the
TCP_FASTOPEN_CONNECT socket option.  The alternative method of using
sendmsg + MSG_FASTOPEN requires more complicated userspace changes.
---
 generator/states-connect.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/generator/states-connect.c b/generator/states-connect.c
index 07d4e234e..00d771d3a 100644
--- a/generator/states-connect.c
+++ b/generator/states-connect.c
@@ -63,6 +63,23 @@ disable_sigpipe (int sock)
 #endif
 }
 
+/* Set TCP fastopen (TFO) on connect if supported, but don't fail. */
+static void
+set_tcp_fastopen (struct nbd_handle *h, int family, int sock)
+{
+#ifdef TCP_FASTOPEN_CONNECT
+  const int flag = 1;
+
+  if (!h->fastopen) return;
+  if (family != AF_INET && family != AF_INET6) return;
+
+  if (setsockopt (sock, IPPROTO_TCP, TCP_FASTOPEN_CONNECT,
+                  &flag, sizeof flag) == -1)
+    debug (h, "ignoring error trying to request TCP fastopen: %s",
+           strerror (errno));
+#endif /* TCP_FASTOPEN_CONNECT */
+}
+
 STATE_MACHINE {
  CONNECT.START:
   sa_family_t family;
@@ -84,6 +101,7 @@  CONNECT.START:
 
   disable_nagle (fd);
   disable_sigpipe (fd);
+  set_tcp_fastopen (h, family, fd);
 
   r = connect (fd, (struct sockaddr *)&h->connaddr, h->connaddrlen);
   if (r == 0 || (r == -1 && errno == EINPROGRESS))
@@ -197,6 +215,7 @@  CONNECT_TCP.CONNECT:
 
   disable_nagle (fd);
   disable_sigpipe (fd);
+  set_tcp_fastopen (h, h->rp->ai_family, fd);
 
   if (connect (fd, h->rp->ai_addr, h->rp->ai_addrlen) == -1) {
     if (errno != EINPROGRESS) {
-- 
2.46.0
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