From 08270b18aa1bd815b7109f08501a5adc1df189d2 Mon Sep 17 00:00:00 2001
From: Justin Cormack <justin.cormack@docker.com>
Date: Thu, 5 Jan 2017 23:22:59 +0000
Subject: [PATCH] Add the MTU script for dhcpcd

This might fix the issue that GCE is not setting the MTU from
the DHCP response. The documentation says this is shipped but
it is not in Alpine, this one is from a NetBSD install.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>
---
 alpine/usr/lib/dhcpcd/dhcpcd-hooks/10-mtu | 38 +++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 alpine/usr/lib/dhcpcd/dhcpcd-hooks/10-mtu

diff --git a/alpine/usr/lib/dhcpcd/dhcpcd-hooks/10-mtu b/alpine/usr/lib/dhcpcd/dhcpcd-hooks/10-mtu
new file mode 100644
index 000000000..f04274e70
--- /dev/null
+++ b/alpine/usr/lib/dhcpcd/dhcpcd-hooks/10-mtu
@@ -0,0 +1,38 @@
+# Configure the MTU for the interface
+
+mtu_dir="$state_dir/mtu"
+
+set_mtu()
+{
+	local mtu=$1
+
+	if [ -w /sys/class/net/$interface/mtu ]; then
+		echo "$mtu" >/sys/class/net/$interface/mtu
+	else
+		ifconfig "$interface" mtu "$mtu"
+	fi
+}
+
+if [ "$reason" = PREINIT -a -e "$mtu_dir/$interface" ]; then
+	rm "$mtu_dir/$interface"
+elif [ -n "$new_interface_mtu" ] && $if_up; then
+	# The smalled MTU dhcpcd can work with is 576
+	if [ "$new_interface_mtu" -ge 576 ]; then
+		if set_mtu "$new_interface_mtu"; then
+			syslog info "$interface: MTU set to $new_interface_mtu"
+			# Save the MTU so we can restore it later
+			if [ ! -e "$mtu_dir/$interface" ]; then
+				mkdir -p "$mtu_dir"
+				echo "$ifmtu" > "$mtu_dir/$interface"
+			fi
+		fi
+	fi
+elif [ -e "$mtu_dir/$interface" ]; then
+	if $if_up || $if_down; then
+		# No MTU in this state, so restore the prior MTU
+		mtu=$(cat "$mtu_dir/$interface")
+		syslog info "$interface: MTU restored to $mtu"
+		set_mtu "$mtu"
+		rm "$mtu_dir/$interface"
+	fi
+fi