From d237c92273e2b1b38331a2b9b9c81e1d2efd2a4d Mon Sep 17 00:00:00 2001
From: Tycho Andersen <tycho@docker.com>
Date: Thu, 20 Jul 2017 12:36:07 -0600
Subject: [PATCH] support tap devices in qemu backend

The motivation for this is networking out (in particular, testing NFS
support) from the VM.

We could be a lot more user friendly (a la libvirt) by creating the tap
device for users and allowing them to specify a bridge instead, but then
we'd need root to create this tap device. For now, let's make people do
their own tap devices, and just use them. A tap device can be created for a
bridge as follows:

    # ip tuntap add linuxkit0 mode tap user `whoami`
    # ip link set linuxkit0 up
    # ip link set linuxkit0 master $bridge_name

and then used by:

    $ ./bin/linuxkit run qemu -tap-device linuxkit0 linuxkit

Signed-off-by: Tycho Andersen <tycho@docker.com>
---
 src/cmd/linuxkit/run_qemu.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/cmd/linuxkit/run_qemu.go b/src/cmd/linuxkit/run_qemu.go
index 210faa630..618d84e84 100644
--- a/src/cmd/linuxkit/run_qemu.go
+++ b/src/cmd/linuxkit/run_qemu.go
@@ -35,6 +35,7 @@ type QemuConfig struct {
 	QemuBinPath    string
 	QemuImgPath    string
 	PublishedPorts []string
+	TapDevice      string
 }
 
 func haveKVM() bool {
@@ -96,6 +97,7 @@ func runQemu(args []string) {
 
 	publishFlags := multipleFlag{}
 	flags.Var(&publishFlags, "publish", "Publish a vm's port(s) to the host (default [])")
+	tapDevice := flags.String("tap-device", "", "Tap device to use as eth0 (optional)")
 
 	if err := flags.Parse(args); err != nil {
 		log.Fatal("Unable to parse args")
@@ -215,6 +217,7 @@ func runQemu(args []string) {
 		KVM:            *enableKVM,
 		Containerized:  *qemuContainerized,
 		PublishedPorts: publishFlags,
+		TapDevice:      *tapDevice,
 	}
 
 	config = discoverBackend(config)
@@ -447,6 +450,12 @@ func buildQemuCmdline(config QemuConfig) (QemuConfig, []string) {
 		qemuArgs = append(qemuArgs, "-net", "nic")
 	}
 
+	if config.TapDevice != "" {
+		qemuArgs = append(qemuArgs, "-net", "nic,model=virtio")
+		tapArg := fmt.Sprintf("tap,ifname=%s,script=no,downscript=no", config.TapDevice)
+		qemuArgs = append(qemuArgs, "-net", tapArg)
+	}
+
 	if config.GUI != true {
 		qemuArgs = append(qemuArgs, "-nographic")
 	}