Add multidevs option to fsdev

multidevs specifies how to deal with multiple devices being shared with a 9p
export. `multidevs=remap` fixes the following warning:

```
9p: Multiple devices detected in same VirtFS export, which might lead to file
ID collisions and severe misbehaviours on guest!
You should either use a separate export for each device shared from host or
use virtfs option 'multidevs=remap'!
```

Signed-off-by: Julio Montes <julio.montes@intel.com>

qemu/qemu.go

@@ -288,6 +288,23 @@ func (object Object) QemuParams(config *Config) []string {
 	return qemuParams
 }
 
+// Virtio9PMultidev filesystem behaviour to deal
+// with multiple devices being shared with a 9p export.
+type Virtio9PMultidev string
+
+const (
+	// Remap shares multiple devices with only one export.
+	Remap Virtio9PMultidev = "remap"
+
+	// Warn assumes that only one device is shared by the same export.
+	// Only a warning message is logged (once) by qemu on host side.
+	// This is the default behaviour.
+	Warn Virtio9PMultidev = "warn"
+
+	// Forbid like "warn" but also deny access to additional devices on guest.
+	Forbid Virtio9PMultidev = "forbid"
+)
+
 // FSDriver represents a qemu filesystem driver.
 type FSDriver string
 
@@ -350,6 +367,10 @@ type FSDevice struct {
 
 	// Transport is the virtio transport for this device.
 	Transport VirtioTransport
+
+	// Multidev is the filesystem behaviour to deal
+	// with multiple devices being shared with a 9p export
+	Multidev Virtio9PMultidev
 }
 
 // Virtio9PTransport is a map of the virtio-9p device name that corresponds
@@ -393,6 +414,10 @@ func (fsdev FSDevice) QemuParams(config *Config) []string {
 	fsParams = append(fsParams, fmt.Sprintf(",path=%s", fsdev.Path))
 	fsParams = append(fsParams, fmt.Sprintf(",security_model=%s", fsdev.SecurityModel))
 
+	if fsdev.Multidev != "" {
+		fsParams = append(fsParams, fmt.Sprintf(",multidevs=%s", fsdev.Multidev))
+	}
+
 	qemuParams = append(qemuParams, "-device")
 	qemuParams = append(qemuParams, strings.Join(deviceParams, ""))
 

qemu/qemu_arch_base_test.go

@@ -21,7 +21,7 @@ package qemu
 import "testing"
 
 var (
-	deviceFSString                 = "-device virtio-9p-pci,disable-modern=true,fsdev=workload9p,mount_tag=rootfs,romfile=efi-virtio.rom -fsdev local,id=workload9p,path=/var/lib/docker/devicemapper/mnt/e31ebda2,security_model=none"
+	deviceFSString                 = "-device virtio-9p-pci,disable-modern=true,fsdev=workload9p,mount_tag=rootfs,romfile=efi-virtio.rom -fsdev local,id=workload9p,path=/var/lib/docker/devicemapper/mnt/e31ebda2,security_model=none,multidevs=remap"
 	deviceNetworkString            = "-netdev tap,id=tap0,vhost=on,ifname=ceth0,downscript=no,script=no -device driver=virtio-net-pci,netdev=tap0,mac=01:02:de:ad:be:ef,disable-modern=true,romfile=efi-virtio.rom"
 	deviceNetworkStringMq          = "-netdev tap,id=tap0,vhost=on,fds=3:4 -device driver=virtio-net-pci,netdev=tap0,mac=01:02:de:ad:be:ef,disable-modern=true,mq=on,vectors=6,romfile=efi-virtio.rom"
 	deviceSerialString             = "-device virtio-serial-pci,disable-modern=true,id=serial0,romfile=efi-virtio.rom,max_ports=2"

qemu/qemu_s390x_test.go

@@ -23,7 +23,7 @@ import "testing"
 // -pci devices don't play well with Z hence replace them with corresponding -ccw devices
 // See https://wiki.qemu.org/Documentation/Platforms/S390X
 var (
-	deviceFSString                 = "-device virtio-9p-ccw,fsdev=workload9p,mount_tag=rootfs,devno=" + DevNo + " -fsdev local,id=workload9p,path=/var/lib/docker/devicemapper/mnt/e31ebda2,security_model=none"
+	deviceFSString                 = "-device virtio-9p-ccw,fsdev=workload9p,mount_tag=rootfs,devno=" + DevNo + " -fsdev local,id=workload9p,path=/var/lib/docker/devicemapper/mnt/e31ebda2,security_model=none,multidevs=remap"
 	deviceNetworkString            = "-netdev tap,id=tap0,vhost=on,ifname=ceth0,downscript=no,script=no -device driver=virtio-net-ccw,netdev=tap0,mac=01:02:de:ad:be:ef,devno=" + DevNo
 	deviceNetworkStringMq          = "-netdev tap,id=tap0,vhost=on,fds=3:4 -device driver=virtio-net-ccw,netdev=tap0,mac=01:02:de:ad:be:ef,mq=on,devno=" + DevNo
 	deviceSerialString             = "-device virtio-serial-ccw,id=serial0,devno=" + DevNo

qemu/qemu_test.go

@@ -149,6 +149,7 @@ func TestAppendDeviceFS(t *testing.T) {
 		SecurityModel: None,
 		DisableModern: true,
 		ROMFile:       "efi-virtio.rom",
+		Multidev:      Remap,
 	}
 
 	if fsdev.Transport.isVirtioCCW(nil) {