builder/qemu: add use_default_display option

If set, won't set `-display dsl` as a default argument. Useful for osx
compatibility.

builder/qemu/builder.go

@@ -84,30 +84,31 @@ type Config struct {
 	Comm                communicator.Config `mapstructure:",squash"`
 	common.FloppyConfig `mapstructure:",squash"`
 
-	ISOSkipCache    bool       `mapstructure:"iso_skip_cache"`
-	Accelerator     string     `mapstructure:"accelerator"`
-	BootCommand     []string   `mapstructure:"boot_command"`
-	DiskInterface   string     `mapstructure:"disk_interface"`
-	DiskSize        uint       `mapstructure:"disk_size"`
-	DiskCache       string     `mapstructure:"disk_cache"`
-	DiskDiscard     string     `mapstructure:"disk_discard"`
-	SkipCompaction  bool       `mapstructure:"skip_compaction"`
-	DiskCompression bool       `mapstructure:"disk_compression"`
-	Format          string     `mapstructure:"format"`
-	Headless        bool       `mapstructure:"headless"`
-	DiskImage       bool       `mapstructure:"disk_image"`
-	MachineType     string     `mapstructure:"machine_type"`
-	NetDevice       string     `mapstructure:"net_device"`
-	OutputDir       string     `mapstructure:"output_directory"`
-	QemuArgs        [][]string `mapstructure:"qemuargs"`
-	QemuBinary      string     `mapstructure:"qemu_binary"`
-	ShutdownCommand string     `mapstructure:"shutdown_command"`
-	SSHHostPortMin  uint       `mapstructure:"ssh_host_port_min"`
-	SSHHostPortMax  uint       `mapstructure:"ssh_host_port_max"`
-	VNCBindAddress  string     `mapstructure:"vnc_bind_address"`
-	VNCPortMin      uint       `mapstructure:"vnc_port_min"`
-	VNCPortMax      uint       `mapstructure:"vnc_port_max"`
-	VMName          string     `mapstructure:"vm_name"`
+	ISOSkipCache      bool       `mapstructure:"iso_skip_cache"`
+	Accelerator       string     `mapstructure:"accelerator"`
+	BootCommand       []string   `mapstructure:"boot_command"`
+	DiskInterface     string     `mapstructure:"disk_interface"`
+	DiskSize          uint       `mapstructure:"disk_size"`
+	DiskCache         string     `mapstructure:"disk_cache"`
+	DiskDiscard       string     `mapstructure:"disk_discard"`
+	SkipCompaction    bool       `mapstructure:"skip_compaction"`
+	DiskCompression   bool       `mapstructure:"disk_compression"`
+	Format            string     `mapstructure:"format"`
+	Headless          bool       `mapstructure:"headless"`
+	DiskImage         bool       `mapstructure:"disk_image"`
+	MachineType       string     `mapstructure:"machine_type"`
+	NetDevice         string     `mapstructure:"net_device"`
+	OutputDir         string     `mapstructure:"output_directory"`
+	QemuArgs          [][]string `mapstructure:"qemuargs"`
+	QemuBinary        string     `mapstructure:"qemu_binary"`
+	ShutdownCommand   string     `mapstructure:"shutdown_command"`
+	SSHHostPortMin    uint       `mapstructure:"ssh_host_port_min"`
+	SSHHostPortMax    uint       `mapstructure:"ssh_host_port_max"`
+	UseDefaultDisplay bool       `mapstructure:"use_default_display"`
+	VNCBindAddress    string     `mapstructure:"vnc_bind_address"`
+	VNCPortMin        uint       `mapstructure:"vnc_port_min"`
+	VNCPortMax        uint       `mapstructure:"vnc_port_max"`
+	VMName            string     `mapstructure:"vm_name"`
 
 	// These are deprecated, but we keep them around for BC
 	// TODO(@mitchellh): remove

builder/qemu/step_run.go

@@ -124,7 +124,9 @@ func getCommandArgs(bootDrive string, state multistep.StateBag) ([]string, error
 		}
 	} else {
 		if qemuMajor >= 2 {
-			defaultArgs["-display"] = "sdl"
+			if !config.UseDefaultDisplay {
+				defaultArgs["-display"] = "sdl"
+			}
 		} else {
 			ui.Message("WARNING: The version of qemu  on your host doesn't support display mode.\n" +
 				"The display parameter will be ignored.")

website/source/docs/builders/qemu.html.md

@@ -236,6 +236,10 @@ Linux server and have not enabled X11 forwarding (`ssh -X`).
     switch/value pairs. Any value specified as an empty string is ignored. All
     values after the switch are concatenated with no separator.
 
+-   `use_default_display` (boolean) - If true, do not pass a `-display` option
+    to qemu, allowing it to choose the default. This may be needed when running
+    under OS X.
+
 \~> **Warning:** The qemu command line allows extreme flexibility, so beware
 of conflicting arguments causing failures of your run. For instance, using
 --no-acpi could break the ability to send power signal type commands (e.g.,