Provide a common share between VMs to allow easy communication

Every VM now mounts a common SMB share on /tmp/shared.

lib/test-driver/Machine.pm

@@ -8,10 +8,13 @@ use POSIX qw(dup2);
 use FileHandle;
 use Cwd;
 use File::Basename;
+use File::Path qw(make_path);
 
 
 my $showGraphics = defined $ENV{'DISPLAY'};
 
+my $sharedDir;
+
 
 sub new {
     my ($class, $args) = @_;
@@ -40,7 +43,11 @@ sub new {
     }
 
     my $tmpDir = $ENV{'TMPDIR'} || "/tmp";
-    
+    unless (defined $sharedDir) {
+        $sharedDir = $tmpDir . "/xchg-shared";
+        make_path($sharedDir, { mode => 0700, owner => $< });
+    }
+
     my $self = {
         startCommand => $startCommand,
         name => $name,
@@ -123,6 +130,7 @@ sub start {
         dup2(fileno($serialC), fileno(STDOUT));
         dup2(fileno($serialC), fileno(STDERR));
         $ENV{TMPDIR} = $self->{stateDir};
+        $ENV{SHARED_DIR} = $sharedDir;
         $ENV{USE_TMPDIR} = 1;
         $ENV{QEMU_OPTS} =
             "-no-reboot -monitor unix:./monitor -chardev socket,id=shell,path=./shell " .

modules/virtualisation/qemu-vm.nix

@@ -155,6 +155,14 @@ let
       cd $TMPDIR
       mkdir -p $TMPDIR/xchg
 
+      EXTRA_SAMBA_CONF="
+        [shared]
+          force user = $WHO
+          path = ''${SHARED_DIR:-$TMPDIR/xchg}
+          read only = no
+          guest ok = yes
+      "
+
       ${pkgs.vmTools.startSamba}
 
       # Start QEMU.
@@ -328,6 +336,12 @@ in
         options = "guest,sec=none,noperm,noacl";
         neededForBoot = true;
       }
+      { mountPoint = "/tmp/shared";
+        device = "//10.0.2.4/shared";
+        fsType = "cifs";
+        options = "guest,sec=none,noperm,noacl";
+        neededForBoot = true;
+      }
     ] ++ optional cfg.useBootLoader
       { mountPoint = "/boot";
         device = "/dev/disk/by-label/boot";