launch: Treat /dev/null specially, for old KVM.

Old KVM can't add /dev/null readonly.  Treat /dev/null as a special
case.

We also fix a few tests where /dev/null was being used with
format=qcow2.  This was always incorrect behaviour, but qemu appears
to tolerate it.

2 files changed, 10 insertions, 2 deletions

diff --git a/python/t/060-optargs.py b/python/t/060-optargs.py
index 75ea06f3..be28a3ce 100644
--- a/python/t/060-optargs.py
+++ b/python/t/060-optargs.py
@@ -21,5 +21,5 @@ import guestfs
 g = guestfs.GuestFS()
 g.add_drive_opts ("/dev/null")
 g.add_drive_opts ("/dev/null", readonly = 1)
-g.add_drive_opts ("/dev/null", iface = "virtio", format = "qcow2")
+g.add_drive_opts ("/dev/null", iface = "virtio", format = "raw")
 g.close ()
diff --git a/python/t/rhbz811650.py b/python/t/rhbz811650.py
index 84daf0fe..cf01673f 100644
--- a/python/t/rhbz811650.py
+++ b/python/t/rhbz811650.py
@@ -15,11 +15,17 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
+import os
 import guestfs
 
+f = open ("test.img", "w")
+f.truncate (500 * 1024 * 1024)
+f.close ()
+
 g = guestfs.GuestFS ()
 
-g.add_drive_opts ("/dev/null", format="qcow2");
+# Deliberate error: the disk format is supposed to be raw.
+g.add_drive_opts ("test.img", format="qcow2");
 
 # Because error() wasn't being called, guestfs_last_error would return
 # NULL, causing a segfault in the Python bindings (RHBZ#811650).
@@ -27,3 +33,5 @@ try:
     g.launch ()
 except:
     pass
+
+os.unlink ("test.img")