dom0+vm: qvm-block --attach-file

Allow to attach disk image from different VM as block device. File attached
with qvm-block -A will be visible as loopX device and as such can be detached.
File path will be in device description.

dom0/qvm-core/qubesutils.py

@@ -142,6 +142,9 @@ def block_name_to_majorminor(name):
     elif name.startswith("sr"):
         disk = False
         major = 11
+    elif name.startswith("loop"):
+        disk = False
+        major = 7
     elif name.startswith("md"):
         disk = False
         major = 9
@@ -242,25 +245,34 @@ def block_check_attached(backend_vm, device, backend_xid = None):
     vm_list = xs.ls('', '/local/domain/%d/backend/vbd' % backend_xid)
     if vm_list is None:
         return None
-    device_majorminor = block_name_to_majorminor(device)
+    device_majorminor = None
+    try:
+        device_majorminor = block_name_to_majorminor(device)
+    except:
+        # Unknown devices will be compared directly - perhaps it is a filename?
+        pass
     for vm_xid in vm_list:
         for devid in xs.ls('', '/local/domain/%d/backend/vbd/%s' % (backend_xid, vm_xid)):
             (tmp_major, tmp_minor) = (0, 0)
             phys_device = xs.read('', '/local/domain/%d/backend/vbd/%s/%s/physical-device' % (backend_xid, vm_xid, devid))
+            dev_params = xs.read('', '/local/domain/%d/backend/vbd/%s/%s/params' % (backend_xid, vm_xid, devid))
             if phys_device and phys_device.find(':'):
                 (tmp_major, tmp_minor) = phys_device.split(":")
                 tmp_major = int(tmp_major, 16)
                 tmp_minor = int(tmp_minor, 16)
             else:
                 # perhaps not ready yet - check params
-                dev_params = xs.read('', '/local/domain/%d/backend/vbd/%s/%s/params' % (backend_xid, vm_xid, devid))
+                if not dev_params:
-                if not dev_params or not dev_params.startswith('/dev/'):
                     # Skip not-phy devices
                     continue
+                elif not dev_params.startswith('/dev/'):
+                    # will compare params directly
+                    pass
                 else:
                     (tmp_major, tmp_minor) = block_name_to_majorminor(dev_params.lstrip('/dev/'))
 
-            if (tmp_major, tmp_minor) == device_majorminor:
+            if (device_majorminor and (tmp_major, tmp_minor) == device_majorminor) or \
+               (device_majorminor is None and dev_params == device):
                 vm_name = xl_ctx.domid_to_name(int(vm_xid))
                 frontend = block_devid_to_name(int(devid))
                 return {"xid":int(vm_xid), "frontend": frontend, "devid": int(devid), "vm": vm_name}
@@ -290,7 +302,12 @@ def block_attach(vm, backend_vm, device, frontend=None, mode="w", auto_detach=Fa
         else:
             raise QubesException("Device %s from %s already connected to VM %s as %s" % (device, backend_vm.name, attached_vm['vm'], attached_vm['frontend']))
 
-    xl_cmd = [ '/usr/sbin/xl', 'block-attach', vm.name, 'phy:/dev/' + device, frontend, mode, str(backend_vm.xid) ]
+    if device.startswith('/'):
+        backend_dev = 'script:file:' + device
+    else:
+        backend_dev = 'phy:/dev/' + device
+
+    xl_cmd = [ '/usr/sbin/xl', 'block-attach', vm.name, backend_dev, frontend, mode, str(backend_vm.xid) ]
     subprocess.check_call(xl_cmd)
 
 def block_detach(vm, frontend = "xvdi", vm_xid = None):

dom0/qvm-tools/qvm-block

@@ -37,6 +37,8 @@ def main():
 
     parser = OptionParser (usage)
     parser.add_option ("-l", "--list", action="store_true", dest="do_list", default=False)
+    parser.add_option ("-A", "--attach-file", action="store", dest="file_path", default=None,
+                        help="Attach specified file instead of physical device (syntax: qvm-block -A file backend-VM frontend-VM)")
     parser.add_option ("-a", "--attach", action="store_true", dest="do_attach", default=False)
     parser.add_option ("-d", "--detach", action="store_true", dest="do_detach", default=False)
     parser.add_option ("-f", "--frontend", dest="frontend", 
@@ -48,8 +50,11 @@ def main():
 
     (options, args) = parser.parse_args ()
 
+    if options.file_path:
+        options.do_attach = True
+
     if options.do_list + options.do_attach + options.do_detach > 1:
-        print >> sys.stderr, "Only one of -l -a -d is allowed!"
+        print >> sys.stderr, "Only one of -l -a/-A -d is allowed!"
         exit (1)
 
     if options.do_attach or options.do_detach:
@@ -64,10 +69,16 @@ def main():
         vm = qvm_collection.get_vm_by_name(args[1])
         if vm is None:
             parser.error ("Invalid VM name: %s" % args[1])
-        dev_list = block_list()
+        if options.file_path:
-        if not args[0] in dev_list.keys():
+            dev = {}
-            parser.error ("Invalid device name: %s" % args[0])
+            dev['vm'] = args[0]
-        dev = dev_list[args[0]]
+            dev['device'] = options.file_path
+            dev['mode'] = 'w'
+        else:
+            dev_list = block_list()
+            if not args[0] in dev_list.keys():
+                parser.error ("Invalid device name: %s" % args[0])
+            dev = dev_list[args[0]]
         backend_vm = qvm_collection.get_vm_by_name(dev['vm'])
         assert backend_vm is not None
         kwargs = {}

misc/block_add_change

@@ -16,6 +16,11 @@ if [ -n "`ls -A /sys/$DEVPATH/holders 2> /dev/null`" ]; then
     xenstore-rm "$XS_KEY"
     exit 0
 fi
+# ... and "empty" loop devices
+if [ "$MAJOR" -eq 7 -a ! -d /sys/$DEVPATH/loop ]; then
+    xenstore-rm "$XS_KEY"
+    exit 0
+fi
 
 # Special case for CD
 if [ "$ID_TYPE" = "cd" ]; then
@@ -26,6 +31,11 @@ if [ "$ID_TYPE" = "cd" ]; then
     fi
     MODE=r
 fi
+
+# Special description for loop devices
+if [ -d /sys/$DEVPATH/loop ]; then
+    DESC=$(cat /sys/$DEVPATH/loop/backing_file)
+fi
 xenstore-write "$XS_KEY/desc" "$DESC" "$XS_KEY/size" "$SIZE" "$XS_KEY/mode" "$MODE"
 
 # Make sure that block backend is loaded

misc/qubes_block.rules

@@ -6,9 +6,6 @@ SUBSYSTEM!="block", GOTO="qubes_block_end"
 # Skip xen-blkfront devices
 ENV{MAJOR}=="202", GOTO="qubes_block_end"
 
-# Skip loop devices
-ENV{MAJOR}=="7", GOTO="qubes_block_end"
-
 # Skip device-mapper devices
 ENV{MAJOR}=="253", GOTO="qubes_block_end"