xen: stop using loop device in run.py

This patch eliminates use of losetup in run.py when running OSv
on Xen. Instead of creating a loop device pointing to qcow2 or
raw image, run.py adds an entry to the xl config file pointing
directly to the OSv disk image like so:

disk=['/home/wkozaczuk/projects/osv/build/last/usr.img,qcow2,hda,rw']

or:

disk=['/home/wkozaczuk/projects/osv/build/last/usr.raw,raw,hda,rw']

In addition, we also enhance run.py to support 2nd disk when running
OSv on Xen. Finally, when executing run.py with '--dry-run', one can
see content of the xl config file which can be useful for
troubleshouting or manually running OSv using the xl utility.

Examples to run OSv on Xen:

./scripts/run.py -p xen #uses default qcow2 image build/last/usr.img

./scripts/run.py -nv -c 1 -p xen --script vif-bridge -b virbr0

./scripts/run.py -p xen --second-disk-image ./disk.raw

Fixes cloudius-systems#285
Fixes cloudius-systems#344

Signed-off-by: Waldemar Kozaczuk <jwkozaczuk@gmail.com>

scripts/run.py

@@ -370,6 +370,13 @@ def start_osv_xen(options):
             print("Unrecognized memory size", file=sys.stderr)
             return
 
+    disk_type = "qcow2" if options.image_file.endswith(".img") else "raw"
+    disk_value = "'%s,%s,hda,rw'" % (options.image_file, disk_type)
+
+    if cmdargs.second_disk_image:
+        second_disk_type = "qcow2" if options.second_disk_image.endswith(".img") else "raw"
+        disk_value = disk_value + ",'%s,%s,hda,rw'" % (options.second_disk_image, second_disk_type)
+
     if not options.novnc:
         vncoptions = re.match("^(?P<vncaddr>[^:]*):?(?P<vncdisplay>[0-9]*$)", options.vnc)
 
@@ -387,7 +394,7 @@ def start_osv_xen(options):
         "vcpus=%s" % (options.vcpus),
         "maxcpus=%s" % (options.vcpus),
         "name='osv-%d'" % (os.getpid()),
-        "disk=['/dev/loop%s,raw,hda,rw']" % os.getpid(),
+        "disk=[%s]" % (disk_value),
         "serial='pty'",
         "paused=0",
         "on_crash='preserve'"
@@ -411,23 +418,22 @@ def start_osv_xen(options):
         # Save the current settings of the stty
         stty_save()
 
-        #create a loop device backed by image file
-        subprocess.call(["losetup", "/dev/loop%s" % os.getpid(), options.image_file])
         # Launch qemu
         cmdline = ["xl", "create"]
         if not options.detach:
             cmdline += ["-c"]
         cmdline += [xenfile.name]
         if options.dry_run:
             print(format_args(cmdline))
+            print("\nContent of %s\n---------------------------" % xenfile.name)
+            for item in args:
+                print("%s" % item)
         else:
             subprocess.call(cmdline)
     except:
         pass
     finally:
         xenfile.close()
-        #delete loop device
-        subprocess.call(["losetup", "-d", "/dev/loop%s" % os.getpid()])
         cleanups()
 
 def start_osv_vmware(options):