sipb-xen-losetup: a half-sane way to use losetup

You should use this instead of plain losetup; everything that uses this
will at least not have races with other things using this.

If it's missing a feature (e.g. a losetup argument) you want,
it shouldn't be hard to add.

svn path=/trunk/packages/sipb-xen-guest-installer/; revision=449

diff --git a/files/usr/sbin/sipb-xen-lvcopy b/files/usr/sbin/sipb-xen-lvcopy
index 5b83460..065cda2 100755 (executable)
--- a/files/usr/sbin/sipb-xen-lvcopy
+++ b/files/usr/sbin/sipb-xen-lvcopy
@@ -8,27 +8,8 @@ import time
 from subprocess import call, check_call, Popen, PIPE
 
 def losetup(source, offset=0):
-  # XXX we avoid colliding with other instances of ourself,
-  #     but when it comes to other loop-device users we just
-  #     pick a range things don't seem to use and hope...
-  lockfilename = '/tmp/losetup.lock'
-  os.close(os.open(lockfilename, os.O_CREAT+os.O_EXCL)) #lock
-  try:
-    loopdevice = None
-    for i in xrange(32,60): # totally arbitrary, just looks to be unused on black-mesa
-      filename = '/dev/loop%d'%i
-      if 0 == len(file(filename).read(1)):
-        loopdevice = filename # it's empty
-        break
-    if loopdevice is not None:
-      call(['losetup', '-o', str(offset), loopdevice, source])
-    else:
-      raise RuntimeError('out of loop devices for copying VM image: too many at once?')
-  finally:
-    os.unlink(lockfilename) #unlock
-  return loopdevice
-  # XX this means we can duplicate 28 at once.  Since it takes around 30s,
-  # this seems like an adequate capacity.
+  p = Popen(['sipb-xen-losetup', source, str(offset)], stdout=PIPE)
+  return p.communicate()[0].strip()
 
 def frob_copy_in_vm(target, *args):
   '''UNUSED: maybe we'll use this someday; it does isolate the frobber.'''