joel linux # make O=/root/xen-build/dom0-2.6.16.49/ -j3
  GEN    /root/xen-build/dom0-2.6.16.49/Makefile
  CHK     include/linux/version.h
  SYMLINK include/asm -> include/asm-i386
  UPD     include/linux/version.h
  Using /usr/src/linux-2.6.16.49-xen as source for kernel
  /usr/src/linux-2.6.16.49-xen is not clean, please run 'make mrproper'
  in the '/usr/src/linux-2.6.16.49-xen' directory.
make[1]: *** [prepare3] Error 1
make: *** [_all] Error 2
make: INTERNAL: Exiting with 4 jobserver tokens available; should be 3!