HOWTO: Putting cryptoloop back in Debian

Update 2010-11-20: It has been pointed out to me that dm-crypt can handle cryptoloop volumes. Thus, you may choose to ignore this HOWTO in favor of one on how to do that.

For reasons detailed in Debian Bug #559961 the cryptoloop module has been dropped from the Debian kernel as of the 2.6.32-trunk binary packages. I've filed a complaint at that bug. I know what I'm doing, and am unhappy that the Debian kernel maintainers have taken it upon themselves to gratuitously delete functionality from the Linux kernel image…

In the meantime, here's how you put cryptoloop back.

• Install the linux-source-2.6.xx package, where xx is your kernel version. You'll need to have the kernel headers somewhere where the makefile can find them; if you have troubles try installing linux-headers-2.6.xx as well.
• Make a /usr/src/cryptoloop directory.
• Put a copy of cryptoloop.c from /usr/src/linux-source-2.6.32/drivers/block/ (yes, it's still there) in your new cryptoloop directory.
• Go to the cryptoloop directory and create the following Makefile:
  

  obj-m := cryptoloop.o
      
  all:  
  	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules  
  
  clean:
  	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
  

  (Be careful that those tabs at the beginning of the make lines are hard.)

• Say "make all".
• As root, say:
  

  cp cryptoloop.ko /lib/modules/`uname -r`/kernel/drivers/block/
  depmod -a
  modprobe cryptoloop
  

If all goes well, you should be cryptolooping again. Remember that until Debian is (hopefully) fixed you will have to rebuild cryptoloop.ko whenever you upgrade your kernel. The cryptoloop.c source is unlikely to change, but you might want to check first.

Have fun. (B)