Bug#370556: initramfs-tools: does not handle cryptroot-on-lvm properly

[Daniel Kahn Gillmor <dkg-debian.org@fifthhorseman.net>]

(hi again, David!)

On June 6, maks@sternwelten.at said:

 > On Mon, Jun 05, 2006 at 05:05:15PM -0400, Daniel Kahn Gillmor wrote:
 >
 > > [0 root@squeak ~]# cat /proc/cmdline 
 > > root=/dev/mapper/croot ro
 > 
 > this is obviously wrong,
 > current cryptsetup scripts expect the cryptoroot to be set by cryptopts,
 > try
 > root=/dev/mapper/squeak0 cryptopts=cryptsource=/dev/mapper/croot
 > 
 > i never found the way those cryptopts are specified to be pretty,
 > README.initramfs is not yet enlighting on the subject,
 > adding Davic on cc.

Is my initial line really so wrong?  It seems to me that other systems
besides cryptsetup and lvm might care that the root= kernel param
should be correct.  That is, that it should match the block device
that will in fact be mounted as the root filesystem.  It seems a bit
odd to me to explicitly specify a device that i *don't* want to use as
my root filesystem in the root= kernel parameter...

Here's a cleaner proposal:

The scripts/local-top/lvm has an order of priorities:

0) If the vgup= parameter is passed to the kernel [0], bring up those
   comma-delimited volume groups (potentially more than one), in the
   order specified.  otherwise,

1) Try sourcing /conf/conf.d/lvm from within the initramfs and test
   for the presence of $VGUP.  If it is present, bring up the
   specified (comma-delimited?) volume groups.  otherwise,

2) Try to auto-detect the volume group to bring up based on the root=
   parameter, as currently auto-detected.

This scheme would let a sophisticated user bring up arbitrary volume
groups at boot time (pre-root filesystem) from the kernel args without
modifying the initrd.  

It would also give the lvm hook script a place to note down the proper
Volume Group.  A sufficiently sophisticated hook script could
automatically detect the proper underlying volume group needed and
write it to /conf/conf.d/lvm, in the same manner as the cryptroot hook
script writes /conf/conf.d/cryptroot.  This eliminates the need for
user-specified entries in the bootloader.

And in the simple, default case, this proposed lvm local-top script
would would behave as it currently does.  


The advantages of this proposal as i see them are:

a) The well-known semantics of the root= kernel parameter are not
   disturbed.

b) Given a smart enough hooks/lvm, a common user wouldn't need to
   write any configuration files or specify any parameters in the
   bootloader to have things Just Work with root-on-crypto-on-lvm.

If you think this is worth pursuing, i'm happy to take a crack at it
for your review.  And of course, if i'm terribly misguided, please tell
me!

Thanks for your work on this,

	--dkg   

[0] i just made up the name of kernel parameter "vgup=".  I would be
    happy for other, better suggestions.  Are kernel parameter names
    registered anywhere?