[coLinux-users] Re: Block device aliasing for dual-boot

[Ian A. <ia...@ab...>]

On 07/10/2004 19:06, Shi, Jue wrote:
> I just upgraded to snapshot (20041006) and found a commend in the default
> XML file the new block device alsasing stuff.
> Is there more detail info about it, especially how to use it for dual-boot
> system and how it works?
> 
> I have setup the colinux successfully to boot into my suse partion and got
> it running. The problem is that the fstab and the network need to be changed
> to get it work. Then these setting need to be changed back in order to boot
> into suse (not through colinux). 
> 
> My question is: can the block device aliasing help in this situation?

I tried block device aliasing for dual-booting Gentoo.  Like 
yourself, I wanted to avoid having two different versions of 
/etc/fstab.  However, in its current form, block device aliasing is 
pretty useless for this task.  For example, if you specify "hda1" as 
an alias name, the current version of the aliasing code creates a 
device called "hda/1" so it ends up with /dev/hda/1 instead of 
/dev/hda1.  Of course, this is incompatible with the normal device 
names when I boot Gentoo natively.

I hope the aliasing code will change to use the standard device 
names.  In the meantime, I use some devfsd rules to create and 
destroy symlinks from the cobd/X device names to the hdaX device names:

REGISTER ^cobd/([0-9]+)$ CFUNCTION GLOBAL mksymlink $devname hda\1
UNREGISTER ^cobd/([0-9]+)$ CFUNCTION GLOBAL unlink hda\1

The "\1" at the end of the rules gets substituted with the cobd 
device number, so in my colinux.xml file I make sure the 
block_device index values match the hda partition numbers. 
(Actually, I use hdc instead of hda on my system.)  An alternative 
would be to have separate rules for each partition.  Something like 
that would be necessary when the cobd devices are spread over more 
than one disk.

On Gentoo, I put those rules into a file called "mycolinux" in the 
/dev/devfs.d directory.  The /dev/devfsd.conf file contains ends 
with an INCLUDE rule that picks up these custom rules:

# Support additional config installed by packages ...
INCLUDE /etc/devfs.d

Then I just have to make sure I set the "root=" kernel option in my 
colinux.xml file to correspond with my root partition.  For example, 
if my root partition was /dev/hda2, I would set root=/dev/cobd/2.

I have various Windows partitions in my /etc/fstab which have no 
corresponding cobd devices defined (for obvious reasons!).  These 
are normally mounted at boot time when I boot Gentoo natively and of 
course fail to mount when I boot through coLinux.  This does not 
stop my Gentoo system booting up though.

I haven't set up networking yet.

> Another question is regarding the initrd file. Is it possible to use it to
> solve my problem above?

I don't think so, but I'm not sure what's in the initrd.  I'll 
probably find out when I try and set up networking!