On 19 Feb 09, Jonas Meurer wrote:
> Hey,
>
> Maks, I spent several hours now on debugging this issue, and all I found
> out is that the patch by Pyotr is correct if you don't want to change
> the way, how initramfs manages /dev/root.
>
Thanks for taking the time to examine my patch.
Basically, the problem is this: The major/minor of the root device can
change from one boot to another. This happens in the following cases:
1) when booting into the system after installing to or from removable
devices, i.e. USB sticks;
2) when adding/removing removable devices;
3) when adding/removing/recabling hard drives;
3) when adding/removing LVM volumes.
Therefore, relying on hardcoded root device names/numbers (i.e. 'dev/sda1' or
'Oxfe4') in the initrd leads to failure to mount the root device in
these cases.
The solution is to use persistent device names. If we're using LVM, we
use the names under '/dev/mapper' ('/dev/mapper/foo-bar' for unencrypted
LVM, or '/dev/mapper/foo-bar_crypt' for encrypted LVM). In all other
cases we can use the names provided for us by udev under
'/dev/disk/by-id'.
These names are passed to the initrd on the kernel command line and work
for any bootloader, whether Lilo, GRUB, or whatever.
'/dev/root' should point to the real root device.
In the case of encrypted and LVM root devices, third-party scripts are
responsible for creating and setting up the root device. Therefore, it
makes sense to have these scripts set up '/dev/root' also.
That's all there is to it. My patch solves the problem for the case of
dm-crypt+LVM. The case of unencrypted LVM will require another patch.
The remaining cases would require some patching of the top-level
initramfs code. parse_numeric() would then be unnecessary and could be
safely removed.
-PGB
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