[Bug 245882] [NEW] Complex and stacked root file systems are not handled correctly

[gutschke]

Public bug reported:

Binary package hint: initramfs-tools

I noticed this bug with Ubuntu intrepid (8.10) and initramfs-tools
0.92ubuntu2, but I believe it actually exists in all older releases,
too. Possibly even upstream, but I did not check.

I have a server with several harddrives spread across multiple distinct
controller. These drives are joined in an md RAID6 array, and then
organized into logical lvm partitions.

"mkinitramfs" complete fails to understand this configuration and
"update-initramfs" subsequently fails to run. I managed to track down
the bug to "dep_add_modules()" in "/usr/share/initramfs-tools/hook-
functions".

This function attempts to find the root device in order to add the
appropriate kernel modules to the ram disk image. It correctly
determines that my root devices is "/dev/mapper/sys-sys", then looks up
the /sys entry "/dev/block/dm-0/slaves",  finds the underlying md
device, and ends up setting "$block" to "md0".

So far, so good. But it then erroneously assumes that all LVM devices
manage physical harddrives, and thus removes the trailing number from
the device name, assuming that it denotes a partition number. My device
name now becomes just "md" which is a non-existent device.

Not surprisingly, "mkinitramfs" then errors out when it tries to check
for the existence of "/sys/block/md".

The root cause of this error is the incorrect assumption that there is
only ever one level of indirection when stacking block devices. Instead,
after resolving the LVM device, it should proceed to check whether this
device is maybe part of another level of indirection. Typically, this
would be an md device (as it is in my case), but it could be a nested
LVM device.

I fixed this particular problem in my copy of the script (by commenting
out the line that removes the "partition" number) and discovered a
second related problem. When resolving md devices, "dep_add_modules()"
assumes that it only ever needs to look at the first member of the RAID
array. This assumption holds true only if all devices are connected to
identical controllers. But many motherboards these days have distinct
SATA chipsets for the different on-board ports. And a user might also
have added another PCI card to add additional ports.

So, instead of having a single "$block" variable, the code should create
a list of block devices when encountering md devices, and consider all
of the list entries as possible candidates for kernel module
dependencies.

I was able to temporarily avoid this second issue by building all
necessary device drivers into my kernel image, but that is obviously
only a band-aid solution.

** Affects: initramfs-tools (Ubuntu)
     Importance: Undecided
         Status: New

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Complex and stacked root file systems are not handled correctly
https://bugs.launchpad.net/bugs/245882
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