[rhelv6-list] module load order changed in initramfs

[Jon Masters]

On Wed, 2011-01-12 at 12:28 +0530, neo3 matrix wrote:

> Thanks for  reply.

No problem. Could I ask that you preserve standard mail formatting
convention by including a quoting character of some kind (in this case,
I've used one ">" to indicate your message, and ">>" to indicate your
quoting of my message, following standard convention. Gmail can do this
for you, and in fact will do so in the default configuration.

> > You don't :) Not directly. It requires the initramfs to actually be
> > run and for the module loading to take place in reaction to the
> > kernel detecting various devices.

> Ok... So I understood that unlike RHEL5, I cannot get drivers and
> their load order just by digging initramfs

RHEL5 generates a static initrd that contains a module load order. If
you add new hardware, and so forth, you need to rebuild the initrd
because it is static. It's simple, and convenient, but it's not as
flexible as RHEL6. RHEL6 uses a dynamic initramfs that contains many
possible modules that might be loaded, and scripts that load them. It
should be possible to use the same initramfs on other machines
(depending upon the configuration of the "dracut" tool, whether in host
only mode or not), and is much improved in many other ways.
 
> > Yea, there is a reasonable expectation that it will be identical 
> > across same boots of the same system, running the same kernel build.
>
> Yes, I am restoring the client image on same system, same hardware and
> using same kernel build.

In this case, why not use the initramfs that was supplied?

> So, I can easily get the drivers and their load orders as listed 
> above, which I used to save and pass it to the client while restoring 
> the client using min os.

Sounds like you're using a totally different "mini distribution" of your
own to do the restoration, and choosing the modules to load based upon
those loaded in RHEL. btw, this only works if you are using a similar
kernel, because if you're not, there's no guarantee that the modules
will be the same, work the same way, or have the same dependencies.

> This I cannot do with RHEL6 initramfs as their is no provision of
> getting drivers and their load order from initramfs on RHEl6.
> 
> So, how can I get such type of  drivers and their sequence specific to
> RHEL6?

There are two possibilities:

1). (what I would do) Have your "mini OS" ship with an array of drivers,
using a standard udev-based load environment, and let it load the
appropriate drivers automatically, like RHEL-6 does.

2). Extract the list of modules included in the initramfs for RHEL6 and
include all of those in your mini-OS. Load them as in "1", using udev.
You could write a minimal alternative wherein you include all of these
modules, then generate a modules.dep/modules.dep.bin and repeatedly call
"modprobe -b" with the module alias detected from running various tools
(again udev is the proper solution, but there are potential hacks).

Taking the list from the running RHEL-6 system, before problems arise,
as you say you are thinking about doing, will not be sufficient, unless
you do it on every boot of the system (and even then), because there is
no guarantee that additional drivers will not be loaded onto the system,
that the hardware won't be changed between boots, or that the kernel was
not upgraded to one that loaded a new or different module after reboot
(this would occur between minor releases of the RHEL-6 product).

I hope this helps. If you need further assistance, I suggest contacting
our GSS (support) and filing a ticket, or GES (consultancy group).

Jon.