Where did you get them there devices ?

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Hi Mikkel;

This post is in order to start my own thread Re: Problem with random
disks mount sequence.



"Your explanation is of great
interest to me at the moment.  I am
trying
to trace exactly how the devices
attached to my computer first get
registered.  I just need someone to
point me to the mechanism or kernel
code.

On Wed, 2007-12-12 at 07:59 -0600,
Mikkel L. Ellertson wrote:
> Tim wrote:

> > 
> A slight correction. It is not the
BIOS oder that determines the of
> the drives under Linux. It is the
kernel. What I would expect to
> happen is that you would only have
the drivers for the drive with
> root file system loaded in the
initrd, 
This is handed over by grub from
BIOS to initrd?

> and the scan order would
What and where is the kernel
function that scans?  What does
scanning in
functional terms mean?  If you don't
have the name of the function off
the top of your head, suggest where
I might look in kernel code.

> always be the same unless you
physically change drive connections
or
> add drives. (Or use a kernel
parameter to change the order.)
> 
> With SATA drives and USB drives,
the USB drive should always be
> discovered later then the  SATA
drive because the usb_storage driver
> should not be loaded until after
the root file system is mounted.
>
But if the
> usb_storage module is in the
initrd, then things are not as
clear.
> It should still find things in the
same order, but in this case, it
> isn't.
> 
> One other thing that I should have
commented on earlier - there is
> nothing that says that the root
file system has to be on the first
> SCSI drive, so the system can use
that in determining what drive
> should be /dev/sda. It used to be
fairly common in dual boot systems
> to have Window on the first drive,
and Linux on the second drive.
> 

I know I can view attached devices
through cat /dev/* or cat /sys/*.
But those file systems just reflect
a read-only view of an existing
kernel file struct (I think).  How
does the kernel, as it scans, place
the data in the struct (or table)
and what are the structs called?
Isn't
hwconfig just a user view?  Again
pointing in the right direction is
sufficient for me?

> Mikkel
> -- 

I have been trying to trace (for
interest and completeness of
understanding) how device data first
gets into the kernel for over a
month now.  I have read endless
number of sites regarding standards,
naming protocols, address protocols,
modules, drivers, BIOS and grub.
All have been helpful and all have
been ultimately understandable.  But
words like "probes for", "registers"
etc. for devices are never
explained.

P.S.  I even have a manual (text
book) that purports to explain the
kernel code (2.6.7 or greater)
line-by-line, which mainly it does,
but
it seems to remain silent on
scanning and registering devices at
startup. Or, at least, I am
misreading because I can't find it."





-- 
Regards Bill


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