linux-kernel - Auto loading of kernel modules COLD/HOT BOOT

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Date:	Fri, 18 Sep 2009 02:36:37 -0700 (PDT)
From:	vprabu vprabu <prabu_online2005@...oo.com>
To:	linux-hotplug@...r.kernel.org
Cc:	linux-pci@...r.kernel.org, linux-usb@...r.kernel.org,
	kernelnewbies@...linux.org, linux-kernel@...r.kernel.org
Subject: Auto loading of kernel modules COLD/HOT BOOT

Hi All,

This is prabu .

I am new to kernel hacking ; i had been an application guy; now focusing into the fundamentals of linux kernel. I really have little knowledge about the kernel, modules and auto loading of modules.After a lot of googling ,i am now much perplexed :-)  Most of the articles are contradictory to each other and not very clear ( or not so simple at my level to comprehend)

1. How does a linux distribution know which feature is to be set in kernel and which one as a module.

2. Now after installation, i reboot the server ....( COLDPLUG )

*. Does the hardware probing is done first and then the relevant drivers are loaded for the hardware found. If so how is this achieved.

( or )

*. Else if the hardware driver is loaded FIRST from modprobe.conf and does it go in search of a corresponding device supported by the driver?

ie. Need to know a device is found first and its corresponding driver is loaded or the driver is loaded first which brings up the device

3. HOTPLUG ......

*. I now add a new network card to the PCI slot. ( 2.6 )

*. I assume that the PCI controller sends a signal to the kernel that a new device is added

*. The new device's firmware details like vendor id, prod id is propogated to /sys file system.

*. udevd tries to load the device drivers containing that particular vendor id in /lib/modules/kernel.xx/net

i have a doubt ... like.. does it search only /etc/modprobe.conf or all the modules under /lib/modules.

4. How does the same hotplug and cold plug happen in case of 2.4 kernels.

where does kmod , kerneld come into picture

5.  What is the main role of rc.sysinit -- does this handle device and drivers.

6. Dont know when to put an entry in modprobe.conf and when not to.

7. why does lsmod show something different from modprobe -c

8. How does modprobe -c get those values. why does it vary with lsmod output

9. There are two SCSI hostadapters of same type. Do i need  to load the module twice for it or once?

In simple words how a device driver is loaded at boot/hotplug for 2.4 and 2.6 kernels

I know each one is inter-related but dont know how they are?. I cant find any good article to explain the 

working of modules in simple words (both 2.4 / 2.6 with examples)

Any help in this regard is much appreciated....

Prabu

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