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Re: ide-scsi puzzle (for me, anyway)

Paul E Condon <pecondon@quiknet.com> wrote:

I recently migrated from 2.2.x to 2.4.18 kernel. I'm running Woody. I have
a CD reader and a separate CD reader/burner. The both were working before
the migration. After the migration the CD reader would not mount known good
CDs. I fixed this by changing the line in fstab for /cdrom to specify a SCSI
device. In the process of investigating, I tried to set up CD reading on the burner. To to this I had to specify /dev/scr1. So I got everything working,... But lilo.conf contained

and no mention of hdc. So, on a lark, I commented out the above append and
reran lilo and rebooted. Both CD drives continued to work, and both drives
appear as SCSI devices when I run

cdrecord --scanbus

Cdrecord 1.10 (i686-pc-linux-gnu) Copyright (C) 1995-2001 J?rg Schilling
Linux sg driver version: 3.1.22
Using libscg version 'schily-0.5'
cdrecord: Warning: controller returns wrong size for CD capabilities page.
	0,0,0	  0) '        ' '50X CD-ROM      ' '2.2B' Removable CD-ROM
	0,1,0	  1) 'HP      ' 'CD-Writer+ 9300 ' '1.0b' Removable CD-ROM
	0,2,0	  2) *
	0,3,0	  3) *
	0,4,0	  4) *
	0,5,0	  5) *
	0,6,0	  6) *
	0,7,0	  7) *

Where does the 2.4.18 kernel get the info to map these ide devices to scsi?
Is this story believeable to the experts? Or what might I be doing wrong in
investigating this? Since, both drives seem to work, is it safe to just leave
this problem expecting that they will continue to work through future upgrades
of the software? I think the change in CD drive support happened when I
moved to kernel 2.4.18, because I can't think of anything else I have done,
but maybe there is an entirely different cause. Any ideas?

I had the same experience as you just described. I have not got it all figured out yet, but it has something to do with the use of "initrd.img" in the 2.4.X Debian kernels (I "think"). When you use the initrd process, ALL the things that were compiled as modules are loaded and available during boot-up. This keeps the kernel size to a resonable value that can fit on a floppy for emergency / recovery use, BUT also allows full system capabilities when needed during "normal" boot up. This is the meaning of a "modular kernel", which the 2.4.X series are supposed to be. The bottom line is that if you are using one of the "stock" pre-compiled kernel images from Debian, then ALL the neede modules (ide-scsi, sr_mod, sg, etc) for SCSI emulation of IDE CDROMS are available during boot or loaded as needed during normal ops. You can do some neat things by using an "alias" line in your /etc/modules.conf file to get the proper modules loaded whenever a certain device is accessed, i.e. "alias cdrom1 sr.o" I suspect that when you run the scanbus command it figures out the necessary modules and loads them automagically for you. You can probly get a bit of insight by running a "lsmod" command before and after running scanbus and note the changes...dunno.

I found the "CD-Writing HOWTO" at: http://www.tldp.org/HOWTO/CD-Writing-HOWTO.html contained a LOT of useful information and it gave me a bit of insight into the overall process. Reading the man pages on initrd also give some information, although it is a bit cryptic.

And is the warning about the wrong size for CD capabilities page important? How
can this be fixed? I don't think I had this message the last time I was working
with the burner.

I have not seen this warning...dunno.

I would like to see a "HOWTO"-like explaination of the use of INITRD. I think this is the key to undestanding what is going on, but he current docs leave me confused. I am missing something & cannot connect all the dots...

-Don Spoon-

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