Re: Don't understand how devfsd and ide-scsi are working together

[Dave Carrigan <dave@rudedog.org>]

On Sun, 2003-04-13 at 03:31, Alan Chandler wrote:

> I have just upgraded to use devfsd and I seem to not have the scsi device 
> created by ide-scsi until I do something completely strange.  See below
> 
> /proc/scsi/scsi lists the device as scsi device 1 thus
> 
> kanger:/dev/scsi# more /proc/scsi/scsi
> Attached devices:
> Host: scsi0 Channel: 00 Id: 03 Lun: 00
>   Vendor: TEAC     Model: CD-R55S          Rev: 1.0J
>   Type:   CD-ROM                           ANSI SCSI revision: 02
> Host: scsi1 Channel: 00 Id: 00 Lun: 00
>   Vendor: PIONEER  Model: DVD-ROM DVD-104  Rev: 2.02
>   Type:   CD-ROM                           ANSI SCSI revision: 02
> Host: scsi2 Channel: 00 Id: 00 Lun: 00
>   Vendor: eUSB     Model: SmartMedia       Rev: 5.04
>   Type:   Direct-Access                    ANSI SCSI revision: 02
> 
> But if I do an ls of the supposidly correct directory
> 
> kanger:/# ls /dev/scsi/host1/bus0/target0/lun0/
> kanger:/# ls /dev/scsi/host1/bus0/target0/lun0/
> 
> I get nothing (ie the directory is empty)
> 
> As soon as I do the following (which theoretically has nothing to do with it)
> 
> kanger:/# ls /dev/scsi/host1/bus0/target0/lun2/
> ls: /dev/scsi/host1/bus0/target0/lun2/: No such file or directory
> 
> I can them immediately repeat the orginal
> 
> kanger:/# ls /dev/scsi/host1/bus0/target0/lun0/
> cd

I assume that the above two lines are a single command?


> and now get the "cd" device listed.
> 
> At the same time much of the rest of /dev comes to life /dev/cdroms appear for 
> instance (where it wasn't before) and it has two cd's mentioned.
> 
> Whats happening?

ide-scsi is just a emulation layer that presents the IDE bus as a SCSI
bus. To actually make use of SCSI devices on the IDE bus, you need to
load the appropriate module for the device type (in this case, sr_mod).
The /dev/scsi/.../lun*/ directories will be empty until you load those
modules.

However, because you specifically did a ls of /dev/scsi/.../cd, it
caused devfs to trigger a modprobe of sr_mod, and the device magically
appeared, along with the appropriate symlinks in /dev/cdroms.

You could have got the same behavior my manually modprobe'ing ide-scsi
and sr_mod.

-- 
Dave Carrigan
Seattle, WA, USA
dave@rudedog.org | http://www.rudedog.org/ | ICQ:161669680
UNIX-Apache-Perl-Linux-Firewalls-LDAP-C-C++-DNS-PalmOS-PostgreSQL-MySQL