On Thu, May 22, 2003 at 10:22:12AM +1000, Ray Phillips wrote:

=> >All ccdconfig is basically doing is setting parameters in the driver
=> >for that CCD according to the settings in a configuration file
=> 
=> OK, so ccd drivers are loaded into memory at boot time and accept 
=> configuration values from ccdconfig which last until they're manually 
=> unconfigured or the machine's shutdown.

Well, you have to compile ccd as part of your kernel (it's not
available as an lkm).  Ccdconfig is the userland interface to the ccd
driver in the kernel.

=> That's very neat, but I 
=> suspect it's not an uncommon technique for unix systems?

Many drivers have some kind of userland configuration program
(ifconfig, vnconfig, cgdconfig, raidctl etc.).  Some (like the
RAIDframe "raid" driver) require only an initial bootstrapping if they
are flagged to autoconfigure at boot.  When that is the case, they can
configure themselves during boot by inspecting the labels on disks and
using information from those partitions marked as RAID that are set to
autoconfigure.

=> So, provided /etc/ccd.conf is unchanged, even if "ccdconfig -u" is 
=> executed the ccd device will be reconfigured at the next reboot, even 
=> if the disks it was composed of have been removed.  I guess the only 
=> harm done in this case is to produce a few warning messages on the 
=> console?

Basically, yes.  If drives are missing or they move around (due to new
drives being added), then the ccdconfig will fail to configure on
boot.  Subsequent attempts to mount a CCD volume (e.g., when file
systems are being mounted from /etc/fstab) will fail with a "device
not configured" error.  But, the rest of the system will still work.

If you remove some or all of the disks of a CCD from your system, you
can move or delete /etc/ccd.conf to prevent the system trying to
configure the CCD on subsequent boots.

Cheers,

Paul.

e-mail: paul@gromit.dlib.vt.edu

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