[CUWiN-Dev] cuw_config_backend questions

[David Young]

On Thu, Sep 08, 2005 at 11:22:38AM -0500, Bill Comisky wrote:
> I can see that the root filesystem is mounted read/write in 
> initialize_config() in /usr/sbin/cuw_config_backend, where it calls 
> update_cuw_config_{hostname,nameservers}().
> 
> After seeing a smokeping plot of a node rebooting every 5-6 minutes all 
> weekend (only one node up, nothing tickling the watchdog) I started 
> wondering about flash erase-write cycles (which I admit I know next to 
> nothing), and whether the initialize_config() function counted for one at 
> every reboot.  I've seen estimates of 1e4 to 1e6 erase cycles for flash 
> memory.  At the low end that's a lifetime of about 35 days if you get an 
> erase cycle every 5 minutes, at the high end its closer to 10 years.
> 
> Looking again at initialize_config(), I'm not sure why we need need to 
> mount -u -w / at all.  The only files modified are in /etc or /var which 
> are both mfs filesystems.

I am looking at initialize_config() for the first time, myself.  I don't
understand why it remounts read-write, either.  Some of the subroutines
it calls will also remount read-write.

I would like to see the whole backend redone so that resynchronizing
the non-volatile configuration with the volatile configuration happens
in one place.  Something along these lines:

	config_files=/etc/cuw_config # et cetera

        touch /var/tmp/begin-reconfig
        # In POSIX, the timestamp resolution for files
        # is 1 second.  Wait one second before modifying
        # any files, so that find(1) or test(1) can tell
        # they have been modified since
        # /var/tmp/begin-reconfig was touched.
        sleep 1

        ###
        ### update configuration
        ###

        mount -u -w /
        cd /
        find $config_files -newer /var/tmp/begin-reconfig | \
            xargs pax -pe -rw /permanent/.
        # optionally remount read-only

I believe we will ultimately end up with fewer lines of code by
consolidating the "refresh non-volatile config" function in one place.

Dave

-- 
David Young             OJC Technologies
dyoung at ojctech.com      Urbana, IL * (217) 278-3933