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From: Robert Raschke <rrplan9@tom...>
Subject: venti backup example vs. 2GB
Date: Mon, 25 Sep 2006 22:11:31 +0100

Hi,

I've been using a backup script modelled on the example in
/sys/src/cmd/venti/backup.example and the other day it "just" stopped
working.  On debugging I found that I have now reached the beginning
of the fifth 500MB arena.  The script uses awk to calculate the
starting byte offset and that fails with a floating point error (!)
when we go beyond the 2G mark.

I resorted to a fairly brutal use of bc(1) and that seems to work.
Here's what I use now (I flipped the 2nd and 3rd parameter to the x fn
to make printing from bc easier):

#!/bin/rc

rfork e
. bkup.info
fn x {
	echo x $*
	y=$1
	if(~ $#$y 0){
		$y=0
	}
	echo venti/wrarena -h venti_backup_server -o $3 $2 $$y
	end=`{venti/wrarena -h venti_backup_server -o $3 $2 $$y | grep '^end offset ' | sed 's/^end offset //'}
	if(~ $#end 1 && ! ~ $$y $end){
		$y=$end
		echo '#' `{date} >>bkup.info
		whatis $y >>bkup.info
	}
}
hget http://127.1:8000/index | 
awk '
/^index=/ { blockSize=0+substr($3, 11); }
/^arena=/ { arena=substr($1, 7); }
/^	arena=/ {
		start=substr($5, 2, index($5, ",")-2);
		printf("\"x \"; \"%s \"; \"%s \"; s=%s-%s; print s;", arena, $3, start, blockSize);
	}
' |bc -s |rc


Robby