Please note I don't know if it is the right way to proceed.
I had to do such modification in order to use sourcesdump as my
main dump archive.

Notes:
Wed May 24 10:54:51 EDT 2006 rsc
    If you want to pretend that sourcedump is your dump,
    then I think the best way to do that is to edit
    the "case dump" in /rc/bin/9fs to do 
    9fs sourcesdump; bind /n/sourcesdump /n/dump.
    
    Then history will work too.
    
    Russ


Reference: /n/sources/patch/sorry/yesterday-plan9-dump
Date: Mon May 22 17:36:21 CES 2006
Signed-off-by: xigh@free.fr
Reviewed-by: rsc

--- /rc/bin/yesterday	Mon May 22 17:27:11 2006
+++ /rc/bin/yesterday	Mon May 22 17:27:08 2006
@@ -151,7 +151,10 @@
 			'is not a backup day for' $xdump >[1=2]
 		exit 'bad date'
 	}
-	
-	$copy $xlast^$dumppath $xpath
+
+	if(test -e $xlast/plan9)
+		$copy $xlast^/plan9^$dumppath $xpath
+	if not
+		$copy $xlast^$dumppath $xpath
 }
 exit ''