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Date: Sat, 1 Aug 2009 10:01:56 +0200
From: =?utf-8?B?SsOhbiBPTkRSRUogKFNBTCk=?= <ondrejj@salstar.sk>
To: Alexander Graf <agraf@suse.de>
Cc: Glauber Costa <glommer@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"avi@redhat.com" <avi@redhat.com>
Subject: Re: [PATCH] unbreak booting with virtio
Message-ID: <20090801080156.GE2701@salstar.sk>
References: <1249064349-799-1-git-send-email-glommer@redhat.com>
	<C78D67C7-C0CF-48BE-AB0E-85C1F02171A0@suse.de>
	<20090801070455.GD2701@salstar.sk>
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On Sat, Aug 01, 2009 at 09:04:55AM +0200, Ján ONDREJ (SAL) wrote:
> On Fri, Jul 31, 2009 at 09:55:39PM +0200, Alexander Graf wrote:
> >
> > On 31.07.2009, at 20:19, Glauber Costa <glommer@redhat.com> wrote:
> >
> >> cp "$1" "$2"
> >> +sum=$(echo "obase=8; $sum" | bc)
> >> printf "\\$sum" | dd of="$2" bs=1 count=1 seek=$size conv=notrunc 2>/ 
> >> dev/null
> 
> May be it's better to use awk:
> 
> echo $sum | awk '{ printf("%c", $1) }' \
>   | dd of="$2" bs=1 count=1 seek=$size conv=notrunc 2>/dev/null
> 
> This version accepts decimal $sum, does not need conversion to octal.

Ane may be it's better to write whole checksum in awk, it's faster and
cleaner. See attached patch (I am sorry, I don't know how to use git-email).

		SAL

diff --git a/pc-bios/optionrom/signrom.sh b/pc-bios/optionrom/signrom.sh
index 4273d1f..065b6a9 100755
--- a/pc-bios/optionrom/signrom.sh
+++ b/pc-bios/optionrom/signrom.sh
@@ -18,28 +18,31 @@
 #
 # Copyright Novell Inc, 2009
 #   Authors: Alexander Graf <agraf@suse.de>
+#            Jan Ondrej (SAL) <ondrejj(at)salstar.sk>
 #
 # Syntax: signrom.sh <input> <output>
 
 # did we get proper arguments?
 test "$1" -a "$2" || exit 1
 
-sum=0
-
-# find out the file size
-x=`dd if="$1" bs=1 count=1 skip=2 2>/dev/null | od -t u1 -A n`
-#size=`expr $x \* 512 - 1`
-size=$(( $x * 512 - 1 ))
-
-# now get the checksum
-for i in `od -A n -t u1 -v "$1"`; do
-    # add each byte's value to sum
-    sum=$(( $sum + $i ))
-done
-
-sum=$(( $sum % 256 ))
-sum=$(( 256 - $sum ))
-
-# and write the output file
-cp "$1" "$2"
-printf "\\$sum" | dd of="$2" bs=1 count=1 seek=$size conv=notrunc 2>/dev/null
+od -A n -t u1 -v "$1" | awk '
+    BEGIN {
+        checksum=0
+        # last byte will be replaced by checksum
+        last=-1
+    }
+    {
+        # go over all record in row
+        for(i=1; i<=NF; i++) {
+            checksum+=$i
+            if (last>=0) {
+                printf "%c", last
+            }
+            last=$i
+        }
+    }
+    END {
+        # compute checksum
+        printf "%c", 256-(checksum%256)
+    }
+' > $2