Re: [PATCH] unbreak booting with virtio

Ján ONDREJ (SAL)
2009-08-01T08:01:56Z

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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

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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

# 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)
+ }