Modified check_disklabel so that it's not dependent on dmesg output to determine

which linux partitions have been mapped to FreeBSD partitions.  Now the offset of
the 'a' partition is extracted from the disklabel and compared with the offset of
each partition found in /sys/block/$disk/$disk[1-9]* to find a match.

If the offset of the 'c' partition in the disklabel is 0, then we add the offset
of the FreeBSD slice to the offset of the 'a' partition before trying to find
a match.  This is to support FreeBSD's relative disklabel.

tmcd/linux/check_disklabel

 #! /bin/sh
 
+# Linux supports BSD disklabels, but it's not trivial to determine which device
+# name Linux assigned to the BSD partitions.  The way I understand it, the MBR
+# partitions (aka 'slices' in BSD parlance) get device names like hda[1-4].
+# Then any logical partitions contained in 'extended' partitions (types 0x5 and
+# 0x85) get handled, followed by the *BSD partitions.  The first 'logical'
+# partition found is given hda5, the second is hda6, and so on.
+
+# In order to figure this out, we need to first determine that the MBR
+# partition in question does in fact have a BSD disklabel, that Linux sees the
+# disklabel as valid, and that it has an 'a' partition.
+
 disk=$1
 part=$2
 
+disklabel_dump=/tmp/disklabel.$disk$part
+
 if [ $# -ne 2 ]; then
 	exit 1
 fi
@@ -20,13 +33,22 @@ if [ -z "$freebsd_slices" ]; then
 	exit 1
 fi
 
-dmesg_output=`dmesg | grep " *$disk$part: <bsd: $disk[0-9]* "`
-# Valid disklabels should be properly parsed by linux. If it didn't like
-# the label, we can't mount anything.
-if [ -z "$dmesg_output" ]; then
-	# invalid disklabel
-	exit 1
-fi
+## The only way to determine if a given slice has a BSD disklabel
+## is to look at the dmesg output.  The assumes that the relevant
+## info is still in the kernel's dmesg buffer.  It should be unless
+## we've been running for a long time.  This isn't likely to happen 
+## in a standard tftpboot/dongle boot setup though.
+#
+## XXX find another way to get this info in case the dmesg data
+## isn't available.
+#
+#dmesg_output=`dmesg | grep " *$disk$part: <bsd: $disk[0-9]* "`
+## Valid disklabels should be properly parsed by linux. If it didn't like
+## the label, we can't mount anything.
+#if [ -z "$dmesg_output" ]; then
+#	# invalid disklabel
+#	exit 1
+#fi
 
 (
 # Change partition types to empty for all other FreeBSD slices
@@ -46,15 +68,39 @@ done
 echo b		# Change to BSD disklabel mode
 echo p		# Print disklabel
 echo q		# Quit (don't write to disk)
-) | fdisk /dev/$disk 2> /dev/null | grep '^ *a:' > /dev/null
+) | fdisk -u /dev/$disk 2> /dev/null > $disklabel_dump
 rc=$?
 
+part_offset=`cat /sys/block/$disk/$disk$part/start`
+a_part_offset=`sed -n 's/^ *a: *\([0-9]*\) *.*$/\1/p' $disklabel_dump`
+c_part_offset=`sed -n 's/^ *c: *\([0-9]*\) *.*$/\1/p' $disklabel_dump`
+
+if [ x$a_part_offset = x ] || [ x$c_part_offset = x ]; then
+	#invalid disklabel
+	exit 1
+fi
+
+# Handle relative FreeBSD partitions
+if [ $c_part_offset -eq 0 ]; then
+	a_part_offset=$(( $a_part_offset + $part_offset ))
+fi
+
+a_part_linuxdev=''
+for partdev in /sys/block/$disk/$disk[1-9]*; do
+	[ $partdev = /sys/block/$disk/$disk$part ] && continue
+	start=`cat $partdev/start`
+	[ $start -eq $a_part_offset ] || continue
+
+	a_part_linuxdev=${partdev##*/}
+	break
+done
+
 # Valid disklabel, but no 'a' partition.
-if [ $rc -ne 0 ]; then
+if [ -z "$a_part_linuxdev" ]; then
 	exit 1
 fi
 
 # We have a valid disklabel with an 'a' partition.
 # Output the Linux device name for it.
-echo $dmesg_output | cut -d' ' -f3
+echo $a_part_linuxdev
 exit 0