x86: preserve partition table on sysupgrade

With this patch sysupgrade will write directly to the partitions
instead of to the main disk.  The UUID is copied from the image
to the MBR as well.  This prevents the mbr from being completely
overwritten and losing the partition table.  The -p option has
been added to maintain the original behavior and overwite the
entire disk with the new image.  Tests have been added to ensure
that the image partitions match up with the active partitions.

Signed-off-by: Rob Mosher <nyt-openwrt@countercultured.net>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48682 3c298f89-4303-0410-b956-a3cf2f4a3e73

2 files changed, 51 insertions, 2 deletions

diff --git a/target/linux/x86/Makefile b/target/linux/x86/Makefile
index e4bc0d9a50..45bb8c7cac 100644
--- a/target/linux/x86/Makefile
+++ b/target/linux/x86/Makefile
@@ -13,6 +13,8 @@ FEATURES:=squashfs ext4 vdi vmdk pcmcia targz
 SUBTARGETS=generic xen_domu ep80579 geode kvm_guest 64
 MAINTAINER:=Felix Fietkau <nbd@openwrt.org>
 
+DEFAULT_PACKAGES += partx-utils
+
 KERNEL_PATCHVER:=4.4
 
 KERNELNAME:=bzImage
diff --git a/target/linux/x86/base-files/lib/upgrade/platform.sh b/target/linux/x86/base-files/lib/upgrade/platform.sh
index 73ab5ef079..86696aec04 100644
--- a/target/linux/x86/base-files/lib/upgrade/platform.sh
+++ b/target/linux/x86/base-files/lib/upgrade/platform.sh
@@ -55,12 +55,59 @@ platform_copy_config() {
 	fi
 }
 
+get_partitions() { # <device> <filename>
+	local disk="$1"
+	local filename="$2"
+
+	if [ -b "$disk" -o -f "$disk" ]; then
+		echo "Reading partition table from $filename..."
+		partx -r "$disk" -gbo NR,START,SECTORS > "/tmp/partx.$filename"
+	fi
+}
+
 platform_do_upgrade() {
 	platform_export_bootpart
+	disk="${BOOTPART%[0-9]}"
 
-	if [ -b "${BOOTPART%[0-9]}" ]; then
+	if [ -b "$disk" ]; then
 		sync
-		get_image "$@" | dd of="${BOOTPART%[0-9]}" bs=4096 conv=fsync
+		if [ "$SAVE_PARTITIONS" = "1" ]; then
+			get_partitions "$disk" bootdisk
+
+
+			#get block size
+			sectors="$(partx -r $disk -gbo SECTORS --nr 1:1)"
+			size="$(partx -r $disk -gbo SIZE --nr 1:1)"
+			ibs="$(($size / $sectors))"
+
+			#extract the boot sector from the image
+			get_image "$@" | dd of=/tmp/image.bs count=1 bs=512b
+
+			get_partitions /tmp/image.bs image
+
+			#compare tables
+			diff="$(grep -F -x -v -f /tmp/partx.bootdisk /tmp/partx.image)"
+			if [ -n "$diff" ]; then
+				echo "Partition layout is changed.  Full image will be written."
+				ask_bool 0 "Abort" && exit
+
+				get_image "$@" | dd of="$disk" bs=4096 conv=fsync
+				return 0
+			fi
+
+			#iterate over each partition from the image and write it to the boot disk
+			while read part start size; do
+			echo "Writing image to $disk$part..."
+				get_image "$@" | dd of="$disk$part" ibs="$ibs" obs=1M skip="$start" count="$size" conv=fsync
+			done < /tmp/partx.image
+
+			#copy partition uuid
+			echo "Writing new UUID to $disk$part..."
+			get_image "$@" | dd of="$disk" bs=1 skip=440 count=4 seek=440 conv=fsync
+		else
+			get_image "$@" | dd of="$disk" bs=4096 conv=fsync
+		fi
+
 		sleep 1
 	fi
 }