resize script should be disabled after first boot, should not resize if user touched the partitioning

[stapelberg]

As reported by mrvnr on #debian-arm.

[stapelberg]

Patch by mrvnr:

--- rpi3-resizerootfs.orig      2017-10-25 12:25:11.508018334 -0400
+++ rpi3-resizerootfs   2017-10-26 20:04:05.881209721 -0400
@@ -58,6 +58,33 @@
 sub partition_table_entry { 16; }
 sub partition_table_start_offset { 8; }
 sub partition_table_length_offset { 12; }
+sub partition_count { 4; }
+sub partition_signature_len { 2; }
+sub tablelength { partition_table_entry() * partition_count() + partition_signature_len(); }
+
+# The contents of $original_partition_table must be updated whenever the
+# partition layout on the SD card image changes.
+# This layout matches
+# https://people.debian.org/~stapelberg/raspberrypi3/2017-10-08/2017-10-08-raspberry-pi-3-buster-PREVIEW.img.bz2
+my $original_partition_table = pack('H4' x (tablelength()/2),
+    "0020", "2100", "0c3e", "1826", "0008", "0000", "0058", "0900",
+    "003e", "1926", "837a", "3b7f", "0060", "0900", "00e0", "1500",
+    "0000", "0000", "0000", "0000", "0000", "0000", "0000", "0000",
+    "0000", "0000", "0000", "0000", "0000", "0000", "0000", "0000",
+    "55aa");
+
+sub check_orig_partition_table {
+    my ($offset, $len, $bytes) = @_;
+    sysseek($root, $offset, SEEK_SET)
+        or die qq|sysseek($offset): $!|;
+    my $buf;
+    sysread($root, $buf, $len)
+        or die qq|sysread(): $!|;
+    if ($buf ne $bytes) {
+        print "Partition table already modified\n";
+        exit 0;
+    }
+}

 sub read_uint32_le {
     my ($offset) = @_;
@@ -70,6 +97,9 @@
     return $val;
 }

+# Ensure partition table has not been modified by the user.
+check_orig_partition_table(boot_code(), tablelength(), $original_partition_table);
+
 my $entry_offset = boot_code() + (partition_table_entry() * ($pno - 1));
 my $start     = 512 * read_uint32_le($entry_offset + partition_table_start_offset());
 my $oldlength = 512 * read_uint32_le($entry_offset + partition_table_length_offset());

Patch for rpi3-resizerootfs.service:

--- rpi3-resizerootfs.service.orig      2017-10-26 14:41:07.034008352 -0400
+++ rpi3-resizerootfs.service   2017-10-26 20:15:43.062609923 -0400
@@ -6,6 +6,7 @@
 [Service]
 Type=oneshot
 ExecStart=/usr/bin/rpi3-resizerootfs
+ExecStart=/bin/systemctl --no-reload disable %n

 [Install]
 RequiredBy=systemd-remount-fs.service

[stapelberg]

We should also move the script to usr/sbin.