[Vmdebootstrap-devel] Bug#767913: vmdebootstrap: Make room for grub on disk also when --bootsize is used

[Petter Reinholdtsen]

Package: vmdebootstrap
Version: 0.4-3
Severity: important
Tags: patch

At the moment it is impossible to combine the --grub and --bootsize
options in vmdebootstrap:

root at tjener:~# vmdebootstrap --distribution=jessie --image=test.img --verbose --grub --bootsize=256M
Creating disk image
Creating partitions
Creating filesystem ext4
Mounting /dev/mapper/loop0p2 on /tmp/user/0/tmpMlrrJq
Creating filesystem ext2
Mounting /dev/mapper/loop0p1 on /tmp/user/0/tmpMlrrJq/boot/
Debootstrapping
Give root an empty password
Removing udev persistent cd and net rules
Setting up networking
Updating the initramfs
Configuring grub2
Failed. Is grub2-common installed? Using extlinux.
Installing extlinux
Cleaning up
root at tjener:~# 

Dropping --bootsize work:

root at tjener:~# vmdebootstrap --distribution=jessie --image=test.img --verbose --grub 
Creating disk image
Creating partitions
Creating filesystem ext4
Mounting /dev/mapper/loop0p1 on /tmp/user/0/tmppsKvPT
Debootstrapping
Give root an empty password
Removing udev persistent cd and net rules
Setting up networking
Updating the initramfs
Configuring grub2
Installing extlinux
Cleaning up
root at tjener:~#

The reason is that --bootsize causes the /boot partition to start on
sector 0 on the disk, not leaving any space for grub to use.  I
discovered this while working on the btrfs patch, but submit this as a
separate bug report to make sure the fix is not lost even if no-one have
time to look at the btrfs issue.

This patch solve the issue by ensuring 1 MiB at the start of the disk is
reserved when --bootsize is used, to make sure it behave the same way
vmdebootstrap (and parted) is working when --bootsize isn't used.

--- vmdebootstrap.orig	2014-10-18 20:35:19.000000000 +0200
+++ vmdebootstrap	2014-11-03 05:34:47.319278095 +0100
@@ -243,13 +272,14 @@
         self.runcmd(['parted', '-s', self.settings['image'],
                      'mklabel', 'msdos'])
         if self.settings['bootsize'] and self.settings['bootsize'] is not '0%':
-            bootsize = str(self.settings['bootsize'] / (1024 * 1024))
+            reserved = 1 # MiB space for boot loader / grub
+            bootend = str(reserved + (self.settings['bootsize'] / (1024 * 1024)))
             self.runcmd(['parted', '-s', self.settings['image'],
-                         'mkpart', 'primary', 'fat16', '0', bootsize])
+                         'mkpart', 'primary', 'fat16', str(reserved), bootend])
         else:
-            bootsize = '0%'
+            bootend = '0%'
         self.runcmd(['parted', '-s', self.settings['image'],
-                     'mkpart', 'primary', bootsize, '100%'])
+                     'mkpart', 'primary', bootend, '100%'])
         self.runcmd(['parted', '-s', self.settings['image'],
                      'set', '1', 'boot', 'on'])
 
-- 
Happy hacking
Petter Reinholdtsen