diskimage-builder/elements/vm/block-device.d/10-partition
Ian Wienand 2c32c7ae1a Handle modern sfdisk and correctly align image partition
As described in the comments, sfdisk was rewritten for util-linux 2.26
(as shipped in F22) and now interprets arguments a sectors, rather
than cylinders.

The current partitioning line is "1 - - *" (start/size/type/bootable)
which means you start getting:

---
/usr/sbin/grub2-install: warning: this msdos-style partition label has
no post-MBR gap; embedding won't be possible.

/usr/sbin/grub2-install: warning: Embedding is not possible.  GRUB can
only be installed in this setup by using blocklists.  However,
blocklists are UNRELIABLE and their use is discoura ged..

/usr/sbin/grub2-install: error: will not proceed with blocklists.
---

when building images, because the start is interpreted by the new
sfdisk as sector 1 and it crams the partition right next to the MBR.

Specifying "-" for the size is undefined in the man page; even reading
the source it's not totally clear what "-" for the size does [2].  In
any case, the alignment is wrong in sectors or cylinders; we want to
be a multiple of 4KiB for best performance.

The intent here is to create one single, Linux, bootable, partition
taking up the whole disk starting at 1MiB, so "2048 + L *" makes this
clear.

We use the -uS argument to ensure both versions treat this start-value
as a sector offset (newer sfdisk essentially ignores the argument).
As described in the comments, bugs in the older sfdisk necessitate
usage of "--force".

Although we could choose more or less, it seems most common to align
to a 1MiB boundary (i.e. starting at sector 2048).  libguestfs has
some disucssion around --alignment and where it sets it's default to
this [3].  The 2.26-era sfdisk also defaults to putting partitions
here.  1MiB should be enough for GPT schemes in the future as well.

[1] https://github.com/karelzak/util-linux/blob/master/libfdisk/src/script.c#L1050
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1249893
[3] http://libguestfs.org/virt-resize.1.html

Change-Id: I2c2966f98d1d5ad4ebb433ea148b3b26c65dc1b5
2015-08-04 15:26:13 +10:00

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#!/bin/bash
if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
set -x
fi
set -eu
set -o pipefail
source $_LIB/die
[ -n "$IMAGE_BLOCK_DEVICE" ] || die "Image block device not set"
# Create 2 partitions for PPC, one for PReP boot and other for root
if [[ "$ARCH" =~ "ppc" ]] ; then
sudo sfdisk --force $IMAGE_BLOCK_DEVICE << EOF
0,8,41 *
,,L
;
EOF
else
# sfdisk changed around 2.26 and was largely rewritten. The old
# version defaults to c/h/s and interprets arguments as cylinders.
# The new version defaults to sectors.
#
# Luckily, the old version has a -uS flag (ignored by the new
# version) to interpret arguments as sectors. However, it
# incorrectly calculates the c/h/s offset when finding free space,
# and gets upset [1], requiring the use of --force.
#
# TODO: switch this to parted, or something saner (is there such a
# thing when talking about partitioning?)
#
# The below command creates a partition that starts at 1MiB --
# which is the standard place to start a partition these days --
# and fills up the disk. The zeros are to ignore the other 3
# primary partitions (probably not needed, but left for safety).
#
# [1] https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/1481158
sudo sfdisk -uS --force $IMAGE_BLOCK_DEVICE << EOF
2048 + L *
0 0;
0 0;
0 0;
EOF
fi
sudo partprobe $IMAGE_BLOCK_DEVICE
# To ensure no race conditions exist from calling partprobe
sudo udevadm settle
# If the partition isn't under /dev/loop*p1, create it with kpartx
DM=
if [ ! -e "${IMAGE_BLOCK_DEVICE}p1" ]; then
DM=${IMAGE_BLOCK_DEVICE/#\/dev/\/dev\/mapper}
# If running inside Docker, make our nodes manually, because udev will not be working.
if [ -f /.dockerenv ]; then
# kpartx cannot run in sync mode in docker.
sudo kpartx -av $TMP_IMAGE_PATH
sudo dmsetup --noudevsync mknodes
else
sudo kpartx -asv $TMP_IMAGE_PATH
fi
elif [[ "$ARCH" =~ "ppc" ]]; then
sudo kpartx -asv $TMP_IMAGE_PATH
fi
if [ -n "$DM" ]; then
echo "IMAGE_BLOCK_DEVICE=${DM}p1"
elif [[ "$ARCH" =~ "ppc" ]]; then
DM=${IMAGE_BLOCK_DEVICE/#\/dev/\/dev\/mapper}
echo "IMAGE_BLOCK_DEVICE=${DM}p2"
else
echo "IMAGE_BLOCK_DEVICE=${IMAGE_BLOCK_DEVICE}p1"
fi