[Merge] ~waveform/livecd-rootfs:general-tidy into livecd-rootfs:ubuntu/master

[Dave Jones]

I've added a commit with some comments detailing precisely what the awk code does. Here's some examples of the transformation, assuming "fstab.awk" contains the awk snippet proposed. First, demonstrating the basic transformation of the root mount's source, its options, its fsck order, and that no other lines are affected:

  $ cat fstab1
  /dev/mmcblk0p1  /boot/firmware  vfat    defaults        0       0
  # A random swap appears!
  /dev/mmcblk0p2  none            swap    sw              0       0
  /dev/mmcblk0p3  /               ext4    defaults        0       0

  $ awk -v root_fs_label=cloudimg-rootfs -v root_fs_options=discard,commit=30,errors=remount-ro -f fstab.awk < fstab1
  /dev/mmcblk0p1  /boot/firmware  vfat    defaults        0       0
  # A random swap appears!
  /dev/mmcblk0p2  none            swap    sw              0       0
  LABEL=cloudimg-rootfs   /       ext4    discard,commit=30,errors=remount-ro     0       1

Next demonstrating the addition of a root-mount in the event none is found, and removal of the UNCONFIGURED FSTAB warning:

  $ cat fstab2
  # UNCONFIGURED FSTAB

  $ awk -v root_fs_label=cloudimg-rootfs -v root_fs_options=discard,commit=30,errors=remount-ro -f fstab.awk < fstab2
  LABEL=cloudimg-rootfs   /       ext4    discard,commit=30,errors=remount-ro     0       1

Finally, demonstrating handling of multiple root-mount lines (elimination of all but the first with the source, option, and fsck transforms applied):

  $ cat fstab3
  /dev/sda1  /boot/efi  vfat    defaults        0       1
  /dev/sda2  /          ext4    defaults        0       0
  LABEL=writable  /     ext4    defaults        0       2

  $ awk -v root_fs_label=cloudimg-rootfs -v root_fs_options=discard,commit=30,errors=remount-ro -f fstab.awk < fstab3
  /dev/sda1  /boot/efi  vfat    defaults        0       1
  LABEL=cloudimg-rootfs   /       ext4    discard,commit=30,errors=remount-ro     0       1

If you wish, I can include these in the commentary in the shell script too, but it feels ... a bit bulky to me, and the awk isn't terribly complicated (vastly simpler than the line-noise of shell-interpolated-sed-interpreted regex it's intending to replace, at least to my eyes :)
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https://code.launchpad.net/~waveform/livecd-rootfs/+git/livecd-rootfs/+merge/450874
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