Re: WARNING: expand-on-first boot might shrink your partition on Debian bookworm

["Bezdeka, Florian" <florian.bezdeka@siemens.com>]

On Thu, 2022-07-07 at 10:54 +0200, Henning Schild wrote:
> Am Thu, 7 Jul 2022 09:48:22 +0200
> schrieb Florian Bezdeka <florian.bezdeka@siemens.com>:
> 
> > Hi all,
> > 
> > here comes another Debian bookworm related problem. This time related
> > to expand-on-first-boot, which destroys my image during the fist boot.
> > 
> > The linux-util packages has been updated and includes some changes
> > related to partition alignment. See [1]. (Thanks Henning for pointing
> > me here.) It might happen now that the last partition is shrinked
> > instead of expanded.
> > 
> > This is especially relevant for setups where the last partition is the
> > root partition and where no more space is available (e.g. booting up a
> > wic image with qemu where disk size = image size)
> > 
> > The original partition table looked like this:
> > 
> > label: gpt
> > label-id: 8CC4BCD4-F7B9-45F1-A066-DFB4068D6DFC
> > device: /dev/sda
> > unit: sectors
> > first-lba: 34
> > last-lba: 4554194
> > sector-size: 512
> > 
> > After expand-on-first-boot it looks like that:
> > (note the last-lba field)
> > 
> > label: gpt
> > label-id: 5305C98F-17AD-4B41-9388-7DC319741C9D
> > device: talker-debian-bookworm-qemuamd64.wic
> > unit: sectors
> > first-lba: 34
> > last-lba: 4554320
> > sector-size: 512
> > 
> > Booting up again stops in the initrd with the following error:
> > 
> > (initramfs) [    1.978569] EXT4-fs (sda2): bad geometry: block count
> > 550586 exceeds size of device (550400 blocks)
> > 
> > resize2fs called from expand-last-partition.sh already throws a
> > warning resize2fs: New size smaller than minimum (550586)
> > 
> > Ideas welcome...
> > Taking over even more...
> 
> I think one idea as a quick hack in an affected layer could be to add
> more EXTRA_SPACE, but i did not try that. With more space a slight
> shrinking might just work. Or put a large fixes size in your wks ... or
> play with alignment there to avoid shrinking.

I played around with that as well, the problem is that you have to find
a matching value for EXTRA_SPACE to avoid the alignment. Once found it
may break again with one more package added to the image.

> 
> And the good solution would probably to detect that the disk is already
> "close to full" and simply step out early.
> 
> if /sys/class/block/sda/size - sum(/sys/class/block/sda/sda*/size) < 32M
> echo "Nothing to do"; exit 0

I like the idea but keep in mind that such sysfs or procfs entries
might not exist in all cases. There might be custom kernel
configurations out there with such features disabled. Might not be a
real world problem, but if so we would break such setups. So far we
only had dependencies to user space components.

> 
> Where 32M is made up, one should look up what the maximum shrink could
> be. I think we could even say 4M. Or we could use percentage ... if sum
> > = 0.95*size
> 
> Henning
> 
> > Best regards,
> > Florian
> > 
> > 
> > [1]
> > https://github.com/util-linux/util-linux/commit/921c7da55ec78350e4067b3fd6b7de6f299106ee
> > 
>