[Buildroot] [PATCH 1/2] first_boot_rootfs_resizer: New Package.

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Hello,

On Fri, 23 Dec 2016 14:41:59 +0100, daggs wrote:

> > We clearly shouldn't have an "unclear" license for such a package.  
> the file is ported from the odroidc2 buildroot, I've marked it unclear because it doesn't states it's license anywhere.

Would be good to get a clarified license, especially when the source
code is inside Buildroot itself.
> > > +ROOT=$(cat /proc/cmdline | tr ' ' '\n' | grep root= | cut -f 2 -d =)  
> > 
> > This will fail badly if you have a GPT partition table and root= is
> > using the partition UUID, like:
> > 
> > 	root=UUID=xyz
> >   
> I see, that should be the proper way to detect the rootfs file system?

One way would be to use the Busybox "rdev" applet, but it's not enabled
in our default configuration. You could run "stat /" where the "Device"
fields tells you the block device that was mounted as the root
filesystem. But not that trivial to go from this (major/minor) to the
actual /dev/.

I'm not sure there's a good and simple way to achieve that I'm afraid.

> > > +DEV=$(echo ${ROOT} | sed 's/p[0-9]\+$//g')  
> > 
> > This only works for mmcblkXpY case, but not for sdXY  
> correct, will see how I can generalize it more.

It's actually not that easy to generalize, except of course if you
restrict yourself to sdXY and mmcblkXpY.

> > > +if [ -f /.first_boot ]; then
> > > +	echo "Resizing fs, please wait... upon finish the system will be restarted"
> > > +	# ok, its the very first boot, we need to resize the disk.
> > > +	p2_start=`fdisk -l ${DEV} | grep ${PART} | awk '{print $2}'`
> > > +	p2_finish=`fdisk -l ${DEV} | grep sectors | awk '{printf $5}'`  
> > 
> > This will not work with the Busybox fdisk, which is the default in
> > Buildroot:
> > 
> > Disk /dev/sda: 256.0 GB, 256060514304 bytes
> > 255 heads, 63 sectors/track, 31130 cylinders
> > Units = cylinders of 16065 * 512 = 8225280 bytes
> > 
> >    Device Boot      Start         End      Blocks  Id System
> > /dev/sda1   *           1        3648    29295616  83 Linux
> > /dev/sda2            3648        4644     8000512  82 Linux swap
> > /dev/sda3            4644       31131   212761600  83 Linux  
> I'm pretty sure I've tested it with busybox's fdisk.

Well, to find the size of the block device, you grep for "sectors". The
only line matching with Busybox fdisk is:

255 heads, 63 sectors/track, 31130 cylinders

Which doesn't contain the size (at least not the size in sectors)

> > Using sfdisk is probably more appropriate here, as it's meant to be
> > used for scripting.  
> ok, will check.

But sfdisk is not in Busybox, so make sure to select the right package.

> > Also, this logic doesn't work if the root filesystem is mounted
> > read-only, since you expect to be able to remove .first_boot, and
> > remove the script itself.  
> so essentally, if the fs is read only, there is no way to remove it.
> so the right way is to check every boot if the fs is maxed out to the boot dev and resize it if not.
> am I correct?

Well, what if you're read-only but the root filesystem doesn't take the
whole space? Perhaps you can check in 'mount | grep " / "' whether it's
mounted read-only or not?

> > Why wouldn't the S00resizefs script directly do the resizing work?  
> as said above, I've ported it from the odroidc2 buildroot, so I didn't tried to change it too much.

Since the source code is part of Buildroot and we don't intend to
resync with the odroidc2 stuff, please make it more Buildroot-ish.

Thanks a lot!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com