[U-Boot] [PATCH 3/4] sunxi: Add default partition scheme

[Maxime Ripard]

Hi,

On Thu, Nov 16, 2017 at 11:41:57AM +0000, Andre Przywara wrote:
> >> If I understand this correctly, these are default settings for
> >> U-Boot's "mtdparts default" command, which honestly I didn't even
> >> know existed so far.
> > 
> > No, this has nothing to do with MTD. It's a default GPT partitioning
> > scheme. And only when you want to create the table from U-Boot, it
> > will not mangle with any pre-existing partition table if there is any
> > (unless you tell U-Boot to overwrite it, of course).
> 
> This is what I tried to say: It only affects you if you use U-Boot's
> partitioning command, which you probably won't do if you are running an
> off-the-shelf distribution installer. Is that understanding correct?

It is :)

> >> So in a distribution scenario I wouldn't expect somebody to actually use
> >> this. Instead you boot from a (possibly unpartitioned) SD card with just
> >> U-Boot on it or from SPI flash, then launch an installer from somewhere
> >> (PXE, USB drive) and let it do its job. No U-Boot partition involved.
> >> And even if you use mtdpart, you can always override these default
> >> settings on the command line.
> > 
> > Like I was telling Alexander, that makes a number of assumptions, the
> > two most obvious one being that you have an installer and that you
> > want to use it, both with reasonable reasons on why they wouldn't be
> > true.
> > 
> > More tailored fit distros like ELBE, yocto or Buildroot will not have
> > an installer in the first place but an image.
> > 
> > And even if you have an installer for the distro you want to use, if
> > you ever go to production, you will not use it since the time spent to
> > flash a pre-filled image compared to running the installer is
> > significantly lower. And time is money :)
> > 
> > Just like plugging / unplugging microSD card isn't really realistic in
> > that scenario.
> 
> I don't argue this (see above) and surely understand that generic
> installers don't fly when it comes to bootstrapping devices.
> 
> But my understanding is that both Alex and Karsten don't really care
> about this usage scenario, but instead are more looking into generic
> distribution installers, which use U-Boot merely to launch grub.
> 
> Actually I wanted to help you out here by pointing out that their
> concerns don't really apply to this patch ;-)

It's good that we agree then :)

> >> Does mtdparts even use partition tables (MBR/GPT)? mtd sounds quite
> >> Android-y/embedded to me (passing partition information via command line).
> >>
> >> So apart from that I think it's good to have a default FAT/ESP
> >> partition, also for storing the environment.
> > 
> > What is the typical size of the files you usually put in there? My
> > actual question being is 128MB enough, way too big or too small? The
> > environment is just 128kB big at the moment, so it looks wayyyyy to
> > big for me, but I have no idea what is usually stored in an ESP
> > partition.
> 
> 128MB is actually quite fine. I tend to use 150MB or 100MB. The Ubuntu
> arm64 kernel is around 20MB, and you may want to store more than one of
> those on the ESP, along with an initrd. I understand that distributions
> may not use the ESP for that, but their own /boot partition. But this is
> their choice. Also other OSes (BSDs?) want to use the ESP, so being too
> miserly here may backfire.

Ok. Given Alexander and Emmanuel answers, I guess that would cover it
too, so we can leave it that way :)

> Do you feel that's too big? We are talking about at least 8GB eMMCs
> mostly here, right?

Yeah, well, I guess I don't like wasted space. If you give me the
choice between a partition mostly unused or the ability to store one
more ripped CD, I'll take the latter any day. But if you guys need
that space, I'm totally fine with it.

> >> In a MBR/GPT scenario I would expect a big partition covering the whole
> >> device causes headache later on.
> > 
> > What kind of headaches?
> 
> Just thinking if an installer wants to add partitions (swap, /home, ...)
> it might be easier if some space is actually left unpartitioned.
> But that's just my non-embedded experience, where adding partitions is
> easier and safer, compared to deleting or resizing an existing partition.

I guess I also have a side question here. How do the installers deal
with the ESP partition? Would they create a new filesystem on it no
matter what, or are they a bit smarter than that?

My actual question being what will happen if one stores the U-Boot
environment on that partition, and then runs an installer? Would the
environment be gone?

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 801 bytes
Desc: not available
URL: <http://lists.denx.de/pipermail/u-boot/attachments/20171117/5b5802fc/attachment.sig>