RPi2 snapshot for armv7 won't boot.

[Mark Millard]

On 2017-Nov-1, at 4:17 PM, bob prohaska <fbsd at www.zefox.net> wrote:

> On Wed, Nov 01, 2017 at 03:51:17PM -0700, Carl Johnson wrote:
>> I had previously tried to upgrade my RPi2 12.0-CURRENT system from armv6
>> to armv7, but it then refused to boot.  
> 
> Was this done self-hosted, or using crochet? I've been trying for weeks
> (months?) to make the armv6-armv7 transition on a self-hosted system,
> without even getting it to finish buildworld, much less boot. If you
> are self-hosting please describe what you did to make it work as far 
> as it did.

[Sometime between -r324743 and -r325156 armv7
has been broken such that /sbin/init fails,
apparently no matter how the build is done.
I'm ignoring that issue here.]

One point against attempting a self-hosted builds
on a system initially installed with crochet-based
materials:

Crochet has one major configuration problem for
reliability when swapping is to be involved on
the target: Crochet creates a context using a
swapfile instead of using a swap partition.

See bugzilla 206048 about the swapfile issue.

An RPI2 self-hosted likely(?) swaps extensively at
times. ("Only" 1 GiByte of RAM but clang is built,
for example.) I expect that having swap space is a
requirement to have self-hosting work. I'm not
familiar with what a near-minimal size might be.

I'm not claiming this explains what you might be
seeing. But the use of swapfiles is a known
problem, apparently known long before that bugzilla
submittal was made (2016-Jan-08).

My experience has lead me to always use swap
partitions --and never swap files.


Another issue is significant swapping activity is
likely not a good match to most sdcards. For this
class of devices, I normally configure causing the
root file system and swap space to be on a USB
drive, such as a USB SSD. So mostly it is the
kernel and earlier stages that come from the
sdcard and the sdcard is otherwise little used
in normal operation.

I have not tried a self-hosted build in some time
and other things are blocking such activities for
now.

===
Mark Millard
markm at dsl-only.net