RFC: Pre pull request for openbmc initfs updates

[Milton Miller II]

All, 

I have completed initial testing of my updates to initfs to allow 
running from RAM.  Comments on the option names and functions are 
welcome.  The branch is available at 

https://github.com/mdmillerii/openbmc/tree/wip-from-ram


There are a couple of use cases enabled by this series:

1) Allow the BMC to run without any access to the flash.

2) Allow running a new application layer while updating the flash.

3) Allow a new application layer to be tested without committing it 
   to flash.

4) Allow running the overlay totally from RAM with only white
   listed files saved at specific times.


This is implemented by having the following options in init:

- An option and hook to run a command that could download an image

- Alternatively use existing debug-init-sh hook

- An option to copy existing read-only file into RAM

- Mount an read-only file system image in RAM via a loop device

- An option to copy white listed files from read-write file system to 
  RAM for use at runtime  (can also use empty overlay but that would 
  loose   dropbear key, machine id, network settings)

- An option to suppress mounting Read-Write file system before creating 
  overlay


The following options control the behavior of /init in the initramfs:

- debug-init-sh : a previously existing hook to invoke a shell via 
  sulogin, can add or change options here

- openbmc-init-download-files  : will execute via sh -c the saved 
  contents of openbmcinitdownload u-boot variable (which can be 
  used to download files via http (wget) or tftp).

- clean-rwfs-filesystem : an existing option to remove , erase, and 
  restore files.  unless a image-rwfs exists via download this will 
  have the side effect of converting the read-write files ystem to 
  jffs2 our current build choice.

- copy-files-to-ram : copy files from the read-write files system to ram

- overlay-filesystem-in-ram : skip mounting read-write filesystem, will 
  be blank if copy-files-to-ram not set

- copy-base-filesystem-to-ram : copy existing flash to image to ram 
  unless an image file is already present in ram

These options are read from the /run/initramfs/init-options which is 
initialized from the combination of the kernel command line and 
the saved contents of two u-boot environment variables openbmcinit 
and openbmconce.  The file can be edited at the debug-init-sh prompt 
and/or via the shell command line stored in the debug hook.

A custom initramfs can be booted via tftp with an embedded image-rofs 
that will be activated for run.

I do not have a dhcp server to test setting variables from a dhcp script.

An example download command today might be:
u-boot env:

# set kernel command line with copy of static ip configuration (none). run addip
fw_setenv addip 'setenv bootargs ${bootargs} ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}:${hostname}:eth0:none:${dnsip}:${dnsip2}'

# init option via kernel command line for temporary host by "run triggerdownload"
fw_setenv triggerdownload "setenv bootargs ${bootargs} openbmc-init-download-files"

# an http get from dns resolved host
fw_setenv openbmcinitdownload 'cp /proc/net/pnp /run/resolv.conf ; ln -snf ../run/resolv.conf /etc/resolv.conf ; wget -O /run/image-rofs http://server.example.com/openbmc/test-image-rofs'

# a simple tftp to fixed numberic server
fw_setenv openbmcinitdownload 'tftp -r test-image-rofs -l /run/image-rofs -g 192.168.0.1'
---
at the u-boot prompt you can then run
run addip dodownload

Not implemented but on shortlist:

Make update script more strict / lenient / smart, allowing update or save 
of rwfs files during runtime while read only file system is running from 
flash, or writing read only file system image while read write file 
system is running from flash (possibly cleaned to white listed files on 
this boot).  Delayed because it needs to exclude bmc container update
in addition to 3 ways to specify mtd device to mount.

Modify update script to take list of images to update instead of finding 
files via wildcard would save creating empty updates to run white list 
functions and duplicate knowledge of where images to flash are located.openbmc-init-download-files

Add options to change runtime init (eg init= kernel command line), defer 
updates (flash_images_before_init=n), and force jffs2 options in boot.

Adding hook for running script(s) before runtime init run to setup files
before systemd.

Adding systemd unit to clear the run-once init options variable from 
u-boot environment.  The command is "fw_setenv openbmcbootonce" and it 
can run every boot as the shutdown script will trigger an update of the 
fw_env back to flash on shutdown if the file differs from the flash.