TFTP Boot and NFS Root Filesystems

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How To Set Up TFTP Boot And NFS Root Filesystems On Parallella

This Guide describes how to set up the Parallella U-Boot to network boot using TFTP.
Also, it describes how to set up mounting a root filesystem (rootfs) via NFS, so that a Parallella is run as a 'Thick Client'.
For background to the TFTP Boot in U-Boot, see the Manual for Das U-Boot
The following is based on the original blog post by Scott Johnson describing how to set up a Parallella cluster to use TFTP/NFS, but has been tweaked - mainly to minimise the need to edit/update the U-Boot variables via the Serial/UART cable, and provide more flexibility by using PC-based editors and storage.

By editing a bootscript on the TFTP server (and re-booting), a Parallella can be re-configured to a different boot mode (headless,HDMI) and/or different root filesystem (Ubuntu, Debian, nano) - all without having to 'burn' another Parallella SD card (perhaps ever..?).
Alternative root filesystems: A Parallella may have alternative Linux root filesystems, holding different configurations or versions. The alternative root filesystems (e.g. Ubuntu, Linaro Nano, with/without SDK) are just like 'burning' and booting from multiple SD cards.
Shared root filesystems: A root filesystem directory on the NFS server may also be shared by a number of Parallellas, say, in a cluster. The many advantages include saving space on the server, and mainly(!) not having to replicate SD cards for each cluster member.
Cloning and modifying the NFS directories for use by other Parallellas is also easier and quicker: just copy directories on the NFS Server (and perhaps edit a couple of files).
Tweak the example below to suit your needs.

Requirements

Linux PC, Parallella board(s), USB to Serial (TTL/UART) adapter, DHCP server.

Summary

This Guide describes:

  • An IP addressing and naming scheme using DHCP to support different boot modes (headless, HDMI) and NFS root filesystems.
  • Setting up TFTP and a directory layout for TFTP bootscripts and boot mode image files.
  • Changing the way the boot arguments are passed to the kernel, i.e. in the U-Boot 'bootargs' rather than devicetree.
  • Setting up NFS and a directory layout for NFS root filesystems, allowing a choice of root filesystems for each Parallella.
  • Changing the U-Boot boot command to fetch a small bootscript file using TFTP.
  • An example bootscript for TFTP boot and NFS root filesystem.
  • Use of mkimage to convert the bootscript text file into a U-Boot script image file.
  • A breakdown of the bootscript to show different options.

IMPORTANT NOTE:

  • {Sept 2014} There is a problem in Parallella U-Boot w.r.t. the Ethernet interface after any network activity in U-Boot (e.g. TFTP). (See the post on the Parallella forum post by tajama). The ethernet interface is left in an unuseable state. A workaround is included in the script example below; but before attempting to apply it - you MUST check the U-Boot version. (Revisit)
  • {Sept 2014} the Parallella U-Boot is being updated which just might affect the script below. (Revisit).


Set up IP Addresses Using DHCP

Allocate IP addresses for the Parallella(s) and the TFTP/NFS servers in your DHCP server based on MAC address. The Parallella MAC address is printed on the board, and is also a U-Boot variable (see later).
Refer to the documentation of your DHCP server, or discuss with your network admin.
The IP addresses are used as follows:

  • U-Boot tftpboot command requests a bootscript file, and needs the TFTP server IP address <serverip>, and its own IP address <ipaddr>.
  • U-Boot tells Linux to use DHCP.
  • The NFS server uses IP addresses to control access to the exported rootfs directories.

This is an example IP address allocation and naming convention (your network may vary):

192.168.1.21	para1		// <ipaddr> IP address of Parallella "para"<n>
192.168.1.22	para2
...
192.168.1.28	para8     	// ... I wish :)
192.168.1.50	TFTP server	// IP address of TFTP server "serverip"
192.168.1.50	NFS server	// IP address of NFS server "nfs_ip"

Note: The TFTP and NFS services do not need to be on the same physical server, or even the same operating system. A Debian (Wheezy) PC provides both services in this example.

TFTP Server

Prepare the TFTP Service

Get the required software if not already set up. On Debian:

apt-get install tftpd-hpa

The TFTP service does not start automatically.
(Note: There are a number of examples in various forums, etc, of how to automatically start the TFTP service - but not all are successful on all Linux distro's it seems! The following may work for you.)
Start the tftpd-hpa service automatically by adding a command to /etc/rc.local (just before the exit 0 line).

sudo nano /etc/rc.local

(Edit and save)

service tftpd-hpa start

To control the TFTP service from the command line use:

sudo service tftpd-hpa restart	// to restart, or use 'stop', or 'start' as needed.

To check the status of the TFTP service from the command line use:

sudo service tftpd-hpa status
[ ok ] in.tftpd is running.     	     	// Service is Up
[FAIL] in.tftpd is not running ... failed!     	// Service is Down

Set up the TFTP Directories

By default, the tftpd-hpa service looks for requested files under /srv/tftp/.
Each Parallella has its own bootscript, e.g. para1, para2, in the TFTP service directory. The bootscript is a U-Boot script image file, created using mkimage from a text file (see below).
The bootscript points U-Boot to a boot mode sub-directory holding the boot image files.
Each boot mode directory is the equivalent of the BOOT partition on a Parallella SD card, containing the kernel, parallella.bit.bin and devicetree image files.
Different sets of boot image files may be held in different directories, e.g. headless_7010, hdmi_7010, test_new_kernel. By pointing at a different directory, the bootscript controls how the Parallella will be booted.
Note: only needs one directory per boot mode - not one per Parallella.
The bootscript provides U-Boot with the TFTP commands to load the image files and to boot the kernel.
The bootscript also provides the Linux boot parameters (bootargs) to mount the NFS root filesystem.

Create a Boot Mode Directory and Prepare the Image Files

sudo mkdir -p /srv/tftp/<name>		// replace <name> with boot mode, e.g. hdmi_7010

Follow the instructions for creating the SD card (download, extract and rename the kernel uImage, parallella.bit.bin and devicetree.dtb files) but instead of 'burning' to a SD card simply copy the image files to the boot mode directory (as root).
The TFTP service directory layout (for this example) will look something like:

/svr/tftp/				// TFTP service directory
	hdmi_7010/			// boot mode = Zynq 7010 with HDMI support
		paralella.bit.bin
		devicetree.dtb
		uImage
	headless_7010/			// boot mode = Zynq 7010 Parallella configured as headless
		paralella.bit.bin
		devicetree.dtb
		uImage
	test_new_kernel/		// boot mode = temp testing variation
		paralella.bit.bin
		devicetree.dtb
		uImage
	para1			        // bootscript for para1
	para2			        // bootscript for para2
	...
	para8			        // bootscript for para8, etc

Note: The image files follow the same naming convention as for SD card booting.

Remove Bootargs from Devicetree

The Parallella devicetrees, as supplied by Adapteva, pass the boot arguments to support booting from the SD card. Instead, the boot arguments are passed to the kernel by U-Boot, as defined in the bootscript (see below). The devicetree image files need to be edited to remove the boot commands.
Install the devicetree compiler if not already installed. On Debian:

sudo apt-get install device-tree-compiler

Extract/edit/rebuild the devicetree.dtb file to remove the parameters from the chosen {} branch. Repeat for all supplied devicetree.dtb files in each boot mode directory.

cd /srv/tftp/<name>		// replace <name> with boot mode, e.g. hdmi_7010
sudo dtc -I dtb -o dev.dts -O dts devicetree.dtb
sudo nano dev.dts

Look for the chosen { } branch, remove the main 'bootargs' arguments, and save.

	chosen {
		linux,stdout-path = "/amba@0/uart@E0001000";
	};

Recompile the devicetree.dtb and delete the dev.dts text file.

sudo dtc -I dts -O dtb -o devicetree.dtb dev.dts
sudo rm dev.dts

NFS Server

The Official (and Unofficial) sources of Linux root filesystems for the Parallella provide instructions for extracting and 'burning' the contents to SD card. The instructions are then repeated for each physical SD card required for each Parallella in a cluster. Similar steps need to be taken to create the root filesystem contents of the NFS mounted directories - but the process is (usually) much quicker and more flexible.
Some minor edits to the configuration files are usually needed to ensure that the NFS variant works smoothly in a network environment. The NFS directories are available for viewing (and editing) on the NFS Server host.
Once fully set up and running, the root filesystem will need to be managed and maintained as normal, (e.g. sudo apt-get update). This needs to be done within a session on (one of) the Parallella using:

  • the USB serial console which provides a root session, or
  • a remote SSH session after the ssh-server has been set up on the Parallella, or
  • a keyboard, mouse, screen if the Parallella has been booted with HDMI support.

Note: If the root filesystem is shared then this maintenance only needs to be carried on one Parallella (and not for each SD card).
IMPORTANT WARNING:
When editing configuration files in the NFS root filesystem directories on the NFS Server host using root permissions:

  • Avoid the mistake of editing your host PC's configuration!
  • Make Sure You Are In The Correct NFS Sub-directory!


Prepare the NFS Service

Get the required software if not already set up. On Debian:

apt-get install nfs-kernel-server

The NFS service starts automatically. To control NFS services use:

sudo service nfs-kernel-server restart		// to restart, or use 'stop', or 'start' as needed.

To check the status of the NFS service from the command line use:

sudo service nfs-kernel-server status
nfsd running          	// Service is Up
nfsd not running     	// Service is Down

Set up the NFS Directories

Create a top directory /srv/nfs, and create a subdirectory under that for each NFS mounted root filesystem required.
Here are some examples of NFS filesystem directories, including shared root filesystems, and where a Parallella may have a choice of root filesystems.
In this example, para1 is the only Parallella with HDMI/USB connected; the other cluster members are headless 7010's running, say, nano. For work using the SDK version, para1 is booted with HDMI support and mounts the ubuntu_SDK root filesystem, otherwise, para1 is booted (after changing the bootscript) with the headless images and nano.

sudo mkdir -p /srv/nfs
sudo mkdir -p /srv/nfs/ubuntu		// rootfs based on standard Parallella Ubuntu build, to be shared by all cluster members (including para1)
sudo mkdir -p /srv/nfs/nano		// rootfs based on a slim linaro nano build, to be shared by all cluster members (including para1)
sudo mkdir -p /srv/nfs/ubuntu_SDK	// rootfs based on Parallella Ubuntu build, with latest SDK (to be used by para1 only).
sudo mkdir -p /srv/nfs/nano_X_server	// rootfs based on a linaro nano build with SDK, X server (to be used by para1 only).

Set up Contents of the Parallella NFS Root Filesystems

Instead of 'burning' a Linux root filesystem image to a partition on the SD card, place the payload root filesystem in the NFS directory, e.g. /srv/nfs/ubuntu/.
Each source of root filesystem may involve slightly different preparation to enable the NFS root filesystem to work smoothly.
See the example in the How-to set up Linaro Nano Root Filesystem for NFS Boot

Update NFS Exports File

The NFS server requires /etc/exports to be configured correctly, to control access to each NFS filesystem directory to specific hosts. In this case the hosts are identified by their IP address.
For each Parallella root filesystem that is created, add the export control line to /etc/exports, adjusting (as you should for all examples herein) for your local IP address and directory naming scheme. The following is an example based on the layout described above. Note:

  • Where multiple hosts share an exported directory, the "hostIP(attributes)" are separated by <space>.
  • There is no <space> between "hostIP" and "(attributes)".
  • Continuation lines may be used for clarity. Continuation is "<space>\" only (i.e. no hidden tabs, etc).
sudo nano /etc/exports

(Edit and save)

/srv/nfs/ubuntu 192.168.1.21(rw,sync,no_root_squash,no_subtree_check) \
192.168.1.22(rw,sync,no_root_squash,no_subtree_check) \
192.168.1.23(rw,sync,no_root_squash,no_subtree_check) \
192.168.1.24(rw,sync,no_root_squash,no_subtree_check)
/srv/nfs/ubuntu_SDK 192.168.1.21(rw,sync,no_root_squash,no_subtree_check)
/srv/nfs/nano 192.168.1.21(rw,sync,no_root_squash,no_subtree_check) \
192.168.1.22(rw,sync,no_root_squash,no_subtree_check) \
192.168.1.23(rw,sync,no_root_squash,no_subtree_check) \
192.168.1.24(rw,sync,no_root_squash,no_subtree_check)
/srv/nfs/nano_X_server 192.168.1.22(rw,sync,no_root_squash,no_subtree_check)

Note: The bootscript ensures that only one of the optional filesystems will be accessed/mounted at any one time by a Parallella on a re-boot.

Export the NFS Directories

Ensure that these directories are made visible by the NFS service. Either:

sudo exportfs -a

or

sudo service nfs-kernel-server restart



Parallella TFTP Boot

The default U-Boot boot sequence looks for the boot image files on the SD card. The boot command is modified to load a bootscript using the built-in TFTP boot command.

Set Up the Parallella to TFTP Boot

Power off the Parallella and remove the ethernet, USB peripheral and HDMI cables and SD card.
Connect a USB serial cable to the 3-pin UART header on the Parallella. An example device from Adafruit, and see connecting a UART serial cable to the Parallella
On the PC, use a terminal program (e.g. screen, minicom) to connect to the UART Serial device. On minicom, set hardware flow control to off, and point the logfile to, say, ~/minicomlog' for diagnostics.
Power up the Parallella.
After the boot failure messages, you should get the zynq-uboot> prompt in the terminal window.
Display a list of the current state of the U-Boot environment variables using the printenv command.
Check the value of the ethaddr=xx:xx:xx:xx:xx:xx variable; this should be the same as the label on the board, and the MAC address you are using for this Parallella in your DHCP server.
Enter the following commands at the zynq-uboot> prompt in order to:

  • set the hostname variable which will be used as the bootscript name. Change for each Parallella.
  • set the IP address of the Parallella and the TFTP server. Change for each Parallella.
  • set the Ip address of the TFTP server. Usually the same for all Parallellas.
  • create a variable t-boot which contains the commands to fetch and then execute the bootscript.
  • change the U-Boot bootcmd so that it will run the t-boot TFTP boot sequence, only if no SD card is present.
setenv hostname para1
setenv ipaddr 192.168.1.21
setenv serverip 192.168.1.50
setenv t-addr 0x100000
setenv t-boot 'tftpboot ${t-addr} ${hostname} ; source ${t-addr}'
setenv bootcmd 'run modeboot ; run t-boot'

Trying - and failing - to find an SD card will add a few seconds to the boot sequence, but this is a useful fall-back. Optionally, to go straight to tftp boot, replace the bootcmd above with the following:

setenv bootcmd 'run t-boot'

Check that the variables have been set correctly, using printenv command, and save to flash memory, using saveenv command. Power off.
Reconnect the ethernet cable and any USB peripherals or HDMI you intend to use on the Parallella.
Ready to TFTP boot.
Notes:

  • It's worthwhile checking (again) after a power recycle that the U-Boot variables have been set correctly
  • To correct/change a variable, use the setenv command with new/correct value.
  • To remove a variable e.g. 'badvarible', use the setenv command with no value, e.g. setenv badvarible
  • U-Boot autocompletes commands so print, set, save will also work.


Parallella Bootscript

Writing a Parallella Bootscript

On the TFTP server host, the bootscript image file is initially created and edited as a text file, and compiled into a U-Boot executable image using mkimage.

Create a working directory to hold the bootscript text file(s).

mkdir ~/Documents/bootscr

Create a text file and copy/paste the text below as a template. The following is an example bootscript which is described below. This loads the headless image files for a 7010, and will load the shared linaro nano root filesystem.

cd ~/Documents/bootscr
nano para1.txt

(Edit and save)

setenv tftp_dir headless_7010
setenv nfs_rfs /srv/tftp/nano

setenv bootargs ip=dhcp
setenv bootargs ${bootargs} console=ttyPS0,115200

setenv nfs_ip 192.168.1.50
setenv bootargs ${bootargs} root=/dev/nfs rw nfsroot=${nfs_ip}:${nfs_rfs}

setenv fpga_image parallella.bit.bin
setenv fpga_addr 0x4000000
setenv fpga_size 0x3dbafc
setenv fpga_tftp 'tftpboot ${fpga_addr} ${tftp_dir}/${fpga_image}'
setenv fpga_load 'fpga load 0 ${fpga_addr} ${fpga_size}'

setenv fdt_image devicetree.dtb
setenv fdt_addr 0x2A00000
setenv fdt_tftp 'tftpboot ${fdt_addr} ${tftp_dir}/${fdt_image}'

setenv kernel_image uImage
setenv kernel_addr 0x3000000
setenv kernel_tftp 'tftpboot ${kernel_addr} ${tftp_dir}/${kernel_image}'

setenv phy_rst 'mw.w f8000008 df0d ; mw.w f8000140 00100801 ; mw.w f8000004 767b'
setenv rset_phy 'run phy_rst'

setenv boot_now 'bootm ${kernel_addr} - ${fdt_addr}'

run fpga_tftp fpga_load kernel_tftp fdt_tftp rset_phy boot_now

Copy the file to create a bootscript for each Parallella, changing the filename, e.g. para2.txt. Edit the values of the tftp_dir and nfs_rfs variables in each file as required. If the boot mode is the same and the NFS rootfs is shared, then there are usually no edits required.
To change the mode of a Parallella boot, edit the 'paraX.txt' file to change the tftp_dir and/or nfs_rfs variables, before re-making the image.
The directory structure on the Debian PC will then look something like this:

/home/{username}/Documents/bootscr/   	
      para1.txt	
      para2.txt
      ...
      para8.txt

Make the Bootscript Image

Install mkimage, which is part of the Das U-Boot tool-set, if not already installed. On Debian:

sudo apt-get install u-boot-tools

Convert each bootscript text file into a loadable image by mkimage, and place each image in the TFTP server directory. For example:

cd ~/Documents/bootscr
sudo mkimage -A arm -O u-boot -T script -C none -a 0 -e 0 -n "t-Boot Script" -d para1.txt /srv/tftp/para1
sudo mkimage -A arm -O u-boot -T script -C none -a 0 -e 0 -n "t-Boot Script" -d para2.txt /srv/tftp/para2
...
sudo mkimage -A arm -O u-boot -T script -C none -a 0 -e 0 -n "t-Boot Script" -d para8.txt /srv/tftp/para8

Reboot the Parallella

Reboot by power off, wait a few seconds, power on.
The output to the UART Serial terminal screen shows initialisation of the board and network, and then the boot sequence looking for the TFTP server.
If the TFTP 'Loading:' line puts out a few 'T T T's, then it's retrying. Give it a few moments but if there's a line of 'T's then check that the TFTP service is actually running, and that the IP addresses and filename of the bootscript are valid.
Once the small (~1kb) bootscript has been loaded and is executed by U-Boot, further TFTP requests will be seen as the image files are downloaded before U-Boot hands over to the kernel.

Breakdown of the Bootscript

This section takes the bootscript example and breaks it down to illustrate what may be changed to support your local environment.

  • Set up the bootscript to point to the required boot mode (i.e. TFTP sub-directory) and the NFS filesystem directory chosen for this Paralella. By editing these first two lines, a Parallella can be re-booted using a different FPGA, kernel and/or a different NFS root filesystem. Note that the the NFS filepath is the same as the line in NFS exports.
setenv tftp_dir headless_7010	   	      // or, hdmi_7010, etc
setenv nfs_rootfs /srv/nfs/nano	   	      // or /srv/nfs/nano_sdk, etc
  • Set the initial bootargs string to tell the kernel to use DHCP when loaded.
setenv bootargs ip=dhcp
  • Add the console argument to the bootargs string. If the console is not required, delete this line.
setenv bootargs ${bootargs} console=ttyPS0,115200
  • Add the NFS boot arguments to the bootargs string. Note the NFS server IP variable is not the same as the TFTP serverip variable, although they may have the same value.
setenv nfs_ip 192.168.1.50
setenv bootargs ${bootargs} root=/dev/nfs rw nfsroot=${nfs_ip}:${nfs_rfs}
  • If required, add additional kernel boot diagnostic flags to the bootargs string. If not required, delete this line.
setenv bootargs ${bootargs} nfsrootdebug earlyprintk
  • Set up the variables for the command to tftpboot the fpga image, and the command to load the image into the fpga.
setenv fpga_image parallella.bit.bin
setenv fpga_addr 0x4000000
setenv fpga_size 0x3dbafc
setenv fpga_tftp 'tftpboot ${fpga_addr} ${tftp_dir}/${fpga_image}'
setenv fpga_load 'fpga load 0 ${fpga_addr} ${fpga_size}'
  • Set up the variables for the command to tftpboot the devicetree image.
setenv fdt_image devicetree.dtb
setenv fdt_addr 0x2A00000
setenv fdt_tftp 'tftpboot ${fdt_addr} ${tftp_dir}/${fdt_image}'
  • Set up the variables for the command to tftpboot the kernel image.
setenv kernel_image uImage
setenv kernel_addr 0x3000000
setenv kernel_tftp 'tftpboot ${kernel_addr} ${tftp_dir}/${kernel_image}'
  • Patch U-Boot network handling. This is a workround for the problem identified by tajama, and referred to above. It MAY apply to your version but YOU MUST CHECK!! This U-Boot patch applies to the following version, which is output initially by U-Boot:
U-Boot 2012.10-00003-g792c31c (Jan 03 2014 - 12:24:08)
setenv phy_rst 'mw.w f8000008 df0d ; mw.w f8000140 00100801 ; mw.w f8000004 767b'
setenv rset_phy 'run phy_rst'
  • Set up the variable for the command to boot into the kernel, passing the kernel and devicetree image addresses.
setenv boot_now 'bootm ${kernel_addr} - ${fdt_addr}'
  • Finally, run the sequence of individual commands and boot. If any of the command sequence fails, then the 'run' command will halt. Note there are no ';' separators in the command parameters.
run fpga_tftp fpga_load kernel_tftp fdt_tftp rset_phy boot_now