diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/README.pxecfg | 239 |
1 files changed, 239 insertions, 0 deletions
diff --git a/doc/README.pxecfg b/doc/README.pxecfg new file mode 100644 index 000000000..5c5f8c7f6 --- /dev/null +++ b/doc/README.pxecfg @@ -0,0 +1,239 @@ +/* + * Copyright 2010-2011 Calxeda, Inc. + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License as published by the Free + * Software Foundation; either version 2 of the License, or (at your option) + * any later version. + * + * This program is distributed in the hope it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for + * more details. + * + * You should have received a copy of the GNU General Public License along with + * this program. If not, see <http://www.gnu.org/licenses/>. + */ + +The pxecfg commands provide a near subset of the functionality provided by +the PXELINUX boot loader. This allows U-boot based systems to be controlled +remotely using the same PXE based techniques that many non U-boot based servers +use. To avoid identity confusion with PXELINUX, and because not all behavior is +identical, we call this feature 'pxecfg'. + +Commands +======== + +pxecfg get +---------- + syntax: pxecfg get + + follows PXELINUX's rules for retrieving configuration files from a tftp + server, and supports a subset of PXELINUX's config file syntax. + + Environment + ----------- + get_pxecfg requires two environment variables to be set: + + pxecfg_ram - should be set to a location in RAM large enough to hold + pxecfg files while they're being processed. Up to 16 config files may be + held in memory at once. The exact number and size of the files varies with + how the system is being used. A typical config file is a few hundred bytes + long. + + bootfile,serverip - these two are typically set in the DHCP response + handler, and correspond to fields in the DHCP response. + + get_pxecfg optionally supports these two environment variables being set: + + ethaddr - this is the standard MAC address for the ethernet adapter in use. + getpxe_cfg uses it to look for a configuration file specific to a system's + MAC address. + + pxeuuid - this is a UUID in standard form using lower case hexadecimal + digits, for example, 550e8400-e29b-41d4-a716-446655440000. get_pxecfg uses + it to look for a configuration file based on the system's UUID. + + File Paths + ---------- + get_pxecfg repeatedly tries to download config files until it either + successfully downloads one or runs out of paths to try. The order and + contents of paths it tries mirrors exactly that of PXELINUX - you can read + in more detail about it at: + + http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux + +pxecfg boot +----------- + syntax: pxecfg boot [pxecfg_addr] + + Interprets a pxecfg file stored in memory. + + pxecfg_addr is an optional argument giving the location of the pxecfg file + + Environment + ----------- + There are some environment variables that may need to be set, depending on + conditions. + + pxecfg_ram - if the optional argument pxecfg_addr is not supplied, an + environment variable named pxecfg_ram must be supplied. This is typically + the same value as is used for the get_pxecfg command. + + bootfile - typically set in the DHCP response handler based on the same + field in the DHCP respone, this path is used to generate the base directory + that all other paths to files retrieved by boot_pxecfg will use. + + serverip - typically set in the DHCP response handler, this is the IP + address of the tftp server from which other files will be retrieved. + + kernel_ram,initrd_ram - locations in RAM at which boot_pxecfg will store + the kernel and initrd it retrieves from tftp. These locations will be + passed to the bootm command to boot the kernel. These environment variables + are required to be set. + + fdtaddr - the location of a fdt blob. If this is set, it will be passed to + bootm when booting a kernel. + +pxecfg file format +================== +The pxecfg file format is more or less a subset of the PXELINUX file format, see +http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line +commands - global commands, and commands specific to labels. Lines begining with +# are treated as comments. White space between and at the beginning of lines is +ignored. + +The size of pxecfg files and the number of labels is only limited by the amount +of RAM available to U-boot. Memory for labels is dynamically allocated as +they're parsed, and memory for pxecfg files is statically allocated, and its +location is given by the pxecfg_ram environment variable. the pxecfg code is +not aware of the size of the pxecfg memory and will outgrow it if pxecfg files +are too large. + +Supported global commands +------------------------- +Unrecognized commands are ignored. + +default <label> - the label named here is treated as the default and is + the first label boot_pxecfg attempts to boot. + +menu title <string> - sets a title for the menu of labels being displayed. + +menu include <path> - use tftp to retrieve the pxecfg file at <path>, which + is then immediately parsed as if the start of its + contents were the next line in the current file. nesting + of include up to 16 files deep is supported. + +prompt <flag> - if 1, always prompt the user to enter a label to boot + from. if 0, only prompt the user if timeout expires. + +timeout <num> - wait for user input for <num>/10 seconds before + auto-booting a node. + +label <name> - begin a label definition. labels continue until + a command not recognized as a label command is seen, + or EOF is reached. + +Supported label commands +------------------------ +labels end when a command not recognized as a label command is reached, or EOF. + +menu default - set this label as the default label to boot; this is + the same behavior as the global default command but + specified in a different way + +kernel <path> - if this label is chosen, use tftp to retrieve the kernel + at <path>. it will be stored at the address indicated in + the kernel_ram environment variable, and that address + will be passed to bootm to boot this kernel. + +append <string> - use <string> as the kernel command line when booting this + label. + +initrd <path> - if this label is chosen, use tftp to retrieve the initrd + at <path>. it will be stored at the address indicated in + the initrd_ram environment variable, and that address + will be passed to bootm. + +localboot <flag> - Run the command defined by "localcmd" in the environment. + <flag> is ignored and is only here to match the syntax of + PXELINUX config files. + +Example +------- +Here's a couple of example files to show how this works. + +------------/tftpboot/pxelinux.cfg/menus/linux.list---------- +menu title Linux selections + +# This is the default label +label install + menu label Default Install Image + kernel kernels/install.bin + append console=ttyAMA0,38400 debug earlyprintk + initrd initrds/uzInitrdDebInstall + +# Just another label +label linux-2.6.38 + kernel kernels/linux-2.6.38.bin + append root=/dev/sdb1 + +# The locally installed kernel +label local + menu label Locally installed kernel + append root=/dev/sdb1 + localboot 1 +------------------------------------------------------------- + +------------/tftpboot/pxelinux.cfg/default------------------- +menu include pxelinux.cfg/menus/base.menu +timeout 500 + +default linux-2.6.38 +------------------------------------------------------------- + +When a pxecfg client retrieves and boots the default pxecfg file, +boot_pxecfg will wait for user input for 5 seconds before booting +the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin +to be downloaded, and boot with the command line "root=/dev/sdb1" + +Differences with PXELINUX +========================= +The biggest difference between pxecfg and PXELINUX is that since pxecfg +is part of U-boot and is written entirely in C, it can run on platform +with network support in U-boot. Here are some of the other differences +between PXELINUX and pxecfg. + +- pxecfg does not support the PXELINUX DHCP option codes specified in + RFC 5071, but could be extended to do so. + +- when pxecfg fails to boot, it will return control to U-boot, allowing + another command to run, other U-boot command, instead of resetting the + machine like PXELINUX. + +- pxecfg doesn't rely on or provide an UNDI/PXE stack in memory, it only + uses U-boot. + +- pxecfg doesn't provide the full menu implementation that PXELINUX + does, only a simple text based menu using the commands described in + this README. With PXELINUX, it's possible to have a graphical boot + menu, submenus, passwords, etc. pxecfg could be extended to support + a more robust menuing system like that of PXELINUX's. + +- pxecfg expects U-boot uimg's as kernels. anything that would work with + the 'bootm' command in U-boot could work with pxecfg. + +- pxecfg doesn't recognize initrd options in the append command - you must + specify initrd files using the initrd command + +- pxecfg only recognizes a single file on the initrd command line. it + could be extended to support multiple + +- in pxecfg, the localboot command doesn't necessarily cause a local + disk boot - it will do whatever is defined in the 'localcmd' env + variable. And since it doesn't support a full UNDI/PXE stack, the + type field is ignored. + +- the interactive prompt in pxecfg only allows you to choose a label from + the menu. if you want to boot something not listed, you can ctrl+c out + of pxecfg and use existing U-boot commands to accomplish it. |