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69076dff22
This adds support for specifying FDT overlays in an extlinux/pxelinux
configuration file.
Without this, there is no simple way to apply overlays when the kernel
and fdt is loaded by the pxe command.
This change adds the 'fdtoverlays' keyword for a label, supporting multiple
overlay files to be applied on top of the fdt specified in the 'fdt' or
'devicetree' keyword.
Example:
label linux
kernel /Image
fdt /soc-board.dtb
fdtoverlays /soc-board-function.dtbo
append console=ttyS0,115200 root=/dev/mmcblk0p2 rootwait
This code makes usage of a new variable called fdtoverlay_addr_r used to load
the overlay files without overwritting anything important.
Cc: Tom Rini <trini@konsulko.com>
Cc: Andre Heider <a.heider@gmail.com>
Cc: Jernej Škrabec <jernej.skrabec@siol.net>
Cc: Jonas Karlman <jonas@kwiboo.se>
Tested-by: Jernej Škrabec <jernej.skrabec@siol.net>
Reviewed-by: Jernej Škrabec <jernej.skrabec@siol.net>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
259 lines
11 KiB
Plaintext
259 lines
11 KiB
Plaintext
SPDX-License-Identifier: GPL-2.0+
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/*
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* Copyright 2010-2011 Calxeda, Inc.
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*/
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The 'pxe' commands provide a near subset of the functionality provided by
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the PXELINUX boot loader. This allows U-Boot based systems to be controlled
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remotely using the same PXE based techniques that many non U-Boot based servers
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use.
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Commands
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========
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pxe get
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-------
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syntax: pxe get
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follows PXELINUX's rules for retrieving configuration files from a tftp
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server, and supports a subset of PXELINUX's config file syntax.
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Environment
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-----------
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'pxe get' requires two environment variables to be set:
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pxefile_addr_r - should be set to a location in RAM large enough to hold
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pxe files while they're being processed. Up to 16 config files may be
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held in memory at once. The exact number and size of the files varies with
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how the system is being used. A typical config file is a few hundred bytes
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long.
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bootfile,serverip - these two are typically set in the DHCP response
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handler, and correspond to fields in the DHCP response.
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'pxe get' optionally supports these two environment variables being set:
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ethaddr - this is the standard MAC address for the ethernet adapter in use.
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'pxe get' uses it to look for a configuration file specific to a system's
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MAC address.
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pxeuuid - this is a UUID in standard form using lower case hexadecimal
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digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses
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it to look for a configuration file based on the system's UUID.
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File Paths
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----------
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'pxe get' repeatedly tries to download config files until it either
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successfully downloads one or runs out of paths to try. The order and
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contents of paths it tries mirrors exactly that of PXELINUX - you can
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read in more detail about it at:
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http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
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pxe boot
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--------
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syntax: pxe boot [pxefile_addr_r]
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Interprets a pxe file stored in memory.
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pxefile_addr_r is an optional argument giving the location of the pxe file.
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The file must be terminated with a NUL byte.
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Environment
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-----------
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There are some environment variables that may need to be set, depending
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on conditions.
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pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied,
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an environment variable named pxefile_addr_r must be supplied. This is
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typically the same value as is used for the 'pxe get' command.
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bootfile - typically set in the DHCP response handler based on the
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same field in the DHCP respone, this path is used to generate the base
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directory that all other paths to files retrieved by 'pxe boot' will use.
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If no bootfile is specified, paths used in pxe files will be used as is.
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serverip - typically set in the DHCP response handler, this is the IP
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address of the tftp server from which other files will be retrieved.
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kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
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store the kernel(or FIT image) and initrd it retrieves from tftp. These
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locations will be passed to the bootm command to boot the kernel. These
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environment variables are required to be set.
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fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it
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retrieves from tftp. The retrieval is possible if 'fdt' label is defined in
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pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r'
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will be passed to bootm command to boot the kernel.
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fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm
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command if it is set and 'fdt_addr_r' is not passed to bootm command.
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fdtoverlay_addr_r - location in RAM at which 'pxe boot' will temporarily store
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fdt overlay(s) before applying them to the fdt blob stored at 'fdt_addr_r'.
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pxe file format
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===============
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The pxe file format is nearly a subset of the PXELINUX file format; see
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http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
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commands - global commands, and commands specific to labels. Lines begining
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with # are treated as comments. White space between and at the beginning of
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lines is ignored.
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The size of pxe files and the number of labels is only limited by the amount
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of RAM available to U-Boot. Memory for labels is dynamically allocated as
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they're parsed, and memory for pxe files is statically allocated, and its
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location is given by the pxefile_addr_r environment variable. The pxe code is
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not aware of the size of the pxefile memory and will outgrow it if pxe files
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are too large.
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Supported global commands
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-------------------------
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Unrecognized commands are ignored.
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default <label> - the label named here is treated as the default and is
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the first label 'pxe boot' attempts to boot.
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menu title <string> - sets a title for the menu of labels being displayed.
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menu include <path> - use tftp to retrieve the pxe file at <path>, which
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is then immediately parsed as if the start of its
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contents were the next line in the current file. nesting
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of include up to 16 files deep is supported.
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prompt <flag> - if 1, always prompt the user to enter a label to boot
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from. if 0, only prompt the user if timeout expires.
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timeout <num> - wait for user input for <num>/10 seconds before
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auto-booting a node.
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label <name> - begin a label definition. labels continue until
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a command not recognized as a label command is seen,
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or EOF is reached.
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Supported label commands
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------------------------
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labels end when a command not recognized as a label command is reached, or EOF.
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menu default - set this label as the default label to boot; this is
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the same behavior as the global default command but
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specified in a different way
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kernel <path> - if this label is chosen, use tftp to retrieve the kernel
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(or FIT image) at <path>. it will be stored at the address
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indicated in the kernel_addr_r environment variable, and
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that address will be passed to bootm to boot this kernel.
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For FIT image, The configuration specification can be
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appended to the file name, with the format:
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<path>#<conf>[#<extra-conf[#...]]
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It will passed to bootm with that address.
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(see: doc/uImage.FIT/command_syntax_extensions.txt)
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It useful for overlay selection in pxe file
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(see: doc/uImage.FIT/overlay-fdt-boot.txt)
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fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT
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overlay(s) at <path>. it will be temporarily stored at the
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address indicated in the fdtoverlay_addr_r environment variable,
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and then applied in the load order to the fdt blob stored at the
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address indicated in the fdt_addr_r environment variable.
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append <string> - use <string> as the kernel command line when booting this
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label.
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initrd <path> - if this label is chosen, use tftp to retrieve the initrd
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at <path>. it will be stored at the address indicated in
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the initrd_addr_r environment variable, and that address
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will be passed to bootm.
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fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob
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at <path>. it will be stored at the address indicated in
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the fdt_addr_r environment variable, and that address will
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be passed to bootm.
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fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob
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relative to <path>. If the fdtfile environment variable
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is set, <path>/<fdtfile> is retrieved. Otherwise, the
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filename is generated from the soc and board environment
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variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
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If the fdt command is specified, fdtdir is ignored.
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localboot <flag> - Run the command defined by "localcmd" in the environment.
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<flag> is ignored and is only here to match the syntax of
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PXELINUX config files.
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Example
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-------
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Here's a couple of example files to show how this works.
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------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
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menu title Linux selections
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# This is the default label
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label install
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menu label Default Install Image
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kernel kernels/install.bin
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append console=ttyAMA0,38400 debug earlyprintk
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initrd initrds/uzInitrdDebInstall
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# Just another label
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label linux-2.6.38
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kernel kernels/linux-2.6.38.bin
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append root=/dev/sdb1
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# The locally installed kernel
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label local
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menu label Locally installed kernel
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append root=/dev/sdb1
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localboot 1
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-------------------------------------------------------------
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------------/tftpboot/pxelinux.cfg/default-------------------
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menu include pxelinux.cfg/menus/base.menu
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timeout 500
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default linux-2.6.38
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-------------------------------------------------------------
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When a pxe client retrieves and boots the default pxe file,
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'pxe boot' will wait for user input for 5 seconds before booting
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the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
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to be downloaded, and boot with the command line "root=/dev/sdb1"
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Differences with PXELINUX
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=========================
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The biggest difference between U-Boot's pxe and PXELINUX is that since
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U-Boot's pxe support is written entirely in C, it can run on any platform
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with network support in U-Boot. Here are some other differences between
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PXELINUX and U-Boot's pxe support.
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- U-Boot's pxe does not support the PXELINUX DHCP option codes specified
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in RFC 5071, but could be extended to do so.
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- when U-Boot's pxe fails to boot, it will return control to U-Boot,
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allowing another command to run, other U-Boot command, instead of resetting
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the machine like PXELINUX.
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- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
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only uses U-Boot.
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- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
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does, only a simple text based menu using the commands described in
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this README. With PXELINUX, it's possible to have a graphical boot
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menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
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a more robust menuing system like that of PXELINUX's.
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- U-Boot's pxe expects U-Boot uimg's as kernels. Anything that would work
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with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
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- U-Boot's pxe only recognizes a single file on the initrd command line. It
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could be extended to support multiple.
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- in U-Boot's pxe, the localboot command doesn't necessarily cause a local
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disk boot - it will do whatever is defined in the 'localcmd' env
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variable. And since it doesn't support a full UNDI/PXE stack, the
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type field is ignored.
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- the interactive prompt in U-Boot's pxe only allows you to choose a label
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from the menu. If you want to boot something not listed, you can ctrl+c
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out of 'pxe boot' and use existing U-Boot commands to accomplish it.
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