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935109cd9e
Add support for scanning and applying extension board devicetree overlays during PXE boot. After loading the main board devicetree, the system now scans for available extension boards and applies their overlays automatically. This enables dynamic hardware configuration for systems with extension boards during boot scenarios which are using pxe_utils. Signed-off-by: Kory Maincent (TI.com) <kory.maincent@bootlin.com> Reviewed-by: Simon Glass <sjg@chromium.org>
351 lines
13 KiB
ReStructuredText
351 lines
13 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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Copyright 2010-2011 Calxeda, Inc.
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PXE Boot and extlinux.conf
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==========================
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The ``pxe`` commands provide a near subset of the functionality
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provided by the PXELINUX boot loader. This allows U-Boot based systems
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to be controlled remotely using the same PXE based techniques that
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many non U-Boot based servers use.
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The ``sysboot`` command and Extlinux boot method use the same file
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format as PXE boot for ``extlinux.conf``.
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Commands
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--------
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``pxe get``
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**Syntax:** ``pxe get``
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follows PXELINUX's rules for retrieving configuration files
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from a tftp server, and supports a subset of PXELINUX's config
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file syntax. It requires certain environment variables to be
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set, see the Environment section below.
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**File Paths**
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``pxe get`` repeatedly tries to download config files until it
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either successfully downloads one or runs out of paths to
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try. The order and contents of paths it tries mirrors exactly
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that of PXELINUX - you can 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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**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
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of the pxe file. The file must be terminated with a NUL byte.
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There are some environment variables that may need to be set,
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depending on conditions, see the Environment section below.
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``sysboot``
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**Syntax:** ``sysboot [-p] <interface> <dev[:part]> <ext2|fat|any> [addr] [filename]``
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Load and boot an ``extlinux.conf`` file from a local
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filesystem. Paths in the ``extlinux.conf`` file (kernel,
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initrd, FDT and overlays) will be interpreted within that
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filesystem.
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Example:
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``sysboot mmc 0.0:2 any ${pxefile_addr_r} /boot/extlinux.conf``
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Environment
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-----------
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``pxefile_addr_r``
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Should be set to a location in RAM large enough to hold pxe
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files while they're being processed. Up to 16 config files may
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be held in memory at once. The exact number and size of the
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files varies with how the system is being used. A typical
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config file is a few hundred bytes long. Required for ``pxe
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get``, for ``pxe boot`` if the optional argument
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``pxefile_addr_r`` is not supplied.
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``bootfile``
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Typically set in the DHCP response handler, required for ``pxe
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get``. For ``pxe boot``, this path is used to generate the
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base directory that all other paths to files retrieved by
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``pxe boot`` will use. If no bootfile is specified, paths used
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in pxe files will be used as is.
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``serverip``
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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
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retrieved. Required for ``pxe get``.
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``kernel_addr_r``, ``initrd_addr_r``
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Locations in RAM to store the kernel (or FIT image) and
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initrd. These locations will be passed to the ``bootm``
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command to boot the kernel. These environment variables are
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required to be set.
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``fdt_addr_r``
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Location in RAM to store the retrieved fdt blob. Retrieval is
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possible if ``fdt`` label is defined in pxe file and
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``fdt_addr_r`` is set. If retrieval is possible,
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``fdt_addr_r`` will be passed to ``bootm`` command to boot the
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kernel.
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``fdt_addr``
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Location of a fdt blob. ``fdt_addr`` will be passed to
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``bootm`` command if it is set and ``fdt_addr_r`` is not
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passed to bootm command.
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``fdtoverlay_addr_r``
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Location in RAM to temporarily store fdt overlay(s) before
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applying them to the fdt blob stored at
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``fdt_addr_r``. Required to use the ``fdtoverlays`` command in
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the PXE file.
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``extension_overlay_addr``
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Location in RAM to temporarily store extension fdt overlay(s)
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before applying them to the fdt blob stored at ``fdt_addr_r``.
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``pxe_label_override``
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Override label to be used, if exists, instead of the default
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label. This will allow consumers to choose a pxe label at
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runtime instead of having to prompt the user. If
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``pxe_label_override`` is set but does not exist in the pxe
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menu, pxe would fallback to the default label if given, and no
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failure is returned but rather a warning message.
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``ethaddr``
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This is the standard MAC address for the ethernet adapter in
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use. ``pxe get`` uses it to look for a configuration file
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specific to a system's MAC address.
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``pxeuuid``
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This is a UUID in standard form using lower case hexadecimal
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digits, for example,
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550e8400-e29b-41d4-a716-446655440000. ``pxe get`` uses it to
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look for a configuration file based on the system's UUID.
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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;
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see http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed
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of one line commands - global commands, and commands specific to
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labels. Lines beginning with # are treated as comments. White space
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between and at the beginning of 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>``
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The label named here is treated as the default and is the
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first label 'pxe boot' attempts to boot.
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``fallback <label>``
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The label named here is treated as a fallback option that may
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be attempted should it be detected that booting of the default
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has failed to complete, for example via U-Boot's boot count
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limit functionality.
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``menu title <string>``
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Sets a title for the menu of labels being displayed.
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``menu include <path>``
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Use tftp to retrieve the pxe file at ``<path>``, which is then
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immediately parsed as if the start of its contents were the
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next line in the current file. nesting of include up to 16
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files deep is supported.
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``prompt <flag>``
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If 1, always prompt the user to enter a label to boot from. If
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0, only prompt the user if timeout expires.
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``timeout <num>``
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Wait for user input for <num>/10 seconds before auto-booting a
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node.
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``label <name>``
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Begin a label definition. Labels continue until a command not
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recognized as a label command is seen, 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``
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set this label as the default label to boot; this is the same
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behavior as the global default command but specified in a
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different way
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``kernel <path>``
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If this label is chosen, use tftp to retrieve the kernel (or
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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
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kernel. 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 be passed to bootm with that address (see:
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doc/uImage.FIT/command_syntax_extensions.txt). It is useful
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for overlay selection in pxe file (see
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:doc:`./fit/overlay-fdt-boot`).
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``fdtoverlays <path> [...]``
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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
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variable, and then applied in the load order to the fdt blob
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stored at the address indicated in the ``fdt_addr_r``
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environment variable.
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``devicetree-overlay <path> [...]``
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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
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variable, and then applied in the load order to the fdt blob
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stored at the address indicated in the ``fdt_addr_r``
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environment variable. Alias for fdtoverlays.
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``kaslrseed``
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set this label to request random number from hwrng as kaslr seed.
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``append <string>``
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Use ``<string>`` as the kernel command line when booting this
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label. Environment variable references like ``${var}`` are
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substituted before boot.
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``initrd <path>``
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If this label is chosen, use tftp to retrieve the initrd at
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``<path>``. it will be stored at the address indicated in the
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``initrd_addr_r`` environment variable, and that address will
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be passed to ``bootm``. For FIT image, the initrd can be
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provided with the same value than kernel, including
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configuration:
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``<path>#<conf>[#<extra-conf[#...]]``
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In this case, ``kernel_addr_r`` is passed to ``bootm``.
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``fdt <path>``
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If this label is chosen, use tftp to retrieve the fdt blob at
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``<path>``. It will be stored at the address indicated in the
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``fdt_addr_r`` environment variable, and that address will be
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passed to ``bootm``. For FIT image, the device tree can be
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provided with the same value than kernel, including
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configuration:
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``<path>#<conf>[#<extra-conf[#...]]``
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In this case, ``kernel_addr_r`` is passed to ``bootm``.
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``devicetree <path>``
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If this label is chosen, use tftp to retrieve the fdt blob at
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``<path>``. it will be stored at the address indicated in the
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``fdt_addr_r`` environment variable, and that address will be
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passed to ``bootm``. Alias for fdt.
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``fdtdir <path>``
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If this label is chosen, use tftp to retrieve a fdt blob
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relative to ``<path>``. If the ``fdtfile`` environment
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variable is set, ``<path>/<fdtfile>`` is retrieved. Otherwise,
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the filename is generated from the ``soc`` and ``board``
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environment variables, i.e. ``<path>/<soc>-<board>.dtb`` is
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retrieved. If the ``fdt`` command is specified, ``fdtdir`` is
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ignored.
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``localboot <flag>``
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Run the command defined by ``localcmd`` in the
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environment. ``<flag>`` is ignored and is only here to match
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the syntax of 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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.. code-block::
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:caption: /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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.. code-block::
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:caption: /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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When a pxe client retrieves and boots the default pxe file, ``pxe
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boot`` will wait for user input for 5 seconds before booting the
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``linux-2.6.38`` label, which will cause
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``/tftpboot/kernels/linux-2.6.38.bin`` to be downloaded, and boot with
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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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