1SPDX-License-Identifier: GPL-2.0+ 2/* 3 * Copyright 2010-2011 Calxeda, Inc. 4 */ 5 6The 'pxe' commands provide a near subset of the functionality provided by 7the PXELINUX boot loader. This allows U-Boot based systems to be controlled 8remotely using the same PXE based techniques that many non U-Boot based servers 9use. 10 11Commands 12======== 13 14pxe get 15------- 16 syntax: pxe get 17 18 follows PXELINUX's rules for retrieving configuration files from a tftp 19 server, and supports a subset of PXELINUX's config file syntax. 20 21 Environment 22 ----------- 23 'pxe get' requires two environment variables to be set: 24 25 pxefile_addr_r - should be set to a location in RAM large enough to hold 26 pxe files while they're being processed. Up to 16 config files may be 27 held in memory at once. The exact number and size of the files varies with 28 how the system is being used. A typical config file is a few hundred bytes 29 long. 30 31 bootfile,serverip - these two are typically set in the DHCP response 32 handler, and correspond to fields in the DHCP response. 33 34 'pxe get' optionally supports these two environment variables being set: 35 36 ethaddr - this is the standard MAC address for the ethernet adapter in use. 37 'pxe get' uses it to look for a configuration file specific to a system's 38 MAC address. 39 40 pxeuuid - this is a UUID in standard form using lower case hexadecimal 41 digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses 42 it to look for a configuration file based on the system's UUID. 43 44 File Paths 45 ---------- 46 'pxe get' repeatedly tries to download config files until it either 47 successfully downloads one or runs out of paths to try. The order and 48 contents of paths it tries mirrors exactly that of PXELINUX - you can 49 read in more detail about it at: 50 51 http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux 52 53pxe boot 54-------- 55 syntax: pxe boot [pxefile_addr_r] 56 57 Interprets a pxe file stored in memory. 58 59 pxefile_addr_r is an optional argument giving the location of the pxe file. 60 The file must be terminated with a NUL byte. 61 62 Environment 63 ----------- 64 There are some environment variables that may need to be set, depending 65 on conditions. 66 67 pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied, 68 an environment variable named pxefile_addr_r must be supplied. This is 69 typically the same value as is used for the 'pxe get' command. 70 71 bootfile - typically set in the DHCP response handler based on the 72 same field in the DHCP respone, this path is used to generate the base 73 directory that all other paths to files retrieved by 'pxe boot' will use. 74 If no bootfile is specified, paths used in pxe files will be used as is. 75 76 serverip - typically set in the DHCP response handler, this is the IP 77 address of the tftp server from which other files will be retrieved. 78 79 kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will 80 store the kernel(or FIT image) and initrd it retrieves from tftp. These 81 locations will be passed to the bootm command to boot the kernel. These 82 environment variables are required to be set. 83 84 fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it 85 retrieves from tftp. The retrieval is possible if 'fdt' label is defined in 86 pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r' 87 will be passed to bootm command to boot the kernel. 88 89 fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm 90 command if it is set and 'fdt_addr_r' is not passed to bootm command. 91 92pxe file format 93=============== 94The pxe file format is nearly a subset of the PXELINUX file format; see 95http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line 96commands - global commands, and commands specific to labels. Lines begining 97with # are treated as comments. White space between and at the beginning of 98lines is ignored. 99 100The size of pxe files and the number of labels is only limited by the amount 101of RAM available to U-Boot. Memory for labels is dynamically allocated as 102they're parsed, and memory for pxe files is statically allocated, and its 103location is given by the pxefile_addr_r environment variable. The pxe code is 104not aware of the size of the pxefile memory and will outgrow it if pxe files 105are too large. 106 107Supported global commands 108------------------------- 109Unrecognized commands are ignored. 110 111default <label> - the label named here is treated as the default and is 112 the first label 'pxe boot' attempts to boot. 113 114menu title <string> - sets a title for the menu of labels being displayed. 115 116menu include <path> - use tftp to retrieve the pxe file at <path>, which 117 is then immediately parsed as if the start of its 118 contents were the next line in the current file. nesting 119 of include up to 16 files deep is supported. 120 121prompt <flag> - if 1, always prompt the user to enter a label to boot 122 from. if 0, only prompt the user if timeout expires. 123 124timeout <num> - wait for user input for <num>/10 seconds before 125 auto-booting a node. 126 127label <name> - begin a label definition. labels continue until 128 a command not recognized as a label command is seen, 129 or EOF is reached. 130 131Supported label commands 132------------------------ 133labels end when a command not recognized as a label command is reached, or EOF. 134 135menu default - set this label as the default label to boot; this is 136 the same behavior as the global default command but 137 specified in a different way 138 139kernel <path> - if this label is chosen, use tftp to retrieve the kernel 140 (or FIT image) at <path>. it will be stored at the address 141 indicated in the kernel_addr_r environment variable, and 142 that address will be passed to bootm to boot this kernel. 143 144append <string> - use <string> as the kernel command line when booting this 145 label. 146 147initrd <path> - if this label is chosen, use tftp to retrieve the initrd 148 at <path>. it will be stored at the address indicated in 149 the initrd_addr_r environment variable, and that address 150 will be passed to bootm. 151 152fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob 153 at <path>. it will be stored at the address indicated in 154 the fdt_addr_r environment variable, and that address will 155 be passed to bootm. 156 157fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob 158 relative to <path>. If the fdtfile environment variable 159 is set, <path>/<fdtfile> is retrieved. Otherwise, the 160 filename is generated from the soc and board environment 161 variables, i.e. <path>/<soc>-<board>.dtb is retrieved. 162 If the fdt command is specified, fdtdir is ignored. 163 164localboot <flag> - Run the command defined by "localcmd" in the environment. 165 <flag> is ignored and is only here to match the syntax of 166 PXELINUX config files. 167 168Example 169------- 170Here's a couple of example files to show how this works. 171 172------------/tftpboot/pxelinux.cfg/menus/base.menu----------- 173menu title Linux selections 174 175# This is the default label 176label install 177 menu label Default Install Image 178 kernel kernels/install.bin 179 append console=ttyAMA0,38400 debug earlyprintk 180 initrd initrds/uzInitrdDebInstall 181 182# Just another label 183label linux-2.6.38 184 kernel kernels/linux-2.6.38.bin 185 append root=/dev/sdb1 186 187# The locally installed kernel 188label local 189 menu label Locally installed kernel 190 append root=/dev/sdb1 191 localboot 1 192------------------------------------------------------------- 193 194------------/tftpboot/pxelinux.cfg/default------------------- 195menu include pxelinux.cfg/menus/base.menu 196timeout 500 197 198default linux-2.6.38 199------------------------------------------------------------- 200 201When a pxe client retrieves and boots the default pxe file, 202'pxe boot' will wait for user input for 5 seconds before booting 203the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin 204to be downloaded, and boot with the command line "root=/dev/sdb1" 205 206Differences with PXELINUX 207========================= 208The biggest difference between U-Boot's pxe and PXELINUX is that since 209U-Boot's pxe support is written entirely in C, it can run on any platform 210with network support in U-Boot. Here are some other differences between 211PXELINUX and U-Boot's pxe support. 212 213- U-Boot's pxe does not support the PXELINUX DHCP option codes specified 214 in RFC 5071, but could be extended to do so. 215 216- when U-Boot's pxe fails to boot, it will return control to U-Boot, 217 allowing another command to run, other U-Boot command, instead of resetting 218 the machine like PXELINUX. 219 220- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it 221 only uses U-Boot. 222 223- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX 224 does, only a simple text based menu using the commands described in 225 this README. With PXELINUX, it's possible to have a graphical boot 226 menu, submenus, passwords, etc. U-Boot's pxe could be extended to support 227 a more robust menuing system like that of PXELINUX's. 228 229- U-Boot's pxe expects U-Boot uimg's as kernels. Anything that would work 230 with the 'bootm' command in U-Boot could work with the 'pxe boot' command. 231 232- U-Boot's pxe only recognizes a single file on the initrd command line. It 233 could be extended to support multiple. 234 235- in U-Boot's pxe, the localboot command doesn't necessarily cause a local 236 disk boot - it will do whatever is defined in the 'localcmd' env 237 variable. And since it doesn't support a full UNDI/PXE stack, the 238 type field is ignored. 239 240- the interactive prompt in U-Boot's pxe only allows you to choose a label 241 from the menu. If you want to boot something not listed, you can ctrl+c 242 out of 'pxe boot' and use existing U-Boot commands to accomplish it. 243