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 92 fdtoverlay_addr_r - location in RAM at which 'pxe boot' will temporarily store 93 fdt overlay(s) before applying them to the fdt blob stored at 'fdt_addr_r'. 94 95pxe file format 96=============== 97The pxe file format is nearly a subset of the PXELINUX file format; see 98http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line 99commands - global commands, and commands specific to labels. Lines begining 100with # are treated as comments. White space between and at the beginning of 101lines is ignored. 102 103The size of pxe files and the number of labels is only limited by the amount 104of RAM available to U-Boot. Memory for labels is dynamically allocated as 105they're parsed, and memory for pxe files is statically allocated, and its 106location is given by the pxefile_addr_r environment variable. The pxe code is 107not aware of the size of the pxefile memory and will outgrow it if pxe files 108are too large. 109 110Supported global commands 111------------------------- 112Unrecognized commands are ignored. 113 114default <label> - the label named here is treated as the default and is 115 the first label 'pxe boot' attempts to boot. 116 117menu title <string> - sets a title for the menu of labels being displayed. 118 119menu include <path> - use tftp to retrieve the pxe file at <path>, which 120 is then immediately parsed as if the start of its 121 contents were the next line in the current file. nesting 122 of include up to 16 files deep is supported. 123 124prompt <flag> - if 1, always prompt the user to enter a label to boot 125 from. if 0, only prompt the user if timeout expires. 126 127timeout <num> - wait for user input for <num>/10 seconds before 128 auto-booting a node. 129 130label <name> - begin a label definition. labels continue until 131 a command not recognized as a label command is seen, 132 or EOF is reached. 133 134Supported label commands 135------------------------ 136labels end when a command not recognized as a label command is reached, or EOF. 137 138menu default - set this label as the default label to boot; this is 139 the same behavior as the global default command but 140 specified in a different way 141 142kernel <path> - if this label is chosen, use tftp to retrieve the kernel 143 (or FIT image) at <path>. it will be stored at the address 144 indicated in the kernel_addr_r environment variable, and 145 that address will be passed to bootm to boot this kernel. 146 For FIT image, The configuration specification can be 147 appended to the file name, with the format: 148 <path>#<conf>[#<extra-conf[#...]] 149 It will passed to bootm with that address. 150 (see: doc/uImage.FIT/command_syntax_extensions.txt) 151 It useful for overlay selection in pxe file 152 (see: doc/uImage.FIT/overlay-fdt-boot.txt) 153 154fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT 155 overlay(s) at <path>. it will be temporarily stored at the 156 address indicated in the fdtoverlay_addr_r environment variable, 157 and then applied in the load order to the fdt blob stored at the 158 address indicated in the fdt_addr_r environment variable. 159 160append <string> - use <string> as the kernel command line when booting this 161 label. 162 163initrd <path> - if this label is chosen, use tftp to retrieve the initrd 164 at <path>. it will be stored at the address indicated in 165 the initrd_addr_r environment variable, and that address 166 will be passed to bootm. 167 168fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob 169 at <path>. it will be stored at the address indicated in 170 the fdt_addr_r environment variable, and that address will 171 be passed to bootm. 172 173fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob 174 relative to <path>. If the fdtfile environment variable 175 is set, <path>/<fdtfile> is retrieved. Otherwise, the 176 filename is generated from the soc and board environment 177 variables, i.e. <path>/<soc>-<board>.dtb is retrieved. 178 If the fdt command is specified, fdtdir is ignored. 179 180localboot <flag> - Run the command defined by "localcmd" in the environment. 181 <flag> is ignored and is only here to match the syntax of 182 PXELINUX config files. 183 184Example 185------- 186Here's a couple of example files to show how this works. 187 188------------/tftpboot/pxelinux.cfg/menus/base.menu----------- 189menu title Linux selections 190 191# This is the default label 192label install 193 menu label Default Install Image 194 kernel kernels/install.bin 195 append console=ttyAMA0,38400 debug earlyprintk 196 initrd initrds/uzInitrdDebInstall 197 198# Just another label 199label linux-2.6.38 200 kernel kernels/linux-2.6.38.bin 201 append root=/dev/sdb1 202 203# The locally installed kernel 204label local 205 menu label Locally installed kernel 206 append root=/dev/sdb1 207 localboot 1 208------------------------------------------------------------- 209 210------------/tftpboot/pxelinux.cfg/default------------------- 211menu include pxelinux.cfg/menus/base.menu 212timeout 500 213 214default linux-2.6.38 215------------------------------------------------------------- 216 217When a pxe client retrieves and boots the default pxe file, 218'pxe boot' will wait for user input for 5 seconds before booting 219the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin 220to be downloaded, and boot with the command line "root=/dev/sdb1" 221 222Differences with PXELINUX 223========================= 224The biggest difference between U-Boot's pxe and PXELINUX is that since 225U-Boot's pxe support is written entirely in C, it can run on any platform 226with network support in U-Boot. Here are some other differences between 227PXELINUX and U-Boot's pxe support. 228 229- U-Boot's pxe does not support the PXELINUX DHCP option codes specified 230 in RFC 5071, but could be extended to do so. 231 232- when U-Boot's pxe fails to boot, it will return control to U-Boot, 233 allowing another command to run, other U-Boot command, instead of resetting 234 the machine like PXELINUX. 235 236- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it 237 only uses U-Boot. 238 239- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX 240 does, only a simple text based menu using the commands described in 241 this README. With PXELINUX, it's possible to have a graphical boot 242 menu, submenus, passwords, etc. U-Boot's pxe could be extended to support 243 a more robust menuing system like that of PXELINUX's. 244 245- U-Boot's pxe expects U-Boot uimg's as kernels. Anything that would work 246 with the 'bootm' command in U-Boot could work with the 'pxe boot' command. 247 248- U-Boot's pxe only recognizes a single file on the initrd command line. It 249 could be extended to support multiple. 250 251- in U-Boot's pxe, the localboot command doesn't necessarily cause a local 252 disk boot - it will do whatever is defined in the 'localcmd' env 253 variable. And since it doesn't support a full UNDI/PXE stack, the 254 type field is ignored. 255 256- the interactive prompt in U-Boot's pxe only allows you to choose a label 257 from the menu. If you want to boot something not listed, you can ctrl+c 258 out of 'pxe boot' and use existing U-Boot commands to accomplish it. 259