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 For FIT image, The configuration specification can be 144 appended to the file name, with the format: 145 <path>#<conf>[#<extra-conf[#...]] 146 It will passed to bootm with that address. 147 (see: doc/uImage.FIT/command_syntax_extensions.txt) 148 It useful for overlay selection in pxe file 149 (see: doc/uImage.FIT/overlay-fdt-boot.txt) 150 151append <string> - use <string> as the kernel command line when booting this 152 label. 153 154initrd <path> - if this label is chosen, use tftp to retrieve the initrd 155 at <path>. it will be stored at the address indicated in 156 the initrd_addr_r environment variable, and that address 157 will be passed to bootm. 158 159fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob 160 at <path>. it will be stored at the address indicated in 161 the fdt_addr_r environment variable, and that address will 162 be passed to bootm. 163 164fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob 165 relative to <path>. If the fdtfile environment variable 166 is set, <path>/<fdtfile> is retrieved. Otherwise, the 167 filename is generated from the soc and board environment 168 variables, i.e. <path>/<soc>-<board>.dtb is retrieved. 169 If the fdt command is specified, fdtdir is ignored. 170 171localboot <flag> - Run the command defined by "localcmd" in the environment. 172 <flag> is ignored and is only here to match the syntax of 173 PXELINUX config files. 174 175Example 176------- 177Here's a couple of example files to show how this works. 178 179------------/tftpboot/pxelinux.cfg/menus/base.menu----------- 180menu title Linux selections 181 182# This is the default label 183label install 184 menu label Default Install Image 185 kernel kernels/install.bin 186 append console=ttyAMA0,38400 debug earlyprintk 187 initrd initrds/uzInitrdDebInstall 188 189# Just another label 190label linux-2.6.38 191 kernel kernels/linux-2.6.38.bin 192 append root=/dev/sdb1 193 194# The locally installed kernel 195label local 196 menu label Locally installed kernel 197 append root=/dev/sdb1 198 localboot 1 199------------------------------------------------------------- 200 201------------/tftpboot/pxelinux.cfg/default------------------- 202menu include pxelinux.cfg/menus/base.menu 203timeout 500 204 205default linux-2.6.38 206------------------------------------------------------------- 207 208When a pxe client retrieves and boots the default pxe file, 209'pxe boot' will wait for user input for 5 seconds before booting 210the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin 211to be downloaded, and boot with the command line "root=/dev/sdb1" 212 213Differences with PXELINUX 214========================= 215The biggest difference between U-Boot's pxe and PXELINUX is that since 216U-Boot's pxe support is written entirely in C, it can run on any platform 217with network support in U-Boot. Here are some other differences between 218PXELINUX and U-Boot's pxe support. 219 220- U-Boot's pxe does not support the PXELINUX DHCP option codes specified 221 in RFC 5071, but could be extended to do so. 222 223- when U-Boot's pxe fails to boot, it will return control to U-Boot, 224 allowing another command to run, other U-Boot command, instead of resetting 225 the machine like PXELINUX. 226 227- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it 228 only uses U-Boot. 229 230- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX 231 does, only a simple text based menu using the commands described in 232 this README. With PXELINUX, it's possible to have a graphical boot 233 menu, submenus, passwords, etc. U-Boot's pxe could be extended to support 234 a more robust menuing system like that of PXELINUX's. 235 236- U-Boot's pxe expects U-Boot uimg's as kernels. Anything that would work 237 with the 'bootm' command in U-Boot could work with the 'pxe boot' command. 238 239- U-Boot's pxe only recognizes a single file on the initrd command line. It 240 could be extended to support multiple. 241 242- in U-Boot's pxe, the localboot command doesn't necessarily cause a local 243 disk boot - it will do whatever is defined in the 'localcmd' env 244 variable. And since it doesn't support a full UNDI/PXE stack, the 245 type field is ignored. 246 247- the interactive prompt in U-Boot's pxe only allows you to choose a label 248 from the menu. If you want to boot something not listed, you can ctrl+c 249 out of 'pxe boot' and use existing U-Boot commands to accomplish it. 250