Lines Matching +full:boot +full:- +full:loader
1 .. SPDX-License-Identifier: GPL-2.0
6 Boot Configuration
14 The boot configuration expands the current kernel command line to support
15 additional key-value data when booting the kernel in an efficient way.
16 This allows administrators to pass a structured-Key config file.
21 The boot config syntax is a simple structured key-value. Each key consists
22 of dot-connected-words, and key and value are connected by ``=``. The value
23 has to be terminated by semi-colon (``;``) or newline (``\n``).
30 Each key word must contain only alphabets, numbers, dash (``-``) or underscore
32 for delimiters such as semi-colon (``;``), new-line (``\n``), comma (``,``),
35 If you want to use those delimiters in a value, you can use either double-
36 quotes (``"VALUE"``) or single-quotes (``'VALUE'``) to quote it. Note that
42 Key-Value Syntax
43 ----------------
45 The boot config file syntax allows user to merge partially same word keys
63 at boot time. So you can append similar trees or key-values.
65 Same-key Values
66 ---------------
68 It is prohibited that two or more values or arrays share a same-key.
72 foo = qux # !ERROR! we can not re-define same key
92 Moreover, sub-keys and a value can coexist under a parent key.
123 --------
125 The config syntax accepts shell-script style comments. The comments starting
151 /proc/bootconfig is a user-space interface of the boot config.
152 Unlike /proc/cmdline, this file shows the key-value style list.
153 Each key-value pair is shown in each line with following style::
158 Boot Kernel With a Boot Config
161 There are two options to boot the kernel with bootconfig: attaching the
164 Attaching a Boot Config to Initrd
165 ---------------------------------
167 Since the boot configuration file is loaded with initrd by default,
169 padding, size, checksum and 12-byte magic word as below.
175 When the boot configuration is added to the initrd image, the total
181 get the boot configuration data.
183 update the boot loader and the kernel image itself as long as the boot
184 loader passes the correct initrd file size. If by any chance, the boot
185 loader passes a longer size, the kernel fails to find the bootconfig data.
191 # make -C tools/bootconfig
193 To add your boot config file to initrd image, run bootconfig as below
196 # tools/bootconfig/bootconfig -a your-config /boot/initrd.img-X.Y.Z
198 To remove the config from the image, you can use -d option as below::
200 # tools/bootconfig/bootconfig -d /boot/initrd.img-X.Y.Z
207 Embedding a Boot Config into Kernel
208 -----------------------------------
229 Kernel parameters via Boot Config
232 In addition to the kernel command line, the boot config can be used for
233 passing the kernel parameters. All the key-value pairs under ``kernel``
234 key will be passed to kernel cmdline directly. Moreover, the key-value
236 The parameters are concatenated with user-given kernel cmdline string
241 [bootconfig params][cmdline params] -- [bootconfig init params][cmdline init params]
246 root = 01234567-89ab-cdef-0123-456789abcd
254 root="01234567-89ab-cdef-0123-456789abcd" -- splash
258 ro bootconfig -- quiet
262 root="01234567-89ab-cdef-0123-456789abcd" ro bootconfig -- splash quiet
268 Currently the maximum config size size is 32KB and the total key-words (not
269 key-value entries) must be under 1024 nodes.
271 more than 2 nodes (a key-word and a value). So theoretically, it will be
272 up to 512 key-value pairs. If keys contains 3 words in average, it can
273 contain 256 key-value pairs. In most cases, the number of config items
278 Anyway, since bootconfig command verifies it when appending a boot config
279 to initrd image, user can notice it before boot.
285 User can query or loop on key-value pairs, also it is possible to find
286 a root (prefix) key node and find key-values under that node.
289 using xbc_find_value(). If you want to know what keys exist in the boot
290 config, you can use xbc_for_each_key_value() to iterate key-value pairs.
311 xbc_node_for_each_array_value(root, "array-option", value, anode) {
316 "key.prefix.array-option".
319 read-only. All data and keys must be copied if you need to modify it.
325 .. kernel-doc:: include/linux/bootconfig.h
326 .. kernel-doc:: lib/bootconfig.c