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1 .. SPDX-License-Identifier: GPL-2.0
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 ----------------
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.
99 Note, since there is no syntax to put a raw value directly under a
110 Also, the order of the value node under a key is fixed. If there
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::
165 ---------------------------------
169 padding, size, checksum and 12-byte magic word as below.
187 To do this operation, Linux kernel provides ``bootconfig`` command under
191 # make -C tools/bootconfig
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
208 -----------------------------------
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
235 pairs under ``init`` will be passed to init process via the cmdline.
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
274 will be under 100 entries and smaller than 8KB, so it would be enough.
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.
290 config, you can use xbc_for_each_key_value() to iterate key-value pairs.
303 keys under the prefix node with xbc_node_for_each_key_value().
305 But the most typical usage is to get the named value under prefix
306 or get the named array under prefix as below::
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