Documentation/admin-guide/bootconfig.rst

15 additional key-value data when booting the kernel in an efficient way.
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
30 Each key word must contain only alphabets, numbers, dash (``-``) or underscore
39 There can be a key which doesn't have value or has an empty value. Those keys
40 are used for checking if the key exists or not (like a boolean).
62 In both styles, same key words are automatically merged when parsing it
63 at boot time. So you can append similar trees or key-values.
65 Same-key Values
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
80 then, the ``qux`` is assigned to ``foo`` key. This is useful for
84 If you want to append the value to existing key as an array member,
90 In this case, the key ``foo`` has ``bar``, ``baz`` and ``qux``.
92 Moreover, sub-keys and a value can coexist under a parent key.
100 structured key, you have to define it outside of the brace. For example::
110 Also, the order of the value node under a key is fixed. If there
112 of the key. Thus if user specifies subkeys first, e.g.::
144  key = 1 # comment
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::
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
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
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.
288 If you have a key string, you can query the value directly with the key
290 config, you can use xbc_for_each_key_value() to iterate key-value pairs.
295  xbc_find_value("key.word", &vnode);
308  root = xbc_find_node("key.prefix");
315 This accesses a value of "key.prefix.option" and an array of
316 "key.prefix.array-option".