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Diffstat (limited to 'Documentation/admin-guide/bootconfig.rst')
| -rw-r--r-- | Documentation/admin-guide/bootconfig.rst | 34 |
1 files changed, 31 insertions, 3 deletions
diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst index b342a6796392..cf2edcd09183 100644 --- a/Documentation/admin-guide/bootconfig.rst +++ b/Documentation/admin-guide/bootconfig.rst @@ -62,6 +62,30 @@ Or more shorter, written as following:: In both styles, same key words are automatically merged when parsing it at boot time. So you can append similar trees or key-values. +Same-key Values +--------------- + +It is prohibited that two or more values or arrays share a same-key. +For example,:: + + foo = bar, baz + foo = qux # !ERROR! we can not re-define same key + +If you want to append the value to existing key as an array member, +you can use ``+=`` operator. For example:: + + foo = bar, baz + foo += qux + +In this case, the key ``foo`` has ``bar``, ``baz`` and ``qux``. + +However, a sub-key and a value can not co-exist under a parent key. +For example, following config is NOT allowed.:: + + foo = value1 + foo.bar = value2 # !ERROR! subkey "bar" and value "value1" can NOT co-exist + + Comments -------- @@ -102,9 +126,13 @@ Boot Kernel With a Boot Config ============================== Since the boot configuration file is loaded with initrd, it will be added -to the end of the initrd (initramfs) image file. The Linux kernel decodes -the last part of the initrd image in memory to get the boot configuration -data. +to the end of the initrd (initramfs) image file with size, checksum and +12-byte magic word as below. + +[initrd][bootconfig][size(u32)][checksum(u32)][#BOOTCONFIG\n] + +The Linux kernel decodes the last part of the initrd image in memory to +get the boot configuration data. Because of this "piggyback" method, there is no need to change or update the boot loader and the kernel image itself. |