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| -rw-r--r-- | Documentation/admin-guide/bootconfig.rst | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst index 6a79f2e59396..a1860fc0ca88 100644 --- a/Documentation/admin-guide/bootconfig.rst +++ b/Documentation/admin-guide/bootconfig.rst @@ -178,7 +178,7 @@ update the boot loader and the kernel image itself as long as the boot loader passes the correct initrd file size. If by any chance, the boot loader passes a longer size, the kernel fails to find the bootconfig data. -To do this operation, Linux kernel provides "bootconfig" command under +To do this operation, Linux kernel provides ``bootconfig`` command under tools/bootconfig, which allows admin to apply or delete the config file to/from initrd image. You can build it by the following command:: @@ -196,6 +196,43 @@ To remove the config from the image, you can use -d option as below:: Then add "bootconfig" on the normal kernel command line to tell the kernel to look for the bootconfig at the end of the initrd file. + +Kernel parameters via Boot Config +================================= + +In addition to the kernel command line, the boot config can be used for +passing the kernel parameters. All the key-value pairs under ``kernel`` +key will be passed to kernel cmdline directly. Moreover, the key-value +pairs under ``init`` will be passed to init process via the cmdline. +The parameters are concatinated with user-given kernel cmdline string +as the following order, so that the command line parameter can override +bootconfig parameters (this depends on how the subsystem handles parameters +but in general, earlier parameter will be overwritten by later one.):: + + [bootconfig params][cmdline params] -- [bootconfig init params][cmdline init params] + +Here is an example of the bootconfig file for kernel/init parameters.:: + + kernel { + root = 01234567-89ab-cdef-0123-456789abcd + } + init { + splash + } + +This will be copied into the kernel cmdline string as the following:: + + root="01234567-89ab-cdef-0123-456789abcd" -- splash + +If user gives some other command line like,:: + + ro bootconfig -- quiet + +The final kernel cmdline will be the following:: + + root="01234567-89ab-cdef-0123-456789abcd" ro bootconfig -- splash quiet + + Config File Limitation ====================== |