From 85c46b78da58398be1c5166f55063c0512decd39 Mon Sep 17 00:00:00 2001 From: Masami Hiramatsu Date: Thu, 20 Feb 2020 21:18:42 +0900 Subject: bootconfig: Add bootconfig magic word for indicating bootconfig explicitly Add bootconfig magic word to the end of bootconfig on initrd image for indicating explicitly the bootconfig is there. Also tools/bootconfig treats wrong size or wrong checksum or parse error as an error, because if there is a bootconfig magic word, there must be a bootconfig. The bootconfig magic word is "#BOOTCONFIG\n", 12 bytes word. Thus the block image of the initrd file with bootconfig is as follows. [Initrd][bootconfig][size][csum][#BOOTCONFIG\n] Link: http://lkml.kernel.org/r/158220112263.26565.3944814205960612841.stgit@devnote2 Suggested-by: Steven Rostedt Signed-off-by: Masami Hiramatsu Signed-off-by: Steven Rostedt (VMware) --- Documentation/admin-guide/bootconfig.rst | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'Documentation') diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst index b342a6796392..5e7609936507 100644 --- a/Documentation/admin-guide/bootconfig.rst +++ b/Documentation/admin-guide/bootconfig.rst @@ -102,9 +102,13 @@ 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. -- cgit v1.2.3