[RFC] kexec: Add bootconfig support to get_command_line

[Breno Leitao]

On Mon, Aug 11, 2025 at 04:37:36PM +0100, Usama Arif wrote:
> If the kernel is enabled with CONFIG_BOOT_CONFIG_FORCE, it will
> always append the bootconfig at the start of the kernel commandline.
> If reuse-cmdline option is used in kexec, the bootconfig will be
> repeatedly appended at the start of the commandline on every kexec.
> As there is a limit on the size of kernel commandline that can be
> used, --reuse-cmdline option will break kexec depending on the
> size of bootconfig on repeated kexec.
> 
> Bootconfig is embedded in the kernel, so it should not be considered
> when reusing kernel command line.
> Modify get_command_line() to first attempt reading kernel parameters
> from /proc/bootconfig before falling back to /proc/cmdline. This allows
> kexec to use the original boot parameters without bootconfig which
> is embedded in the kernel.
> 
> The function will fallback to /proc/cmdline behavior when:
> 
> - /proc/bootconfig doesn't exist
> - /proc/bootconfig is empty
> - /proc/bootconfig doesn't contain the expected marker format
> - The extracted parameter line is empty
> 
> Signed-off-by: Usama Arif <usamaarif642 at gmail.com>

Reviewed-by: Breno Leitao <leitao at debian.org>