[PATCH 4/4] bootm: introduce bootm.root_arg variable

[Ahmad Fatoum]

On 11/26/25 7:42 AM, Fabian Pflug wrote:
> The bootm.root_arg variable will be responsible for the root= part of
> the kernel commandline if bootm.appendroot is set and a root device has
> been selected.
> root_arg allows to replace the root=/dev/... with verity=/dev/..., which
> is useful in a verified boot context, where you pass the root file
> system to the initramfs, but do not want the kernel to be able to parse
> and mount the rootfs. With renaming the root= to something different,
> you make sure, that the kernel does not mount the rootfs.
> 
> Signed-off-by: Fabian Pflug <f.pflug at pengutronix.de>
> ---
>  common/bootm.c  | 8 ++++++--
>  include/bootm.h | 1 +
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/common/bootm.c b/common/bootm.c
> index 5d7dc00e3e..a1aba06f0e 100644
> --- a/common/bootm.c
> +++ b/common/bootm.c
> @@ -69,6 +69,7 @@ void bootm_data_init_defaults(struct bootm_data *data)
>  		data->initrd_file = getenv_nonempty("global.bootm.initrd");
>  	}
>  	data->root_dev = getenv_nonempty("global.bootm.root_dev");
> +	data->root_arg = getenv_nonempty("global.bootm.root_arg");
>  	data->verify = bootm_get_verify_mode();
>  	data->appendroot = bootm_appendroot;
>  	data->provide_machine_id = bootm_provide_machine_id;
> @@ -88,6 +89,7 @@ void bootm_data_restore_defaults(const struct bootm_data *data)
>  		globalvar_set("bootm.initrd", data->initrd_file);
>  	}
>  	globalvar_set("bootm.root_dev", data->root_dev);
> +	globalvar_set("bootm.root_arg", data->root_arg);
>  	bootm_set_verify_mode(data->verify);
>  	bootm_appendroot = data->appendroot;
>  	bootm_provide_machine_id = data->provide_machine_id;
> @@ -868,10 +870,10 @@ int bootm_boot(struct bootm_data *bootm_data)
>  		} else {
>  			char *rootarg;
>  			if(rootopts) {
> -				rootarg = xasprintf("root=%s %s", root, rootopts);
> +				rootarg = xasprintf("%s=%s %s", bootm_data->root_arg, root, rootopts);
>  				free(rootopts);
>  			} else {
> -				rootarg = xasprintf("root=%s", root);
> +				rootarg = xasprintf("%s=%s", bootm_data->root_arg, root);
>  			}
>  			free(root);
>  			pr_info("Adding \"%s\" to Kernel commandline\n", rootarg);
> @@ -1116,6 +1118,7 @@ static int bootm_init(void)
>  	globalvar_add_simple("bootm.image.loadaddr", NULL);
>  	globalvar_add_simple("bootm.oftree", NULL);
>  	globalvar_add_simple("bootm.root_dev", NULL);
> +	globalvar_add_simple("bootm.root_arg", "root");
>  	globalvar_add_simple("bootm.tee", NULL);
>  	globalvar_add_simple_bool("bootm.appendroot", &bootm_appendroot);
>  	globalvar_add_simple_bool("bootm.earlycon", &bootm_earlycon);
> @@ -1173,5 +1176,6 @@ BAREBOX_MAGICVAR(global.bootm.verbose, "bootm default verbosity level (0=quiet)"
>  BAREBOX_MAGICVAR(global.bootm.earlycon, "Add earlycon option to Kernel for early log output");
>  BAREBOX_MAGICVAR(global.bootm.appendroot, "Add root= option to Kernel to mount rootfs from the device the Kernel comes from (default, device can be overridden via global.bootm.root_dev)");
>  BAREBOX_MAGICVAR(global.bootm.root_dev, "bootm default root device (overrides default device in global.bootm.appendroot)");
> +BAREBOX_MAGICVAR(global.bootm.root_arg, "bootm default name arg for the root partition (normally 'root' for root=/dev/...)");

s/default name arg/default parameter name/

?

>  BAREBOX_MAGICVAR(global.bootm.provide_machine_id, "If true, append systemd.machine_id=$global.machine_id to Kernel command line");
>  BAREBOX_MAGICVAR(global.bootm.provide_hostname, "If true, append systemd.hostname=$global.hostname to Kernel command line");
> diff --git a/include/bootm.h b/include/bootm.h
> index b35deb25bf..43f4258885 100644
> --- a/include/bootm.h
> +++ b/include/bootm.h
> @@ -19,6 +19,7 @@ struct bootm_data {
>  	const char *oftree_file;
>  	const char *tee_file;
>  	const char *root_dev;
> +	const char *root_arg;
>  	int verbose;
>  	enum bootm_verify verify;
>  	bool force;

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