Re: [PATCH 11/16] bootm: implement plain and FIT bootm.image override

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi Ahmad,

On Thu, Mar 12, 2026 at 03:44:54PM +0100, Ahmad Fatoum wrote:
> Add support for overriding the boot image via bootm.image when using
> either plain files or FIT images. The override behavior depends on the
> file types involved:
> 
> - If the override is not a FIT image, it replaces only the OS loadable,
>   regardless of whether the original was a FIT image or not.
> 
> - If the override is a FIT image, it replaces the current OS, whether
>   it's a FIT or not.

What's the "current OS" here? Is it just the kernel or dtb/initrd as
well?

Sascha

> 
> This allows developers to use devboot scripts to redirect FIT image
> loading to alternate locations (e.g., network) while preserving the
> configuration selection from the original boot entry.
> 
> Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  commands/boot.c           |   2 +-
>  common/bootm-fit.c        |  11 +++-
>  common/bootm-overrides.c  | 119 +++++++++++++++++++++++++++++++++++++-
>  common/bootm.c            |   4 +-
>  include/bootm-fit.h       |   4 +-
>  include/bootm-overrides.h |   3 +
>  include/bootm.h           |   2 +
>  7 files changed, 134 insertions(+), 11 deletions(-)
> 
> diff --git a/commands/boot.c b/commands/boot.c
> index 555667ee098c..04bb9eb9186f 100644
> --- a/commands/boot.c
> +++ b/commands/boot.c
> @@ -44,7 +44,7 @@ static int boot_add_override(struct bootm_overrides *overrides, char *var)
>  	if (!strcmp(var, "bootm.image")) {
>  		if (isempty(val))
>  			return -EINVAL;
> -		return -ENOSYS;
> +		overrides->os_file = val;
>  	} else if (!strcmp(var, "bootm.oftree")) {
>  		overrides->oftree_file = val;
>  	} else if (!strcmp(var, "bootm.initrd")) {
> diff --git a/common/bootm-fit.c b/common/bootm-fit.c
> index 5b110ad2f19e..995bd7181223 100644
> --- a/common/bootm-fit.c
> +++ b/common/bootm-fit.c
> @@ -4,6 +4,7 @@
>  #include <image-fit.h>
>  #include <bootm-fit.h>
>  #include <memory.h>
> +#include <string.h>
>  #include <zero_page.h>
>  #include <filetype.h>
>  #include <fs.h>
> @@ -143,7 +144,7 @@ static enum filetype bootm_fit_update_os_header(struct image_data *data)
>  	return os_type;
>  }
>  
> -int bootm_open_fit(struct image_data *data)
> +int bootm_open_fit(struct image_data *data, bool override)
>  {
>  	struct fit_handle *fit;
>  	void *fit_config;
> @@ -164,8 +165,12 @@ int bootm_open_fit(struct image_data *data)
>  	}
>  
>  	loadable_from_fit_os(data, fit, fit_config);
> -	loadable_from_fit_initrd(data, fit, fit_config);
> -	loadable_from_fit_oftree(data, fit, fit_config);
> +	if (override)
> +		data->is_override.os = true;
> +	if (loadable_from_fit_initrd(data, fit, fit_config) && override)
> +		data->is_override.initrd = true;
> +	if (loadable_from_fit_oftree(data, fit, fit_config) && override)
> +		data->is_override.oftree = true;
>  	loadable_from_fit_tee(data, fit, fit_config);
>  
>  	data->kernel_type = bootm_fit_update_os_header(data);
> diff --git a/common/bootm-overrides.c b/common/bootm-overrides.c
> index 59ca90a58684..8c71ceb5f80d 100644
> --- a/common/bootm-overrides.c
> +++ b/common/bootm-overrides.c
> @@ -2,14 +2,118 @@
>  
>  #include <bootm.h>
>  #include <bootm-overrides.h>
> +#include <bootm-fit.h>
> +#include <libfile.h>
> +#include <linux/pagemap.h>
> +
> +/**
> + * bootm_apply_image_override - apply bootm.image override
> + * @data: image data context
> + * @override: override path (may include @config suffix for FIT)
> + *
> + * Applies a bootm.image override according to these rules:
> + * - If the override is not a FIT image, it replaces only data->os.
> + * - If the override is a FIT image, it is re-opened via bootm_open_fit()
> + *   using the default configuration or the @config suffix if given.
> + *
> + * Return: 0 on success, negative errno on failure
> + */
> +static int bootm_apply_image_override(struct image_data *data,
> +				      const char *override)
> +{
> +	char *override_file, *override_part;
> +	void *override_header = NULL;
> +	int ret;
> +
> +	ret = bootm_image_name_and_part(override, &override_file, &override_part);
> +	if (ret)
> +		return ret;
> +
> +	/* Read header to detect file type */
> +	ret = file_read_and_detect_boot_image_type(override_file, &override_header);
> +	if (ret < 0) {
> +		free(override_file);
> +		return ret;
> +	}
> +
> +	data->image_type = ret;
> +
> +	/*
> +	 * bootm_image_name_and_part() returns os_part pointing inside the
> +	 * os_file allocation, so we must NULLify os_part before freeing
> +	 * os_file to avoid a use-after-free.
> +	 */
> +	data->os_part = NULL;
> +	free(data->os_file);
> +	data->os_file = override_file;
> +	if (override_part)
> +		data->os_part = override_part;
> +
> +	/* Update the detected type for the handler */
> +	free(data->os_header);
> +	data->os_header = override_header;
> +
> +	switch (data->image_type) {
> +	case filetype_fit:
> +		/* Restore, so bootm_open_fit looks for them in the new FIT */
> +		data->os_address = data->os_address_hint;
> +		data->os_entry = data->os_entry_hint;
> +
> +		/* Re-open configuration and collect loadables */
> +		return bootm_open_fit(data, true);
> +	default:
> +		loadable_release(&data->os);
> +		data->os = loadable_from_file(override_file, LOADABLE_KERNEL);
> +		if (IS_ERR(data->os))
> +			return PTR_ERR(data->os);
> +
> +		data->kernel_type = data->image_type;
> +		data->is_override.os = true;
> +
> +		if (file_is_compressed_file(data->kernel_type))
> +			return bootm_open_os_compressed(data);
> +
> +		return 0;
> +	}
> +}
> +
> +static void report_active_override(const char *type_str, struct loadable *l)
> +{
> +	struct loadable *lc;
> +	char *buf = NULL;
> +
> +	if (!l) {
> +		pr_notice("[bootm override active] removed %s\n", type_str);
> +		return;
> +	}
> +
> +	buf = xrasprintf(buf, "[bootm override active] replacement %s: %s",
> +		      type_str, l->name);
> +
> +	list_for_each_entry(lc, &l->chained_loadables, list)
> +		buf = xrasprintf(buf, ", %s", lc->name);
> +
> +	pr_notice("%s\n", buf);
> +	free(buf);
> +}
> +
> +static void report_active_overrides(const struct image_data *data)
> +{
> +	if (data->is_override.os)
> +		report_active_override("OS", data->os);
> +	if (data->is_override.initrd)
> +		report_active_override("initrd", data->initrd);
> +	if (data->is_override.oftree)
> +		report_active_override("FDT", data->oftree);
> +}
>  
>  /**
>   * bootm_apply_overrides - apply overrides
>   * @data: image data context
>   * @overrides: overrides to apply
>   *
> - * Applies bootm.initrd and bootm.oftree overrides by translating
> - * them into file-based loadables.
> + * Applies bootm.image, bootm.initrd, and bootm.oftree overrides by translating
> + * them into file-based loadables or FIT image replacements.
>   *
>   * Context: Called during boot preparation
>   * Return: 0 on success, negative error code otherwise
> @@ -17,9 +121,17 @@
>  int bootm_apply_overrides(struct image_data *data,
>  			  const struct bootm_overrides *overrides)
>  {
> +	int ret;
> +
>  	if (bootm_signed_images_are_forced())
>  		return 0;
>  
> +	if (nonempty(overrides->os_file)) {
> +		ret = bootm_apply_image_override(data, overrides->os_file);
> +		if (ret)
> +			return ret;
> +	}
> +
>  	if (IS_ENABLED(CONFIG_BOOTM_INITRD) && overrides->initrd_file) {
>  		/* loadables_from_files() will set data->initrd on empty initrd_file */
>  		int ret = loadables_from_files(&data->initrd, overrides->initrd_file, ":",
> @@ -42,6 +154,7 @@ int bootm_apply_overrides(struct image_data *data,
>  		data->is_override.oftree = true;
>  	}
>  
> +	report_active_overrides(data);
> +
>  	return 0;
>  }
> -
> diff --git a/common/bootm.c b/common/bootm.c
> index ddc656fb34c8..ed79c20c0972 100644
> --- a/common/bootm.c
> +++ b/common/bootm.c
> @@ -400,7 +400,7 @@ static void bootm_print_info(struct image_data *data)
>  		printf("OS image not yet relocated\n");
>  }
>  
> -static int bootm_image_name_and_part(const char *name, char **filename, char **part)
> +int bootm_image_name_and_part(const char *name, char **filename, char **part)
>  {
>  	char *at, *ret;
>  
> @@ -570,7 +570,7 @@ struct image_data *bootm_boot_prep(const struct bootm_data *bootm_data)
>  
>  	switch (data->image_type) {
>  	case filetype_fit:
> -		ret = bootm_open_fit(data);
> +		ret = bootm_open_fit(data, false);
>  		break;
>  	case filetype_uimage:
>  		ret = bootm_open_uimage(data);
> diff --git a/include/bootm-fit.h b/include/bootm-fit.h
> index 05f4f5acfe9a..972d9e4fac8e 100644
> --- a/include/bootm-fit.h
> +++ b/include/bootm-fit.h
> @@ -10,11 +10,11 @@ struct image_data;
>  
>  #ifdef CONFIG_BOOTM_FITIMAGE
>  
> -int bootm_open_fit(struct image_data *data);
> +int bootm_open_fit(struct image_data *data, bool override);
>  
>  #else
>  
> -static inline int bootm_open_fit(struct image_data *data)
> +static inline int bootm_open_fit(struct image_data *data, bool override)
>  {
>  	return -ENOSYS;
>  }
> diff --git a/include/bootm-overrides.h b/include/bootm-overrides.h
> index a52a498b97a2..9b133928a923 100644
> --- a/include/bootm-overrides.h
> +++ b/include/bootm-overrides.h
> @@ -3,6 +3,7 @@
>  #define __BOOTM_OVERRIDES_H
>  
>  struct bootm_overrides {
> +	const char *os_file;
>  	const char *oftree_file;
>  	const char *initrd_file;
>  };
> @@ -13,6 +14,8 @@ struct image_data;
>  static inline void bootm_merge_overrides(struct bootm_overrides *dst,
>  					 const struct bootm_overrides *src)
>  {
> +	if (src->os_file)
> +		dst->os_file = src->os_file;
>  	if (src->oftree_file)
>  		dst->oftree_file = src->oftree_file;
>  	if (src->initrd_file)
> diff --git a/include/bootm.h b/include/bootm.h
> index 570ac4d289f2..85199fc702b4 100644
> --- a/include/bootm.h
> +++ b/include/bootm.h
> @@ -53,6 +53,8 @@ struct bootm_data {
>  	unsigned long os_entry;
>  };
>  
> +int bootm_image_name_and_part(const char *name, char **filename, char **part);
> +
>  int bootm_boot(const struct bootm_data *data);
>  
>  struct image_data *bootm_boot_prep(const struct bootm_data *bootm_data);
> -- 
> 2.47.3
> 
> 
> 

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