Re: [PATCH v3 06/10] of: overlay: add FIT overlay support

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

On Wed, Jul 03, 2024 at 06:58:34PM +0200, Marco Felsch wrote:
> This adds the support to load devicetree overlays from an FIT image.
> There are quite a few options to handle FIT overlays since the FIT
> overlay spec is not very strict.
> 
> This patch implement the most configurable case where each overlay does
> have it's own config node (including the optional signature).
> 
> - The "name" filter check is performed on the config-node name (the node
>   under the configurations) and not the FIT overlay image name (the node
>   name under the images node).
> - The "content" filter check does not differ from the file based overlay
>   handling.
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
>  drivers/of/overlay.c | 131 ++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 124 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 5617f322ddca..a980e7aa5e02 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -8,10 +8,13 @@
>   */
>  #define pr_fmt(fmt) "of_overlay: " fmt
>  
> +#include <bootm.h>
>  #include <common.h>
>  #include <of.h>
>  #include <errno.h>
> +#include <filetype.h>
>  #include <globalvar.h>
> +#include <image-fit.h>
>  #include <magicvar.h>
>  #include <string.h>
>  #include <libfile.h>
> @@ -470,9 +473,123 @@ static int of_overlay_global_fixup_dir(struct device_node *root, const char *ovl
>  	return ret;
>  }
>  
> +static int of_overlay_apply_fit(struct device_node *root, struct fit_handle *fit,
> +				struct device_node *config)
> +{
> +	const char *name = config->name;
> +	struct device_node *overlay;
> +	unsigned long ovl_sz;
> +	const void *ovl;
> +	int ret;
> +
> +	if (!of_overlay_matches_filter(name, NULL))
> +		return 0;
> +
> +	ret = fit_open_image(fit, config, "fdt", &ovl, &ovl_sz);
> +	if (ret)
> +		return ret;
> +
> +	overlay = of_unflatten_dtb(ovl, ovl_sz);
> +
> +	if (!of_overlay_matches_filter(NULL, overlay)) {
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	ret = of_overlay_apply_tree(root, overlay);
> +	if (ret == -ENODEV)
> +		pr_debug("Not applied %s (not compatible)\n", name);
> +	else if (ret)
> +		pr_err("Cannot apply %s: %s\n", name, strerror(-ret));
> +	else
> +		pr_info("Applied %s\n", name);
> +
> +out:
> +	of_delete_node(overlay);
> +
> +	return ret;
> +}
> +
> +static bool of_overlay_valid_config(struct fit_handle *fit,
> +				    struct device_node *config)
> +{
> +	/*
> +	 * Either kernel or firmware is marked as mandatory by U-Boot
> +	 * (doc/usage/fit/source_file_format.rst) except for overlays
> +	 * (doc/usage/fit/overlay-fdt-boot.rst). Therefore we need to ensure
> +	 * that only "fdt" config nodes are recognized as overlay config node.
> +	 */
> +	if (!fit_has_image(fit, config, "fdt") ||
> +	    fit_has_image(fit, config, "kernel") ||
> +	    fit_has_image(fit, config, "firmware"))
> +		return false;
> +
> +	return true;
> +}
> +
> +static int of_overlay_global_fixup_fit(struct device_node *root,
> +				       const char *fit_path, loff_t fit_size)
> +{
> +	enum bootm_verify verify = bootm_get_verify_mode();
> +	struct device_node *conf_node;
> +	struct fit_handle *fit;
> +	int ret;
> +
> +	if (!IS_ENABLED(CONFIG_FITIMAGE))
> +		return 0;

The user has explicitly passed a FIT image, but we don't have FIT
support compiled in. Shouldn't this be an error?

> +
> +	fit = fit_open(fit_path, 0, verify, fit_size);
> +	if (IS_ERR(fit)) {
> +		pr_err("Loading FIT image %s failed with: %pe\n", fit_path, fit);
> +		return PTR_ERR(fit);
> +	}
> +
> +	for_each_child_of_node(fit->configurations, conf_node) {
> +		if (!of_overlay_valid_config(fit, conf_node))
> +			continue;
> +
> +		ret = fit_config_verify_signature(fit, conf_node);
> +		if (ret)
> +			goto out;
> +
> +		ret = of_overlay_apply_fit(root, fit, conf_node);
> +		if (ret)
> +			goto out;
> +	}
> +
> +out:
> +	fit_close(fit);
> +	return ret;
> +}
> +
>  static int of_overlay_global_fixup(struct device_node *root, void *data)
>  {
> -	return of_overlay_global_fixup_dir(root, of_overlay_path);
> +	enum filetype type;
> +	struct stat s;
> +	int ret;
> +
> +	if (isempty(of_overlay_path))
> +		return 0;
> +
> +	if (stat(of_overlay_path, &s)) {
> +		pr_err("Failed to detect file status\n");

Maybe something like:

	pr_err("Cannot stat global.of.overlay.path (%s): %pe\n", of_overlay_path, ERR_PTR(ret));

To give the user a better clue what to do about this error?

> +		return -errno;
> +	}
> +
> +	if (S_ISDIR(s.st_mode))
> +		return of_overlay_global_fixup_dir(root, of_overlay_path);
> +
> +	ret = file_name_detect_type(of_overlay_path, &type);
> +	if (ret)
> +		return ret;
> +
> +	if (type == filetype_oftree)
> +		return of_overlay_global_fixup_fit(root, of_overlay_path,
> +						   s.st_size);
> +
> +	pr_err("No suitable overlay provider found!\n");

What other file types are you anticipating here? I would rather assume a
"... is not a FIT image" message to give the user a clue what is
expected here.

I think you could also just drop the filetype detection here and just
call of_overlay_global_fixup_fit() unconditionally. The resulting
"Loading FIT image %s failed with: %pe\n" message when a non FIT image
is to be opened should be enough information for the user.

Note that it's a bit unfortunate that both a FIT image and a dtbo file
are detected as device tree files. With the prvious naming
"global.of.overlay.dir" it was clear that a directory was expected here.
The "global.of.overlay.path" naming might confuse the user into thinking
that a path to a dtbo file could be passed here which would then be
opened as a FIT image. Would be nice to give a meaningful error message
when a user falls into this trap.

Sascha

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