Re: [PATCH 2/5] fdtput: Follow an alias when creating nodes with -p

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Oct 27, 2026 at 06:01:16AM -0600, Simon Glass wrote:
> A node path can start with an alias, such as serial0/sub, but -p does
> not allow for this. It looks up each part of the path from the root, so
> it creates a top-level node named after the alias:
> 
>    $ fdtput -cp test.dtb serial0/sub
> 
> This creates /serial0/sub instead of adding 'sub' to the node which
> serial0 points to, and reports success. When writing a property, the
> stray node is left behind if the alias is the whole path, and fdtput
> fails if the path continues beyond the alias.
> 
> When the path starts with an alias, create any missing nodes below the
> node which the alias points to. Keep the existing behaviour for other
> paths which do not start with '/', which are created from the root.
> 
> Fixes: f807af192828 ("fdtput: Add -p option to create subnodes along entire path")
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
> 
>  fdtput.c           | 18 ++++++++++++++++--
>  tests/run_tests.sh |  7 +++++++
>  2 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/fdtput.c b/fdtput.c
> index c139de1..4094015 100644
> --- a/fdtput.c
> +++ b/fdtput.c
> @@ -201,8 +201,9 @@ static int store_key_value(char **blob, const char *node_name,
>  /**
>   * Create paths as needed for all components of a path
>   *
> - * Any components of the path that do not exist are created. Errors are
> - * reported.
> + * Any components of the path that do not exist are created. If the path
> + * starts with an alias, they are created below the node which the alias
> + * points to. Otherwise the path starts at the root. Errors are reported.
>   *
>   * @param blob		FDT blob to write into
>   * @param in_path	Path to process
> @@ -214,6 +215,19 @@ static int create_paths(char **blob, const char *in_path)
>  	const char *sep;
>  	int node, offset = 0;
>  
> +	/* a path which starts with an alias is created below its node */
> +	sep = strchr(path, '/');
> +	if (!sep)
> +		sep = path + strlen(path);
> +	if (sep > path && fdt_get_alias_namelen(*blob, path, sep - path)) {
> +		offset = fdt_path_offset_namelen(*blob, path, sep - path);
> +		if (offset < 0) {
> +			report_error(path, sep - path, offset);
> +			return -1;
> +		}
> +		path = sep;
> +	}
> +

The previous behaviour was certainly buggy, but I don't think this fix
is quite correct.  If 'foo' is *not* an existing alias, then
	fdtput -cp test.dtb foo/bar/baz
Will still create /foo/bar/baz, which is not how dt paths generally
work.

Instead, we should look for an alias if and only if there's no leading
'/'.  If there's no leading '/' but the first segment is not a valid
alias, then we should error out.

>  	/* skip leading '/' */
>  	while (*path == '/')
>  		path++;
> diff --git a/tests/run_tests.sh b/tests/run_tests.sh
> index 842b543..77f0a81 100755
> --- a/tests/run_tests.sh
> +++ b/tests/run_tests.sh
> @@ -970,6 +970,13 @@ fdtput_tests () {
>  	"-ts" "fine wine"
>      run_wrap_test $DTPUT $dtb -p /you/are/drunk/sir/winston slurp -ts twice
>  
> +    # Automatic node creation below an alias
> +    run_wrap_test $DTPUT $dtb -p /aliases second -ts /blackadder/the-second
> +    run_wrap_test $DTPUT $dtb -cp second/carrot
> +    run_fdtput_test "orange" $dtb second/carrot colour -ts "orange"
> +    run_fdtget_test "orange" $dtb /blackadder/the-second/carrot colour
> +    run_wrap_error_test $DTGET $dtb -l /second
> +
>      # Test expansion of the blob when insufficient room for a new node
>      run_wrap_test $DTPUT $dtb -cp "$(cat $text $text)/longish"
>  
> -- 
> 2.43.0
> 
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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