Re: [RFC PATCH v2 03/74] fdtdump: Introduce get_structured_tag_data()

[David Gibson]

On Wed, Aug 26, 2026 at 11:48:32AM +0200, Herve Codina wrote:
> With structured tag, data len can be encoded in the tag itself (no data,
> 1 cell data, 2 cells) or with a dedicated cell (varlen) added between
> the tag and the data.
> 
> In multiple places, getting the data related to the tag will be needed.
> 
> In order to avoid code duplication, introduce get_structured_tag_data()
> which purpose is to get the tag data part and its length based on the
> tag value.
> 
> Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>

This might as well be folded into the initial implementation of
structured tags in the earlier series.

> ---
>  fdtdump.c | 50 ++++++++++++++++++++++++++++++--------------------
>  1 file changed, 30 insertions(+), 20 deletions(-)
> 
> diff --git a/fdtdump.c b/fdtdump.c
> index 20854752..f26d3a89 100644
> --- a/fdtdump.c
> +++ b/fdtdump.c
> @@ -44,6 +44,33 @@ static const char *tagname(uint32_t tag)
>  #define dumpf(fmt, args...) \
>  	do { if (debug) printf("// " fmt, ## args); } while (0)
>  
> +static const char *get_structured_tag_data(uint32_t tag, const char *blob,
> +					   const char **data, int *data_size)
> +{
> +	int sz = 0;
> +
> +	switch (tag & FDT_TAG_DATA_MASK) {
> +	case FDT_TAG_DATA_NONE:
> +		break;
> +	case FDT_TAG_DATA_1CELL:
> +		sz = FDT_CELLSIZE;
> +		break;
> +	case FDT_TAG_DATA_2CELLS:
> +		sz = 2 * FDT_CELLSIZE;
> +		break;
> +	case FDT_TAG_DATA_VARLEN:
> +		/* Get the length */
> +		sz = fdt32_to_cpu(GET_CELL(blob));
> +		break;
> +	}
> +
> +	*data_size = sz;
> +	*data = sz ? blob : NULL;
> +
> +	/* Skip the data bytes */
> +	return PALIGN(blob + sz, 4);
> +}
> +
>  static void dump_blob(void *blob, bool debug, int dump_unknown)
>  {
>  	uintptr_t blob_off = (uintptr_t)blob;
> @@ -58,7 +85,7 @@ static void dump_blob(void *blob, bool debug, int dump_unknown)
>  	uint32_t version = fdt32_to_cpu(bph->version);
>  	uint32_t totalsize = fdt32_to_cpu(bph->totalsize);
>  	uint32_t tag;
> -	const char *p, *s, *t;
> +	const char *p, *d, *s, *t;
>  	int depth, sz, shift;
>  	int i;
>  	uint64_t addr, size;
> @@ -153,21 +180,7 @@ static void dump_blob(void *blob, bool debug, int dump_unknown)
>  		}
>  
>  		if ((tag & FDT_TAG_STRUCTURED) && (tag & FDT_TAG_SKIP_SAFE)) {
> -			sz = 0;
> -			switch (tag & FDT_TAG_DATA_MASK) {
> -			case FDT_TAG_DATA_NONE:
> -				break;
> -			case FDT_TAG_DATA_1CELL:
> -				sz = FDT_CELLSIZE;
> -				break;
> -			case FDT_TAG_DATA_2CELLS:
> -				sz = 2 * FDT_CELLSIZE;
> -				break;
> -			case FDT_TAG_DATA_VARLEN:
> -				/* Get the length */
> -				sz = fdt32_to_cpu(GET_CELL(p));
> -				break;
> -			}
> +			p = get_structured_tag_data(tag, p, &d, &sz);
>  
>  			if (dump_unknown) {
>  				printf("%*s// Unknown tag ignored: 0x%08"PRIx32", data len %d",
> @@ -175,13 +188,10 @@ static void dump_blob(void *blob, bool debug, int dump_unknown)
>  				if (dump_unknown > 1 && sz != 0) {
>  					printf(" ");
>  					for (i = 0; i < sz; i++)
> -						printf("%02hhx", *(p + i));
> +						printf("%02hhx", *(d + i));
>  				}
>  				printf("\n");
>  			}
> -
> -			/* Skip the data bytes */
> -			p = PALIGN(p + sz, 4);
>  			continue;
>  		}
>  
> -- 
> 2.55.0
> 
> 

-- 
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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