[PATCH 3/6] partitions: gpt: factor out a function to write primary/alternate GPT

[Ahmad Fatoum]

On 12/3/25 4:19 PM, Sascha Hauer wrote:
> In preparation for writing the inactive GPT first factor out a function
> which either writes the primary or alternate GPT based on a boolean
> argument.
> 
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>

Reviewed-by: Ahmad Fatoum <a.fatoum at pengutronix.de>

> ---
>  common/partitions/efi.c | 92 ++++++++++++++++++++++++++++---------------------
>  1 file changed, 53 insertions(+), 39 deletions(-)
> 
> diff --git a/common/partitions/efi.c b/common/partitions/efi.c
> index 76c5393dddb04e2966d3a4b4478d5085f008d935..8da62acf36646b62ff2fac25673adbc48650d299 100644
> --- a/common/partitions/efi.c
> +++ b/common/partitions/efi.c
> @@ -740,75 +740,89 @@ static int efi_protective_mbr(struct block_device *blk)
>  	return ret;
>  }
>  
> -static __maybe_unused int efi_partition_write(struct partition_desc *pd)
> +static int __efi_partition_write(struct efi_partition_desc *epd, bool primary)
>  {
> -	struct block_device *blk = pd->blk;
> -	struct efi_partition_desc *epd = container_of(pd, struct efi_partition_desc, pd);
> -	gpt_header *gpt = epd->gpt, *altgpt;
> +	struct block_device *blk = epd->pd.blk;
> +	gpt_header *gpt;
> +	unsigned int count, size;
> +	uint64_t my_lba, partition_entry_lba;
>  	int ret;
> -	uint32_t count;
> -	uint64_t from, size;
>  
> -	if (le32_to_cpu(gpt->num_partition_entries) != 128) {
> -		/*
> -		 * This is not yet properly implemented. At least writing of the
> -		 * alternative GPT is not correctly implemented for this case as
> -		 * we can't assume that the partition entries are written at
> -		 * last_lba() - 32, we would have to calculate that from the number
> -		 * of partition entries.
> -		 */
> -		pr_err("num_partition_entries is != 128. This is not yet supported for writing\n");
> -		return -EINVAL;
> -	}
> +	gpt = xmemdup(epd->gpt, SECTOR_SIZE);
>  
>  	count = le32_to_cpu(gpt->num_partition_entries) *
>  		le32_to_cpu(gpt->sizeof_partition_entry);
>  
> -	gpt->my_lba = cpu_to_le64(1);
> -	gpt->alternate_lba = cpu_to_le64(last_lba(blk));
> +	size = count / GPT_BLOCK_SIZE;
> +
> +	if (primary) {
> +		my_lba = 1;
> +		partition_entry_lba = le64_to_cpu(gpt->partition_entry_lba);
> +		gpt->alternate_lba = cpu_to_le64(last_lba(blk));
> +	} else {
> +		my_lba = last_lba(blk);
> +		partition_entry_lba = last_lba(blk) - 32;
> +		gpt->alternate_lba = cpu_to_le64(1);
> +	}
> +
> +	gpt->my_lba = cpu_to_le64(my_lba);
> +	gpt->partition_entry_lba = cpu_to_le64(partition_entry_lba);
>  	gpt->partition_entry_array_crc32 = cpu_to_le32(efi_crc32(
>  			(const unsigned char *)epd->ptes, count));
>  	gpt->header_crc32 = 0;
>  	gpt->header_crc32 = cpu_to_le32(efi_crc32((const unsigned char *)gpt,
>  						  le32_to_cpu(gpt->header_size)));
>  
> -	ret = efi_protective_mbr(blk);
> +	ret = block_write(blk, gpt, my_lba, 1);
>  	if (ret)
> -		return ret;
> +		goto err_block_write;
>  
> -	ret = block_write(blk, gpt, 1, 1);
> +	ret = block_write(blk, epd->ptes, partition_entry_lba, size);
>  	if (ret)
>  		goto err_block_write;
>  
> -	from = le64_to_cpu(gpt->partition_entry_lba);
> -	size = count / GPT_BLOCK_SIZE;
> +err_block_write:
> +	free(gpt);
>  
> -	ret = block_write(blk, epd->ptes, from, size);
> -	if (ret)
> -		goto err_block_write;
> +	return ret;
> +}
>  
> -	altgpt = xmemdup(gpt, SECTOR_SIZE);
> +static __maybe_unused int efi_partition_write(struct partition_desc *pd)
> +{
> +	struct block_device *blk = pd->blk;
> +	struct efi_partition_desc *epd = container_of(pd, struct efi_partition_desc, pd);
> +	gpt_header *gpt = epd->gpt;
> +	int ret;
>  
> -	altgpt->alternate_lba = cpu_to_le64(1);
> -	altgpt->my_lba = cpu_to_le64(last_lba(blk));
> -	altgpt->partition_entry_lba = cpu_to_le64(last_lba(blk) - 32);
> -	altgpt->header_crc32 = 0;
> -	altgpt->header_crc32 = cpu_to_le32(efi_crc32((const unsigned char *)altgpt,
> -						  le32_to_cpu(altgpt->header_size)));
> -	ret = block_write(blk, altgpt, last_lba(blk), 1);
> +	if (le32_to_cpu(gpt->num_partition_entries) != 128) {
> +		/*
> +		 * This is not yet properly implemented. At least writing of the
> +		 * alternative GPT is not correctly implemented for this case as
> +		 * we can't assume that the partition entries are written at
> +		 * last_lba() - 32, we would have to calculate that from the number
> +		 * of partition entries.
> +		 */
> +		pr_err("num_partition_entries is != 128. This is not yet supported for writing\n");
> +		return -EINVAL;
> +	}
>  
> -	free(altgpt);
> +	ret = efi_protective_mbr(blk);
> +	if (ret)
> +		return ret;
>  
> +	ret = __efi_partition_write(epd, true);
>  	if (ret)
>  		goto err_block_write;
> -	ret = block_write(blk, epd->ptes, last_lba(blk) - 32, size);
> +
> +	ret = __efi_partition_write(epd, false);
>  	if (ret)
>  		goto err_block_write;
>  
> -	return 0;
> +	ret = 0;
>  
>  err_block_write:
> -	pr_err("Cannot write to block device: %pe\n", ERR_PTR(ret));
> +	if (ret)
> +		pr_err("Cannot write to block device: %pe\n", ERR_PTR(ret));
>  
>  	return ret;
>  }
> 

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