[PATCH] mkfs: support block map for blob devices

[zhaoyifan (H)]

On 2026/3/7 14:28, Nithurshen wrote:
> Currently, using --blobdev to specify an extra device is restricted from working with the block map chunk format. This was previously noted as a task that could be implemented by mapping the device blocks using a global address.
>
> This patch implements this support by allowing the block map to reference chunks residing on extra devices. This is achieved by:
> 	1) Removing the -EINVAL check in mkfs/main.c that blocked this combination of flags.
> 	2) Calculating the global startblk address for the block map by summing the blocks of the primary device and any preceding extra devices.
> 	3) Ensuring that EROFS_CHUNK_FORMAT_INDEXES is only set if the user has not forced the block map format, and adjusting the index unit size to EROFS_BLOCK_MAP_ENTRY_SIZE accordingly.
> 	4) Updating erofs_inode_fixup_chunkformat to correctly identify when 48-bit addressing is required for a block-mapped file on an extra device.

Hi Nithurshen,

Each line of the commit message must not exceed 72 characters.

> Signed-off-by: Nithurshen <nithurshen.dev at gmail.com>
> ---
>   lib/blobchunk.c | 34 ++++++++++++++++++++++++++++------
>   mkfs/main.c     |  7 -------
>   2 files changed, 28 insertions(+), 13 deletions(-)
>
> diff --git a/lib/blobchunk.c b/lib/blobchunk.c
> index 96c161b..2ef7462 100644
> --- a/lib/blobchunk.c
> +++ b/lib/blobchunk.c
> @@ -159,7 +159,17 @@ void erofs_inode_fixup_chunkformat(struct erofs_inode *inode)
>   		if (chunk->blkaddr == EROFS_NULL_ADDR)
>   			continue;
>   		if (chunk->device_id) {
> -			if (chunk->blkaddr > UINT32_MAX) {
> +			if (!(inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES)) {
> +				erofs_blk_t mapped_blkaddr = inode->sbi->primarydevice_blocks;
> +				unsigned int i;
> +
> +				for (i = 0; i < chunk->device_id - 1; i++)
> +					mapped_blkaddr += inode->sbi->devs[i].blocks;
> +				if (mapped_blkaddr + chunk->blkaddr > UINT32_MAX) {
> +					_48bit = true;

It's impossible for 32-bit block map entries to support 48bit mode.

I think we should err out instead of enabling 48bit here.


BTW, it seems the erofs-utils codebase could not read a chunk-based 
EROFS image

with block map and extra devices (but in-kernel implementation could), 
as erofs_map_dev() does

not reset m_deviceid. Could you help also fix this? If you are 
interested please also add related

testcases in erofs/erofsnightly repo.


Thanks,

Yifan Zhao

> +					break;
> +				}
> +			} else if (chunk->blkaddr > UINT32_MAX) {
>   				_48bit = true;
>   				break;
>   			}
> @@ -201,8 +211,16 @@ int erofs_write_chunk_indexes(struct erofs_inode *inode, struct erofs_vfile *vf,
>   		if (chunk->blkaddr == EROFS_NULL_ADDR) {
>   			startblk = EROFS_NULL_ADDR;
>   		} else if (chunk->device_id) {
> -			DBG_BUGON(!(inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES));
> -			startblk = chunk->blkaddr;
> +			if (inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES) {
> +				startblk = chunk->blkaddr;
> +			} else {
> +				unsigned int i;
> +
> +				startblk = sbi->primarydevice_blocks;
> +				for (i = 0; i < chunk->device_id - 1; i++)
> +					startblk += sbi->devs[i].blocks;
> +				startblk += chunk->blkaddr;
> +			}
>   			extent_start = EROFS_NULL_ADDR;
>   		} else {
>   			startblk = remapped_base + chunk->blkaddr;
> @@ -324,7 +342,7 @@ int erofs_blob_write_chunked_file(struct erofs_inode *inode, int fd,
>   	chunksize = 1ULL << chunkbits;
>   	count = DIV_ROUND_UP(inode->i_size, chunksize);
>   
> -	if (sbi->extra_devices)
> +	if (sbi->extra_devices && cfg.c_force_chunkformat != FORCE_INODE_BLOCK_MAP)
>   		inode->u.chunkformat |= EROFS_CHUNK_FORMAT_INDEXES;
>   	if (inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES)
>   		unit = sizeof(struct erofs_inode_chunk_index);
> @@ -494,8 +512,12 @@ int tarerofs_write_chunkes(struct erofs_inode *inode, erofs_off_t data_offset)
>   	inode->u.chunkformat |= chunkbits - sbi->blkszbits;
>   	if (sbi->extra_devices) {
>   		device_id = 1;
> -		inode->u.chunkformat |= EROFS_CHUNK_FORMAT_INDEXES;
> -		unit = sizeof(struct erofs_inode_chunk_index);
> +		if (cfg.c_force_chunkformat != FORCE_INODE_BLOCK_MAP)
> +			inode->u.chunkformat |= EROFS_CHUNK_FORMAT_INDEXES;
> +		if (inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES)
> +			unit = sizeof(struct erofs_inode_chunk_index);
> +		else
> +			unit = EROFS_BLOCK_MAP_ENTRY_SIZE;
>   		DBG_BUGON(erofs_blkoff(sbi, data_offset));
>   		blkaddr = erofs_blknr(sbi, data_offset);
>   	} else {
> diff --git a/mkfs/main.c b/mkfs/main.c
> index 58c18f9..07ef086 100644
> --- a/mkfs/main.c
> +++ b/mkfs/main.c
> @@ -1565,13 +1565,6 @@ static int mkfs_parse_options_cfg(struct erofs_importer_params *params,
>   		return -EINVAL;
>   	}
>   
> -	/* TODO: can be implemented with (deviceslot) mapped_blkaddr */
> -	if (cfg.c_blobdev_path &&
> -	    cfg.c_force_chunkformat == FORCE_INODE_BLOCK_MAP) {
> -		erofs_err("--blobdev cannot work with block map currently");
> -		return -EINVAL;
> -	}
> -
>   	if (optind >= argc) {
>   		erofs_err("missing argument: FILE");
>   		return -EINVAL;