[PATCH] blobchunk: fix 48-bit format detection to use final remapped block addresses

[Gao Xiang]

Hi puneeth_aditya_5656,

Could you format the commit message instead of leaving
the commit message empty (maximum 72 chars per line).

The subject needs to be fixed as:

erofs-utils: lib: fix 48bit addressing detection for chunk-based format

On 2026/2/24 13:57, puneeth_aditya_5656 wrote:
> ---
>   lib/blobchunk.c | 17 +++++++++++++----
>   1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/blobchunk.c b/lib/blobchunk.c
> index a051904..9b8112b 100644
> --- a/lib/blobchunk.c
> +++ b/lib/blobchunk.c
> @@ -154,6 +154,19 @@ int erofs_write_chunk_indexes(struct erofs_inode *inode, struct erofs_vfile *vf,
>   		unit = EROFS_BLOCK_MAP_ENTRY_SIZE;
>   
>   	chunkblks = 1ULL << (inode->u.chunkformat & EROFS_CHUNK_FORMAT_BLKBITS_MASK);
> +
> +	/* check if any chunk lands above 32-bit range once remapped_base is applied */
> +	for (src = 0; src < inode->extent_isize / unit * sizeof(void *);


I think it's too late to adjust inode->u.chunkformat,
see erofs_iflush():

I think you currently just add a new function like:

erofs_inode_fixup_chunkformat() {

	u64 extent_count = inode->extent_isize / unit;

	_48bit = inode->u.chunkformat & EROFS_CHUNK_FORMAT_48BIT;
	if (_48bit)
		return;

	for (src = 0; src < extent_count; ++src) {
		if (chunk->blkaddr == EROFS_NULL_ADDR)
			continue;
		if (chunk->device_id) {
			if (chunk->blkaddr > UINT32_MAX) {
				_48bit = true;
				break;
			}
		} else if (remapped_base + chunk->blkaddr > UINT32_MAX) {
			_48bit = true;
			break;
		}
	}
	if (_48bit)
		inode->u.chunkformat |= EROFS_CHUNK_FORMAT_48BIT;
}

Also if we really would like to fix this, we need considering add
a testcase for this, possibly use `--offset` to make the image
exceeds 32-bit, see experimental-tests.

Thanks,
Gao Xiang