Re: [PATCH] erofs: handle 48-bit blocks/uniaddr for extra devices

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2026/4/3 11:34, Zhan Xusheng wrote:
> erofs_init_device() only reads blocks_lo and uniaddr_lo from the
> on-disk device slot, ignoring blocks_hi and uniaddr_hi that were
> introduced alongside the 48-bit block addressing feature.
> 
> For the primary device (dif0), erofs_read_superblock() already handles
> this correctly by combining blocks_lo with blocks_hi when 48-bit
> layout is enabled.  But the same logic was not applied to extra
> devices.
> 
> With a 48-bit EROFS image using extra devices whose uniaddr or blocks
> exceed 32-bit range, the truncated values cause erofs_map_dev() to
> compute wrong physical addresses, leading to silent data corruption.
> 
> Fix this by reading blocks_hi and uniaddr_hi in erofs_init_device()
> when 48-bit layout is enabled, consistent with the primary device
> handling.
> 
> Fixes: 61ba89b57905 ("erofs: add 48-bit block addressing on-disk support")
> Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>

Yeah, it seems that part was never implemented,

but could you fix

__le32 blocks_hi; in `struct erofs_deviceslot` to `__le16` as well?

`blocks_hi` shouldn't be `__le32`.

> ---
> Note: erofs-utils also needs corresponding fixes for the write path
> (erofs_mkfs_format_devices) and a swapped hi/lo read in
> erofs_read_superblock, which will be sent separately.
> ---
>   fs/erofs/super.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 972a0c82198d..a04e70ef4fcc 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -177,6 +177,10 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
>   
>   	dif->blocks = le32_to_cpu(dis->blocks_lo);
>   	dif->uniaddr = le32_to_cpu(dis->uniaddr_lo);
> +	if (erofs_sb_has_48bit(sbi)) {
> +		dif->blocks |= (u64)le32_to_cpu(dis->blocks_hi) << 32;
> +		dif->uniaddr |= (u64)le16_to_cpu(dis->uniaddr_hi) << 32;
> +	}

Maybe just

	bool _48bit = erofs_sb_has_48bit(sbi);

	..

	dif->blocks = le32_to_cpu(dis->blocks_lo) |
		(_48bit ? (u64)le16_to_cpu(dis->blocks_hi) << 32 : 0);
	dif->uniaddr = le32_to_cpu(dis->uniaddr_lo) |
		(_48bit ? (u64)le16_to_cpu(dis->uniaddr_hi) << 32 : 0);

Thanks,
Gao Xiang