Re: [PATCH v2 4/5] erofs-utils: mfks: add rebuild FULLDATA for combined EROFS images

[Gao Xiang <xiang@kernel.org>]

Hi Lucas,

On Mon, Mar 09, 2026 at 12:38:20PM -0400, Lucas Karpinski wrote:
> This patch introduces experimental support for merging multiple source
> images in mkfs. Each source image becomes a directory directly under root
> and keeps its UUID stored as a device table tag. The raw block data from
> each source is copied using erofs_copy_file_range. We preserve the file
> metadata and layout (FLAT_PLAIN and FLAT_INLINE). Symlink paths are handled
> by reading and copy link targets.
> 
> This does not yet support chunk-based files at this time or compressed
> images.
> 
> Signed-off-by: Lucas Karpinski <lkarpinski@nvidia.com>

Thanks for your effort, I finally get the time to look into this
new feature.

So you'd like to cleanly rebuild a new filesystem with given sub
filesystems?

I think first, yes, that is what `--clean=data` is used instead.

But I think uniaddr shouldn't be used like this (uniaddr is used to
give a flat mapping for multiple blobs, in addition to the device id +
offset ones, which is mainly used for compressed data multi blob
support), instead, I think we need to find a way to wrap up the data
source into a valid vfile (so that erofs_pread can be called to get the
source data) , and make erofs_mkfs_job_write_file() to write
(un)compressed data from its source instead.

Thanks,
Gao Xiang