Re: [PATCH] erofs-utils: lib: fix erofs_is_packed_inode() on the read path

[Gao Xiang <xiang@kernel.org>]

Hi Seula,

On Thu, Aug 13, 2026 at 06:38:49PM +0900, seula2.lee@lge.com wrote:
> From: Seula Lee <seula2.lee@lge.com>
> 
> erofs_is_packed_inode() compares i_srcpath against the global
> EROFS_PACKED_INODE identifier.  i_srcpath is only assigned by
> mkfs.erofs and has no on-disk counterpart, so it is never set for
> inodes filled in by erofs_read_inode_from_disk(), and the helper always
> returns false on the read path.
> 
> fsck.erofs therefore treats the packed inode as an ordinary regular
> file at all four of its call sites, for any image with fragments and a
> non-zero packed_nid:
> 
> - erofsfsck_extract_inode(): the guard never fires, so
> erofs_extract_file() writes the packed data to fsckcfg.extract_path
> itself, which is still the top-level directory because main()
> checks the packed inode before the root inode. Extracting the root
> then fails in erofs_extract_dir():
> 
> $ mkfs.erofs -zlz4hc -Efragments img.erofs dir
> $ fsck.erofs --extract=out img.erofs
> <E> erofs: erofs_extract_dir() Line[697] path is not a directory: out
> <E> erofs: main() Line[1256] Failed to extract filesystem
> $ file out
> out: ASCII text # 603720 bytes, the packed inode itself
> 
> - erofsfsck_set_attributes(): the packed inode's mode, timestamps and
> xattrs are applied to the extraction root directory.
> 
> - erofs_verify_inode_data(): the packed inode's own compressed data is
> decoded and hashed as if it were file data.
> 
> - the -p accounting: fragment bytes are counted both as file data and
> as packed inode data, so the reported ratio is too low.
> 
> Restore the nid-based test, which is how the packed inode is already
> identified elsewhere on the read path: z_erofs_read_one_data() compares
> inode->nid against sbi->packed_nid directly, and the
> erofs_sb_has_fragments(sbi) && sbi->packed_nid > 0 idiom used here is
> the same one in fuse/main.c, dump/main.c and fsck.erofs' own
> erofs_packedfile_init() call.
> 
> The i_srcpath comparison has to stay first rather than be replaced:
> while mkfs.erofs builds the packed inode its nid is still
> EROFS_NID_UNALLOCATED and sbi->packed_nid is 0, so a nid-only test
> would return false there and break fragment dedupe and
> pclusterblks_packed handling in lib/compress.c.
> 
> This restores the v1.8.x behaviour at every call site, where the helper
> was nid-based; in particular the packed inode is again excluded from the
> decompression check that --extract performs, as it was before v1.9.
> 
> dump.erofs is affected the same way and prints "Path : (packed file)"
> again as intended.
> 
> erofs_is_metabox_inode() shares the same idiom, but it has no read-path
> caller (all callers are in lib/compress.c and lib/inode.c), so it is
> left alone.
> 
> Fixes: 7928074b7643 ("erofs-utils: introduce metadata compression [metabox]")
> Signed-off-by: Seula Lee <seula2.lee@lge.com>

Thanks for the patch, that is indeed a bug and the fix looks fine,
but the commit message is too long to understand the impacts (it seems
in a LLM-generated-style.)

I will rephrase a short commit message instead.

Thanks,
Gao Xiang