[Parted-maintainers] Bug#1103454: libparted detects ext4 without journal as ext2

[Pascal Hambourg]

On 30/05/2025 at 13:01, Colin Watson wrote:
> On Fri, May 30, 2025 at 12:11:44PM +0200, Pascal Hambourg wrote:
>> On 17/04/2025 at 21:51, Colin Watson wrote:
>>> libparted wrongly detects ext4 without journal as ext2 instead of ext4.
>> (...)
>>> This bug affects the debian installer partitioning tool, partman, which
>>> relies on libparted to detect partition filesystem types. partman
>>> accepts to use such ext4 partition (without formatting it) only as
>>> ext2, then tries and fails to mount it as ext2 because of incompatible
>>> features.
>>
>> Note: this is not a theoretical bug, it was reported by an affected D- 
>> I user in #debian-boot IRC channel.
> 
> If it's a non-trivial bug, why did you file it as Severity: minor? 
> https://www.debian.org/Bugs/Developer#severities - "a problem which 
> doesn't affect the package's usefulness, and is presumably trivial to 
> fix".  It's usually for things like typos.

I am no expert in bug severity assessment, and it seems to me that the 
bug matches the above definition quite well: it does not affect parted's 
overall usefulness, affects only uncommon use cases (d-i + ext4 without 
journal) and is rather trivial to fix (reorder filesystem feature checks).

> Please can you summarize the real-world situation in which this came up? 
> To me this seems like a very niche sort of situation, but if you could 
> actually explain it then that might help.

If you have IRC logs, the discussion took place on April 17th. Quoting 
the OP "Salv"'s report:

"I need to use existing partition and filesystem because I have some fs 
format switches to keep. My root is a ext4 fs formatted with "-m 0 -O 
^has_journal,^resize_inode,^quota -E stride=64,stripe-width=64 -T news", 
but latest testing debian installer (weekly buid) recognizes that 
partition as ext2. Try to workaround: if I try to select ext2 with 
no-format option, in the next step it will fail to mount and fail to 
continue install Debian. If I select ext4 fs, it will just format 
without keeping data."

>> Upstream reviewed the patch and intends to merge it soon [1] but I 
>> guess it is already too late for trixie release.
>>
>> [1] <https://alioth-lists.debian.net/pipermail/parted-devel/2025- 
>> May/005930.html>

The patch is now merged upstream with commit e61584dd.

>> A plan B for trixie release is to add a workaround in partman-base to 
>> double-check the filesystem type with blkid or other available tool 
>> when the filesystem detected by parted_server is ext2.
> 
> I don't think it makes sense to resort to plan B.  Either it should be 
> fixed in parted or it should just be put off until forky.  My question 
> is whether it's worth fixing in trixie at all (never mind a bookworm 
> point release) given what so far has been very sparse information about 
> its actual real-world impact.

This is why I started this discussion.