When and why to deprecate filesystems [LWN.net]

When and why to deprecate filesystems

Posted Mar 17, 2022 14:23 UTC (Thu) by mrugiero (guest, #153040)
Parent article: When and why to deprecate filesystems

The only thing I can say is that a mandatory part of the deprecation process of filesystems should be to implement a FUSE driver for them. You never know when you'll need to access an ancient drive to recover data, and that should be enough to cover that case.
It could be a subtree in the kernel tree or a sister project under the Linux Foundation umbrella, but with a policy that you can't deprecate the kernel driver without that in place.
A simplification could be to only implement read features. Then when it gets obsoleted we still can access archives.

to post comments

When and why to deprecate filesystems

Posted Mar 17, 2022 18:25 UTC (Thu) by rmano (guest, #49886) [Link] (1 responses)

I agree (at least in principle... The part on who should do it is a problem :-)).

I still have CD-ROM burned in extfs around from the '90. The good part is that I don't think that I'll need them ever...

When and why to deprecate filesystems

Posted Mar 17, 2022 20:58 UTC (Thu) by mrugiero (guest, #153040) [Link]

> The part on who should do it is a problem :-)

Well, the one who wants to deprecate should make sure the replacement is in place, IMO :) (Which doesn't necessarily means doing it themselves, but at least finding someone)
Besides, testing FUSE filesystems could possibly be done with a single test suite ran much less often as the code is expected to change less.
Another idea to add work to someone else (TM) would be to require this to introduce new filesystems. It'd be nice to other OSes to be able to read whatever Linux brings and it would make it trivial to deprecate them later, as it's much easier to write this when the know-how is already in your head rather than reverse engineering the work someone did 20 years ago.

When and why to deprecate filesystems

Posted Mar 18, 2022 4:04 UTC (Fri) by pabs (subscriber, #43278) [Link] (1 responses)

I'm looking forward to the Linux Kernel Library project being merged, that would probably allow using all Linux kernel filesystem code in userspace, then you could add a FUSE wrapper for them.

When and why to deprecate filesystems

Posted Mar 18, 2022 8:20 UTC (Fri) by smurf (subscriber, #17840) [Link]

That doesn't help much. In the distant future you won't be able to compile then-ancient kernels (i.e. those with reiserfs still in them) with then-current compilers, just like you can't compile now-ancient kernels with gcc 12.

It doesn't matter (much) whether that kernel shall compile to a mere FUSE helper that exports a reiserfs file system, or a full-blown kernel you'd run in a VM (mount the reiserfs image there and export it to the host via NFS or CIFS). Assuming it'll work in that then-current VM; that's mostly likely, IMHO, but by no means assured.

The solution is (assuming that there is no reiserfs support library you can use a shortcut) to extract a libreiserfs from the kernel and remove all the kernel idiosyncrasies from it. At that point it's standard C plus libfuse and thus presumably easier to keep up-to-date with whatever fun incompatibilities the C and/or FUSE people will throw in your path in the future.

When and why to deprecate filesystems

Posted Mar 18, 2022 13:40 UTC (Fri) by HelloWorld (guest, #56129) [Link] (2 responses)

That's ridiculous. We're talking about a significant engineering effort for something that is going to be used exceedingly rarely. And it's completely unnecessary too, because there's an obvious solution for recovering the data: just run an older kernel in a VM and copy the data over.

When and why to deprecate filesystems

Posted Mar 18, 2022 14:49 UTC (Fri) by mrugiero (guest, #153040) [Link] (1 responses)

Suppose there comes a point where the intersection between supported filesystems is empty (we'll reach that point eventually, ext4 and btrfs will eventually be obsolete too), how would you copy from reiserfs to an actually living filesystem? Mounting in 7 other kernels?

When and why to deprecate filesystems

Posted Mar 18, 2022 16:49 UTC (Fri) by farnz (subscriber, #17727) [Link]

Something like tar or rsync over the hypervisor's networking would work just fine. After all, I can tar up a filesystem on a 1980s vintage UNIX system, or run PKZIP on a 1980s vintage DOS system, and uncompress the resulting archive on a modern Linux PC.

When and why to deprecate filesystems

Posted Mar 20, 2022 7:50 UTC (Sun) by Shabbyx (guest, #104730) [Link]

If the problem is recovering an old archive... Well just use an old kernel (in an old distro) for that half an hour you need to copy the data out. The scenario you are describing is an unlikely and a one-time event. Why bother with developing, testing and maintaing something for that one time you might need it when an old kernel would do?