Message-ID: <25234476-2011-4ade-affe-687d45dcbc3c@tnxip.de>
Date: Wed, 21 May 2025 13:26:55 +0200
From: Malte Schröder <malte.schroeder@...ip.de>
To: John Stoffel <john@...ffel.org>,
 Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Amir Goldstein <amir73il@...il.com>, linux-fsdevel@...r.kernel.org,
 linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-unionfs@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 0/6] overlayfs + casefolding

On 20/05/2025 20:49, John Stoffel wrote:
>>>>>> "Kent" == Kent Overstreet <kent.overstreet@...ux.dev> writes:
>> On Tue, May 20, 2025 at 04:03:27PM +0200, Amir Goldstein wrote:
>>> On Tue, May 20, 2025 at 2:43 PM Kent Overstreet
>>> <kent.overstreet@...ux.dev> wrote:
>>>> On Tue, May 20, 2025 at 02:40:07PM +0200, Amir Goldstein wrote:
>>>>> On Tue, May 20, 2025 at 2:25 PM Kent Overstreet
>>>>> <kent.overstreet@...ux.dev> wrote:
>>>>>> On Tue, May 20, 2025 at 10:05:14AM +0200, Amir Goldstein wrote:
>>>>>>> On Tue, May 20, 2025 at 7:16 AM Kent Overstreet
>>>>>>> <kent.overstreet@...ux.dev> wrote:
>>>>>>>> This series allows overlayfs and casefolding to safely be used on the
>>>>>>>> same filesystem by providing exclusion to ensure that overlayfs never
>>>>>>>> has to deal with casefolded directories.
>>>>>>>>
>>>>>>>> Currently, overlayfs can't be used _at all_ if a filesystem even
>>>>>>>> supports casefolding, which is really nasty for users.
>>>>>>>>
>>>>>>>> Components:
>>>>>>>>
>>>>>>>> - filesystem has to track, for each directory, "does any _descendent_
>>>>>>>>   have casefolding enabled"
>>>>>>>>
>>>>>>>> - new inode flag to pass this to VFS layer
>>>>>>>>
>>>>>>>> - new dcache methods for providing refs for overlayfs, and filesystem
>>>>>>>>   methods for safely clearing this flag
>>>>>>>>
>>>>>>>> - new superblock flag for indicating to overlayfs & dcache "filesystem
>>>>>>>>   supports casefolding, it's safe to use provided new dcache methods are
>>>>>>>>   used"
>>>>>>>>
>>>>>>> I don't think that this is really needed.
>>>>>>>
>>>>>>> Too bad you did not ask before going through the trouble of this implementation.
>>>>>>>
>>>>>>> I think it is enough for overlayfs to know the THIS directory has no
>>>>>>> casefolding.
>>>>>> overlayfs works on trees, not directories...
>>>>> I know how overlayfs works...
>>>>>
>>>>> I've explained why I don't think that sanitizing the entire tree is needed
>>>>> for creating overlayfs over a filesystem that may enable casefolding
>>>>> on some of its directories.
>>>> So, you want to move error checking from mount time, where we _just_
>>>> did a massive API rework so that we can return errors in a way that
>>>> users will actually see them - to open/lookup, where all we have are a
>>>> small fixed set of error codes?
>>> That's one way of putting it.
>>>
>>> Please explain the use case.
>>>
>>> When is overlayfs created over a subtree that is only partially case folded?
>>> Is that really so common that a mount time error justifies all the vfs
>>> infrastructure involved?
>> Amir, you've got two widely used filesystem features that conflict and
>> can't be used on the same filesystem.
> Wait, what?  How many people use casefolding, on a per-directory
> basis?  It's stupid.  Unix/Linux has used case-sensitive filesystems
> for years.  Yes, linux supports other OSes which did do casefolding,
> but yikes... per-directory support is just insane.  It should be
> per-filesystem only at BEST.  
>
>> That's _broken_.
> So?  what about my cross mounting of VMS filesystems with "foo.txt;3"
> version control so I can go back to previous versions?  Why can't I do
> that from my Linux systems that's mounting that VMS image?   
>
> Just because it's done doesn't mean it's not dumb.  
>
>> Users hate partitioning just for separate /boot and /home, having to
>> partition for different applications is horrible. And since overlay
>> fs is used under the hood by docker, and casefolding is used under
>> the hood for running Windows applications, this isn't something
>> people can predict in advance.
> Sure I can, I don't run windows applications to screw casefolding.
> :-)
>
> And I personally LIKE having a seperate /boot and /home, because it
> gives isolation.  The world is not just single user laptops with
> everything all on one disk or spread across a couple of disks using
> LVM or RAID or all of the above.  
>
> I also don't see any updates for the XFS tests, or any other
> filesystem tests, that actually checks and confirms this decidedly
> obtuse and dumb to implement idea.  
>
>
> John
>
Hi there,

would you partition different subdirs of your /home? So there is
.local/share/containers where users put their container-stuff (at least
podman does). Then there is .wine where case-folding-craziness lives.
And then there is the mess that is Steam, which does all kinds of
containery case-foldy stuff. As much as I would like to keep these
things apart, it is not feasible. Not for me as a "power user", and
certainly far out of reach for average Joe user.

Just my 2 ct, greets

/Malte

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