Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Gao Xiang <xiang@kernel.org>]

Hi Greg,

On Tue, Oct 13, 2026 at 09:59:58AM +0200, Greg KH wrote:
> On Tue, Oct 13, 2026 at 09:28:44AM +0200, Gao Xiang wrote:
> > Hi Sasha,
> > 
> > I'm not sure why we need to backport this into stable kernels, as there
> > are users who use EROFS over fscache on these stable kernels.
> > 
> > The functionality works and it's a breaking change.  Could you please
> > kindly tell why?
> 
> Why would you have a breaking change in Linus's tree?  We never break
> existing users, so how was this ever accepted in mainline?

Because the similar + better functionality "erofs over fanotify" is
already available in the recent upstream, and it has simpler interfaces
than "erofs over fscache.", so we don't actually break users as long
as one of those functionalities exist ("erofs over fanotify" or
"erofs over fscache".  Many stable kernels don't support "erofs over
fsnotify", so backport this commit will make existing users using
old stable kernels have no choice (no "erofs over fanotify" nor
"erofs over fscache").

The commit message is already described well I think. 

> 
> As this removal fixes known bugs, isn't that a good thing for those
> older users as well?  Why would you want them to run broken systems?

I think it depends on the importance of the bug, at least "erofs over
fscache" is usable (and it's used by vendors) on stable kernels, but
it's unneeded to address every edge case found by LLMs since I mostly
think it doesn't impact the real use case, and as I said, we have
a new unique interface ("erofs over fanotify") now, but only on very
latest kernels.

Also there could always be breaking changes for various reasons (e.g.
obsolete/dispute filesystem breaking changes these years like
bcachefs, etc), will these commits be backported to all stable kernels
too?

Thanks,
Gao Xiang


>
> thanks,
> 
> greg k-h
>