linux-kernel - Re: [PATCH v15 5/9] erofs: introduce the page cache share feature

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Message-ID: <20260120-neuland-rastplatz-31cc7d61a196@brauner>
Date: Tue, 20 Jan 2026 14:40:50 +0100
From: Christian Brauner <brauner@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Gao Xiang <hsiangkao@...ux.alibaba.com>, 
	Hongbo Li <lihongbo22@...wei.com>, chao@...nel.org, djwong@...nel.org, amir73il@...il.com, 
	linux-fsdevel@...r.kernel.org, linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org, 
	Linus Torvalds <torvalds@...ux-foundation.org>, oliver.yang@...ux.alibaba.com
Subject: Re: [PATCH v15 5/9] erofs: introduce the page cache share feature

On Tue, Jan 20, 2026 at 07:52:42AM +0100, Christoph Hellwig wrote:
> On Tue, Jan 20, 2026 at 11:07:48AM +0800, Gao Xiang wrote:
> >
> > Hi Christoph,
> >
> > Sorry I didn't phrase things clearly earlier, but I'd still
> > like to explain the whole idea, as this feature is clearly
> > useful for containerization. I hope we can reach agreement
> > on the page cache sharing feature: Christian agreed on this
> > feature (and I hope still):
> >
> > https://lore.kernel.org/linux-fsdevel/20260112-begreifbar-hasten-da396ac2759b@brauner
> 
> He has to ultimatively decide.  I do have an uneasy feeling about this.
> It's not super informed as I can keep up, and I'm not the one in charge,
> but I hope it is helpful to share my perspective.

It always is helpful, Christoph! I appreciate your input.

I'm fine with this feature. But as I've said in person: I still oppose
making any block-based filesystem mountable in unprivileged containers
without any sort of trust mechanism.

I am however open in the future for block devices protected by dm-verity
with the root hash signed by a sufficiently trusted key to be mountable
in unprivileged containers.