Re: [PATCH -RFC] ext4: add feature file to advertise that ext4 supports idmapped mounts

Christian Brauner
2021-04-15T08:13:26Z

On Thu, Apr 15, 2021 at 09:55:37AM +0200, Christoph Hellwig wrote:
> On Thu, Apr 15, 2021 at 09:49:21AM +0200, Christian Brauner wrote:
> > However, as a general way of advertising to users that ext4 supports
> > idmapped mounts I don't necessarily see a problem with that. It doesn't
> > have implications for other filesystems and ext4 already advertises
> > other features in a similar way.
>
> I still think that is a very bad idea. idmapped mounts are foremost
> a VFS feature, with just a tiny bit of glue in every file system that
> does not affect the on-disk format. So any discovery for it needs
> to be using VFS infrastructure. IMHO just trying to mount is the
> proper way to do it, but if people want some other form of discovery
> it needs to be something in generic code.

I agree with you there.
I think fsinfo() (Arguably a slimmed-down version of it.) would've been
the best place for this.