UML mount failure with Linux 6.11

[Benjamin Berg]

Hi,

I am probably not the right person to talk to. Maybe Hongbo Li can say
more?

That said, it looks like the filesystem now has the "hostfs" option. So
you can probably just use
  mount -t hostfs -o hostfs=/path none /mount/point
which is nicer anyway. Just a bit annoying as you probably need to pass
it differently for older kernels.

Benjamin

On Wed, 2024-11-06 at 17:22 +0530, Ritesh Raj Sarraf wrote:
> Hello Benjamin,
> 
> On Thu, 2024-10-31 at 11:07 +0100, Benjamin Berg wrote:
> > Hi,
> > 
> > Newer kernels have become more picky about that with the new mount
> > API.
> > This is relevant, see the discussion about "Unknown options":
> >   https://lwn.net/Articles/979166/
> > 
> > We only use hostfs for the root file system and in that case it
> > works
> > well if you pass the path using "hostfs=/path" on the kernel
> > command
> > line. Doing that avoids issues when remounting the file system
> > later
> > on.
> > 
> 
> As upstream developers for UML, what would you conclude it as ?
> 
> We've recommended using hostfs for the UML kernel modules as well.
> What
> would be the alternate approach to ensuring a proper boot for a
> modular
> UML kernel ?
> 
> 
> > I suppose that currently it does not work to mount hostfs later on.
> > No
> > idea what the right fix is. Maybe the host directory should be an
> > explicit option like "hostpath=..." or so to make it compatible
> > with
> > the new mount APIs.
> 
> The ability to mount any hostfs mount point was/is a feature provided
> by UML. We've used it and integrated with many tools like debos,
> fakemachine etc; the Debian bug report has the details.
> 
> There'll be more reports following once UML 6.11 hits Debian Testing.
> 
> I hadn't expected a working feature to break with a newer Linux
> release. :-(
> 
> Thanks,
> Ritesh
>