UML mount failure with Linux 6.11

[Benjamin Berg]

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.

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.

Benjamin

On Wed, 2024-10-30 at 13:43 +0530, Ritesh Raj Sarraf wrote:
> Hello,
> 
> 
> Recently I updated the UML package to Linux 6.11 in Debian. Upon it,
> it
> reports the below regression wherein UML cannot mount file systems of
> type hostfs
> 
> We have it reported on the Debian bug tracker as well.
> 
> * https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1086194
> 
> 
> The mount failures report as:
> 
> ```
> Oct 30 05:57:41 uml systemd[1]: Mounting usr-lib-modules.mount -
> /usr/lib/modules...
> Oct 30 05:57:42 uml systemd[1]: usr-lib-modules.mount: Mount process
> exited, code=exited, status=32/n/a
> Oct 30 05:57:42 uml mount[814]: mount: /usr/lib/modules: fsconfig
> system call failed: hostfs: Unknown parameter '/usr/lib/uml/modules'.
> Oct 30 05:57:42 uml mount[814]:        dmesg(1) may have more
> information after failed mount system call.
> Oct 30 05:57:42 uml systemd[1]: usr-lib-modules.mount: Failed with
> result 'exit-code'.
> Oct 30 05:57:42 uml systemd[1]: Failed to mount usr-lib-modules.mount
> - /usr/lib/modules.
> 
> ```
> 
> As I understand it, the issue was first seen in July, around 6.11
> rc1.
> 
> *
> https://lore.kernel.org/all/CAHk-=wjH5uKPB6xrWoB8WkBMuLEJO2UsidKE1wV8XSXjAUFO8Q@mail.gmail.com/
> 
> 
> Thanks,
> Ritesh
>