linux-kernel - [QUESTION vfs] Namespaces from kernel code for user mode threads

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Message-ID: <20250430144436-d3c2c91d-b32e-4967-96c9-3913579ce626@linutronix.de>
Date: Wed, 30 Apr 2025 15:05:04 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Christian Brauner <brauner@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>
Cc: Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [QUESTION vfs] Namespaces from kernel code for user mode threads

Hi everybody,

I am trying to set up mount namespaces on top of a 'struct vfsmount'
and run user mode threads inside that namespace. All of this from kernel code.
However there doesn't seem a way to run the equivalent of unshare(CLONE_NEWNS)
inside the kernel.
Is this something that should work and if so, how?
The goal is that these processes execute inside a nearly empty filesystem tree.

The full context is in this series:
https://lore.kernel.org/all/20250217-kunit-kselftests-v1-0-42b4524c3b0a@linutronix.de/
Specifically "[PATCH 09/12] kunit: Introduce UAPI testing framework"
in kunit_uapi_mount_tmpfs() and related.

Thanks,
Thomas