From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C1D0036826B; Thu, 25 Jun 2026 01:10:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782349832; cv=none; b=BoT6m3lCE8kev44SAPEjwAR3ogieNq2Kp57L4xwzpQVx8Sa0k66kKn32Uf4rFtCSiT7VHRr1jT5dVMGiy02QQF28Is72jOZa1Px1qEmYtZIiYkjh82RioaU+BfltgjhAyVgYffcOWf0toQXmlY8Yo2baarB0vGWIQFNG3PUFXwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782349832; c=relaxed/simple; bh=CqwfMqI7Lr/nMU8ct+Xrq+khEb3WLP3QzcepDFSZkM8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ovOtYoXI+LgaYOV/9pvs7v/TVlNm6GvIFny+ItkCgPy/lX72MtwbXZnzU8H2z17KbcfDbX995U6WnmTyDNpru8PY7YXznLZ3PL6ol4BcIxP2lJ3oS0XggcX1IisRJYjTtK6NMqm7yQXlczy4klxAduX7ZR1Ost7yWkxgJU1fonA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=lS0jlFVy; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="lS0jlFVy" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=hYRs/fxYUnkXklcro/L2vZevBsDfMonAZUv31Sq9qQ8=; b=lS0jlFVy0HdzioRFRFJPBGvCLn Rvc1kh+NFMzO9UpMKeuX62GqobexdfhY/1LvkMFgSVHa5L4tgjY/NEPSQsVyp3FuLlHXbojkiKGBg FsAEASiDPwIH+atpDSROOPztQp6ns5FyjiQ7ht04Z8rQjH1cEiaYPm7S9qJzrpARU1VXpyj0GKknj gapNPLw8tYCmmmcEwKytAS6AUqe86o+p8t8JtF0rym6i/W3zSmjaoJ7bcR0e/izJWvp3phGInMMWy Wt9jtDLPNahr4h+cQ38Jp6vqUQAR0MVwLJaIOere/KF4Iy4uXCEX06H045Ly9pm4GWsroazib5oW7 S08E/BxQ==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.99.4 #2 (Red Hat Linux)) id 1wcYbn-0000000Ce4N-3caE; Thu, 25 Jun 2026 01:10:23 +0000 Date: Thu, 25 Jun 2026 02:10:23 +0100 From: Al Viro To: John Ericson Cc: Andy Lutomirski , Li Chen , Cong Wang , Christian Brauner , linux-arch , LKML , linux-fsdevel , linux-api , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Jan Kara , Jonathan Corbet , Shuah Khan , Kees Cook , Sergei Zimmerman , Farid Zakaria Subject: Re: [RFC] Null Namespaces Message-ID: <20260625011023.GM2636677@ZenIV> References: <103524f8-1658-41df-88e9-cf49c628a721@app.fastmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <103524f8-1658-41df-88e9-cf49c628a721@app.fastmail.com> Sender: Al Viro On Wed, Jun 24, 2026 at 07:53:53PM -0400, John Ericson wrote: > I wanted to discuss a bit about each type of namespace to indicate that > this is a concept I think works across the board --- it wouldn't be such > a good solution for the process spawning API if it was only applicable > to some but not all namespace types. But the truth is that I have > thought about the FS cases the most, as I think you have picked up on. > > If there is interest in landing > > 1. null CWD > 2. null root fs > 3. null mount namespace > > in isolation, and then returning to the other namespaces to iron out > their details, that would be fantastic. It would be much nicer for me to > get some momentum that way, without having to design everything all at > once first before getting to implement anything. Please, start with explaining what, in your opinion, a mount namespace _is_, and where does "mount X is attached at path P relative to mount Y" belong. What's the fundamental difference between CWD and any open descriptor for a directory? Why does it make sense to ban the former, but allow the equivalents done via the latter?