linux-kernel - Re: [PATCH v3 06/12] man/man2/fsconfig.2: document "new" mount API

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Message-ID: <2025-08-21.1755776485-stony-another-giggle-rodent-9HLjPO@cyphar.com>
Date: Thu, 21 Aug 2025 21:44:42 +1000
From: Aleksa Sarai <cyphar@...har.com>
To: Askar Safin <safinaskar@...omail.com>
Cc: Alejandro Colomar <alx@...nel.org>, 
	"Michael T. Kerrisk" <mtk.manpages@...il.com>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Jan Kara <jack@...e.cz>, "G. Branden Robinson" <g.branden.robinson@...il.com>, 
	linux-man <linux-man@...r.kernel.org>, linux-api <linux-api@...r.kernel.org>, 
	linux-fsdevel <linux-fsdevel@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org>, 
	David Howells <dhowells@...hat.com>, Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v3 06/12] man/man2/fsconfig.2: document "new" mount API

On 2025-08-21, Askar Safin <safinaskar@...omail.com> wrote:
>  ---- On Tue, 12 Aug 2025 22:25:40 +0400  Aleksa Sarai <cyphar@...har.com> wrote --- 
>  > On 2025-08-09, Aleksa Sarai <cyphar@...har.com> wrote:
>  > > +Note that the Linux kernel reuses filesystem instances
>  > > +for many filesystems,
>  > > +so (depending on the filesystem being configured and parameters used)
>  > > +it is possible for the filesystem instance "created" by
>  > > +.B \%FSCONFIG_CMD_CREATE
>  > > +to, in fact, be a reference
>  > > +to an existing filesystem instance in the kernel.
>  > > +The kernel will attempt to merge the specified parameters
>  > > +of this filesystem configuration context
>  > > +with those of the filesystem instance being reused,
>  > > +but some parameters may be
>  > > +.IR "silently ignored" .
>  > 
>  > While looking at this again, I realised this explanation is almost
>  > certainly incorrect in a few places (and was based on a misunderstanding
>  > of how sget_fc() works and how it interacts with vfs_get_tree()).
>  > 
>  > I'll rewrite this in the next version.
> 
> This recent patch seems to be relevant:
> https://lore.kernel.org/all/20250816-debugfs-mount-opts-v3-1-d271dad57b5b@posteo.net/

I'm aware of that, I was in one of the previous threads. There are some
deeper consistency issues that I'm writing patches for at the moment.

I'm of two minds whether I should fix the behaviour and then re-send
man-pages with updated text (delaying the next round of man-page reviews
by a month) or just reduce the specificity of this text and then add
more details after it has been fixed.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/

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