linux-kernel - Re: [PATCH v4 10/10] man/man2/{fsconfig,mount_setattr}.2: add note about attribute-parameter distinction

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <2025-09-19-retro-married-traction-cinch-dgVzgj@cyphar.com>
Date: Fri, 19 Sep 2025 22:23:47 +1000
From: Aleksa Sarai <cyphar@...har.com>
To: Alejandro Colomar <alx@...nel.org>
Cc: "Michael T. Kerrisk" <mtk.manpages@...il.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, Askar Safin <safinaskar@...omail.com>, 
	"G. Branden Robinson" <g.branden.robinson@...il.com>, linux-man@...r.kernel.org, linux-api@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	David Howells <dhowells@...hat.com>, Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v4 10/10] man/man2/{fsconfig,mount_setattr}.2: add note
 about attribute-parameter distinction

On 2025-09-19, Aleksa Sarai <cyphar@...har.com> wrote:
> This was not particularly well documented in mount(8) nor mount(2), and
> since this is a fairly notable aspect of the new mount API, we should
> probably add some words about it.
> 
> Signed-off-by: Aleksa Sarai <cyphar@...har.com>
> ---
>  man/man2/fsconfig.2      | 12 ++++++++++++
>  man/man2/mount_setattr.2 | 40 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/man/man2/fsconfig.2 b/man/man2/fsconfig.2
> index 5a18e08c700ac93aa22c341b4134944ee3c38d0b..d827a7b96e08284fb025f94c3348a4acc4571b7d 100644
> --- a/man/man2/fsconfig.2
> +++ b/man/man2/fsconfig.2
> @@ -579,6 +579,18 @@ .SS Generic filesystem parameters
>  Linux Security Modules (LSMs)
>  are also generic with respect to the underlying filesystem.
>  See the documentation for the LSM you wish to configure for more details.
> +.SS Mount attributes and filesystem parameters
> +Some filesystem parameters
> +(traditionally associated with
> +.BR mount (8)-style
> +options)
> +have a sibling mount attribute
> +with superficially similar user-facing behaviour.
> +.P
> +For a description of the distinction between
> +mount attributes and filesystem parameters,
> +see the "Mount attributes and filesystem parameters" subsection of
> +.BR mount_setattr (2).
>  .SH CAVEATS
>  .SS Filesystem parameter types
>  As a result of
> diff --git a/man/man2/mount_setattr.2 b/man/man2/mount_setattr.2
> index b27db5b96665cfb0c387bf5b60776d45e0139956..f7d0b96fddf97698e36cab020f1d695783143025 100644
> --- a/man/man2/mount_setattr.2
> +++ b/man/man2/mount_setattr.2
> @@ -790,6 +790,46 @@ .SS ID-mapped mounts
>  .BR chown (2)
>  system call changes the ownership globally and permanently.
>  .\"
> +.SS Mount attributes and filesystem parameters
> +Some mount attributes
> +(traditionally associated with
> +.BR mount (8)-style
> +options)
> +have a sibling mount attribute
> +with superficially similar user-facing behaviour.
> +For example, the
> +.I -o ro
> +option to
> +.BR mount (8)
> +can refer to the
> +"read-only" filesystem parameter,
> +or the "read-only" mount attribute.
> +Both of these result in mount objects becoming read-only,
> +but they do have different behaviour.
> +.P
> +The distinction between these two kinds of option is that
> +mount object attributes are applied per-mount-object
> +(allowing different mount objects
> +derived from a given filesystem instance
> +to have different attributes),
> +while filesystem instance parameters
> +("superblock flags" in kernel-developer parlance)
> +apply to all mount objects
> +derived from the same filesystem instance.
> +.P
> +When using
> +.BR mount (2),
> +the line between these two types of mount options was blurred.
> +However, with
> +.BR mount_setattr ()
> +and
> +.BR fsconfig (2),
> +the distinction is made much clearer.
> +Mount attributes are configured with
> +.BR mount_setattr (),
> +while filesystem parameters can be configured using
                               are configured using

probably reads a bit better here. I'll include it in the next version if
this isn't merged, but I won't resend the whole patchset for a one-word
change.

> +.BR fsconfig (2).
> +.\"
>  .SS Extensibility
>  In order to allow for future extensibility,
>  .BR mount_setattr ()
> 
> -- 
> 2.51.0
> 

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

Download attachment "signature.asc" of type "application/pgp-signature" (266 bytes)