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

-- 
2.51.0

> Some mount attributes (traditionally associated with mount(8)-style options) have a sibling mount attribute with superficially similar user-facing behaviour

"Some mount attributes... have a sibling mount attribute"

Something is wrong here.

-- 
Askar Safin

Hi Aleksa,

On Fri, Sep 19, 2025 at 11:59:51AM +1000, Aleksa Sarai 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@cyphar.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

As said in another page, this should be

	.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
> +.BR fsconfig (2).
> +.\"

LGTM.

I've finished with the review of the patch set.  It's quite good.  :)


Have a lovely day!
Alex

>  .SS Extensibility
>  In order to allow for future extensibility,
>  .BR mount_setattr ()
> 
> -- 
> 2.51.0
> 
> 

-- 
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).

On 2025-09-19, Aleksa Sarai <cyphar@cyphar.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@cyphar.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/