[PATCH v3 12/12] man/man2/{fsconfig,mount_setattr}.2: add note about attribute-parameter distinction

[Aleksa Sarai <cyphar@cyphar.com>]

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      | 11 +++++++++++
 man/man2/mount_setattr.2 | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/man/man2/fsconfig.2 b/man/man2/fsconfig.2
index 97c9aff0e0c195e6028e1c7bd70e40905ba9f994..a7642e1633541bf8f5cd537db22987a4ec70da06 100644
--- a/man/man2/fsconfig.2
+++ b/man/man2/fsconfig.2
@@ -522,6 +522,17 @@ .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)
+are also mount attributes.
+.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 d98e7d70870c082144dfa47e31ddf091c8545e4f..2927b012eed1569e0d78a2fb91815f364fca124d 100644
--- a/man/man2/mount_setattr.2
+++ b/man/man2/mount_setattr.2
@@ -790,6 +790,43 @@ .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)
+are also filesystem parameters.
+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.
+.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 ()

-- 
2.50.1