From 63b0b1a34115e3ac4981d93451302f11ca45c96c Mon Sep 17 00:00:00 2001
From: Michael Kerrisk <mtk.manpages@gmail.com>
Date: Mon, 20 Aug 2018 16:24:20 +0200
Subject: [PATCH] mount.2: Clearly distinguish per-mount-point vs
 per-superblock mount flags

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
---
 man2/mount.2 | 41 +++++++++++++++++++++++++++++++++--------
 1 file changed, 33 insertions(+), 8 deletions(-)

diff --git a/man2/mount.2 b/man2/mount.2
index c6560065e..daaf158e1 100644
--- a/man2/mount.2
+++ b/man2/mount.2
@@ -281,21 +281,46 @@ flag to
 .BR open (2)
 was specified for all file opens to this filesystem).
 .PP
-From Linux 2.4 onward, the
+From Linux 2.4 onward, some of the above flags are
+settable on a per-mount basis,
+while others apply to the superblock of the mounted filesystem,
+meaning that all mounts of the same filesystem share those flags.
+(Previously, all of the flags were per-superblock.)
+.PP
+The per-mount-point flags are as follows:
+.IP * 3
+Since Linux 2.4:
 .BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID
 flags are settable on a per-mount-point basis.
-From kernel 2.6.16 onward,
+.IP *
+Since Linux 2.6.16:
 .B MS_NOATIME
 and
-.B MS_NODIRATIME
-are also settable on a per-mount-point basis.
-The
-.B MS_RELATIME
-flag is also settable on a per-mount-point basis.
+.BR MS_NODIRATIME .
+.IP *
+Since Linux 2.6.20:
+.BR MS_RELATIME .
+.PP
+The following flags are per-superblock:
+.BR MS_DIRSYNC ,
+.BR MS_LAZYTIME ,
+.BR MS_MANDLOCK ,
+.BR MS_MS_SILENT ,
+and
+.BR MS_SYNCHRONOUS .
+.\" And MS_I_VERSION?
+The inital settings of these flags are determined on the first
+mount of the filesystem, and will be shared by all subsequent mounts
+of the same filesystem.
+Subsequently, the settings of the flags can be changed
+via a remount operation (see below).
+Such changes will be visible via all mount points associated
+with the filesystem.
+.PP
 Since Linux 2.6.16,
 .B MS_RDONLY
 can be set or cleared on a per-mount-point basis as well as on
-the underlying filesystem.
+the underlying filesystem superblock.
 The mounted filesystem will be writable only if neither the filesystem
 nor the mountpoint are flagged as read-only.
 .\"