MS_REMOUNT|MS_BIND affect all per-mount-point flag. MS_READONLY is only special because it, uniquely, is both a per-mount-point flag *and* a per-filesystem flag.
So the sections of per-mount-point flags and MS_REMOUNT can usefully be clarified. Signed-off-by: NeilBrown <ne...@suse.com> --- man2/mount.2 | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/man2/mount.2 b/man2/mount.2 index 35fdda084d61..3e5348368757 100644 --- a/man2/mount.2 +++ b/man2/mount.2 @@ -288,6 +288,12 @@ are also settable on a per-mount-point basis. The .B MS_RELATIME flag is also settable on a per-mount-point basis. +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 mounted filesystem will only be +writable if neither the filesystem nor the mountpoint are flagged as +read-only. .\" .SS Remounting an existing mount An existing mount may be remounted by specifying @@ -317,6 +323,10 @@ and arguments should match the values used in the original .BR mount () call, except for those parameters that are being deliberately changed. +Another exception is that +.B MS_BIND +has a different meaning for remount, and it should only be included if +explicitly desired. The following .I mountflags @@ -351,17 +361,20 @@ then the remount operation preserves the existing values of these flags (rather than defaulting to .BR MS_RELATIME ). -Since Linux 2.6.26, this flag can also be used to make +Since Linux 2.6.26, this flag can be used with +.B MS_BIND +to only modify the per-mount-point flags. .\" See https://lwn.net/Articles/281157/ -an existing bind mount read-only by specifying +This is particularly useful for setting or clearing the "read-only" +flag on a mount point without changing the underlying filesystem. +Specifying .IR mountflags as: MS_REMOUNT | MS_BIND | MS_RDONLY -Note that only the -.BR MS_RDONLY -setting of the bind mount can be changed in this manner. +will make access through this mountpoint read-only, without affecting +other mount points. .\" .SS Creating a bind mount If -- 2.12.2
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