mount.2: Clarify use of 'mountflags' and 'data' for MS_REMOUNT

Quoting Eric Biederman:

One thing that has come up recently (in 3 separate
implementations) is that mount(MS_REMOUNT|...,...) must include
all of the mount flags that need to be preserved.   People
creating read-only bind mounts tend to miss that and the locked
flags in mount namespaces.  That issue was flushed out now that
the kernel is now not allowing most mount flags to be cleared in
mount namespaces.  The interface is non-intuitive and we should
at least document the weirdness.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man2/mount.2 b/man2/mount.2
index 84efdae3c0a1d686509e0d21d32da0f87478ef26..bf341aa75f14a1f040b4ed62020e1f6411ea9fa5 100644 (file)
--- a/man2/mount.2
+++ b/man2/mount.2
@@ -241,6 +241,13 @@ call;
 and
 .I filesystemtype
 are ignored.
+The
+.I mountflags
+and
+.I data
+arguments should match the values used in the original
+.BR mount ()
+call, except for those parameters that are being deliberately changed.
 
 The following
 .I mountflags