[PATCH] r/o bind mounts: honor mount writer counts at remount

Originally from: Herbert Poetzl <herbert@13thfloor.at>

This is the core of the read-only bind mount patch set.

Note that this does _not_ add a "ro" option directly to the bind mount
operation.  If you require such a mount, you must first do the bind, then
follow it up with a 'mount -o remount,ro' operation:

If you wish to have a r/o bind mount of /foo on bar:

	mount --bind /foo /bar
	mount -o remount,ro /bar

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/mount.h b/include/linux/mount.h
index 8c8e94369ac8..d6600e3f7e45 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -29,6 +29,7 @@ struct mnt_namespace;
 #define MNT_NOATIME     0x08
 #define MNT_NODIRATIME  0x10
 #define MNT_RELATIME    0x20
+#define MNT_READONLY    0x40    /* does the user want this to be r/o? */
 
 #define MNT_SHRINKABLE  0x100
 #define MNT_IMBALANCED_WRITE_COUNT      0x200 /* just for debugging */