With MS_REMOUNT, it is difficult to change mount flags individually,
without touching other mount flags or options, having to parse
/proc/mounts to get the old flag values and options.

It is also difficult to change a mount flag recursively, having to
walk the mount tree in userspace.

This patch solves this problem by generalizing do_change_type() so
that not only the propagation property can be changed, but mnt_flags
can be set/cleared individually.

From: Miklos Szeredi <mszeredi@suse.cz>

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2007-04-13 13:04:04.000000000 +0200
+++ linux/fs/namespace.c	2007-04-13 13:04:29.000000000 +0200
@@ -955,19 +956,28 @@ out_unlock:
 /*
  * recursively change the type of the mountpoint.
  */
-static int do_change_type(struct nameidata *nd, int flag)
+static int do_change_mnt(struct nameidata *nd, int flag, int mnt_flags)
 {
 	struct vfsmount *m, *mnt = nd->mnt;
 	int recurse = flag & MS_REC;
-	int type = flag & ~MS_REC;
+	int type = flag & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE);
 
 	if (nd->dentry != nd->mnt->mnt_root)
 		return -EINVAL;
 
 	down_write(&namespace_sem);
 	spin_lock(&vfsmount_lock);
-	for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
-		change_mnt_propagation(m, type);
+	for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL)) {
+		if (type)
+			change_mnt_propagation(m, type);
+
+		if (flag & (MS_SETFLAGS | MS_CLEARFLAGS))
+			m->mnt_flags = mnt_flags;
+		else if (flag & MS_SETFLAGS)
+			m->mnt_flags |= mnt_flags;
+		else if (flag & MS_CLEARFLAGS)
+			m->mnt_flags &= ~mnt_flags;
+	}
 	spin_unlock(&vfsmount_lock);
 	up_write(&namespace_sem);
 	return 0;
@@ -1514,8 +1526,9 @@ long do_mount(char *dev_name, char *dir_
 				    data_page);
 	else if (flags & MS_BIND)
 		retval = do_loopback(&nd, dev_name, flags);
-	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
-		retval = do_change_type(&nd, flags);
+	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE |
+			  MS_SETFLAGS | MS_CLEARFLAGS))
+		retval = do_change_mnt(&nd, flags, mnt_flags);
 	else if (flags & MS_MOVE)
 		retval = do_move_mount(&nd, dev_name);
 	else
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2007-04-13 13:04:04.000000000 +0200
+++ linux/include/linux/fs.h	2007-04-13 13:04:29.000000000 +0200
@@ -127,6 +127,9 @@ extern int dir_notify_enable;
 #define MS_SHARED	(1<<20)	/* change to shared */
 #define MS_RELATIME	(1<<21)	/* Update atime relative to mtime/ctime. */
 #define MS_SETUSER	(1<<22) /* set mnt_uid to current user */
+#define MS_SETFLAGS	(1<<23) /* set specified mount flags */
+#define MS_CLEARFLAGS	(1<<24) /* clear specified mount flags */
+/* MS_SETFLAGS | MS_CLEARFLAGS: change mount flags to specified */
 #define MS_ACTIVE	(1<<30)
 #define MS_NOUSER	(1<<31)
 

--
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