From 4a92140584d2a52ab6c0d3a71975c8f235712c94 Mon Sep 17 00:00:00 2001
From: pooka <pooka@NetBSD.org>
Date: Thu, 13 Jan 2011 07:25:50 +0000
Subject: [PATCH] allow file system to decide if it can be downgraded from r/w
 to r/o

---
 sys/kern/vfs_syscalls.c | 7 ++++---
 sys/sys/fstypes.h       | 4 +++-
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 396b8c275300..7abe8c5c8a1d 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: vfs_syscalls.c,v 1.413 2011/01/02 05:12:33 dholland Exp $	*/
+/*	$NetBSD: vfs_syscalls.c,v 1.414 2011/01/13 07:25:50 pooka Exp $	*/
 
 /*-
  * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
@@ -66,7 +66,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_syscalls.c,v 1.413 2011/01/02 05:12:33 dholland Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_syscalls.c,v 1.414 2011/01/13 07:25:50 pooka Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_fileassoc.h"
@@ -169,7 +169,8 @@ mount_update(struct lwp *l, struct vnode *vp, const char *path, int flags,
 	 * prevent read-write to read-only downgrades.
 	 */
 	if ((flags & (MNT_RELOAD | MNT_RDONLY)) != 0 &&
-	    (mp->mnt_flag & MNT_RDONLY) == 0) {
+	    (mp->mnt_flag & MNT_RDONLY) == 0 &&
+	    (mp->mnt_iflag & IMNT_CAN_RWTORO) == 0) {
 		error = EOPNOTSUPP;	/* Needs translation */
 		goto out;
 	}
diff --git a/sys/sys/fstypes.h b/sys/sys/fstypes.h
index 7f9f6299eded..f8e540d8cb5e 100644
--- a/sys/sys/fstypes.h
+++ b/sys/sys/fstypes.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: fstypes.h,v 1.27 2011/01/13 07:23:39 pooka Exp $	*/
+/*	$NetBSD: fstypes.h,v 1.28 2011/01/13 07:25:50 pooka Exp $	*/
 
 /*
  * Copyright (c) 1989, 1991, 1993
@@ -210,6 +210,7 @@ typedef struct fhandle	fhandle_t;
 #define	IMNT_DTYPE	0x00000040	/* returns d_type fields */
 #define	IMNT_HAS_TRANS	0x00000080	/* supports transactions */
 #define	IMNT_MPSAFE	0x00000100	/* file system code MP safe */
+#define	IMNT_CAN_RWTORO	0x00000200	/* can downgrade fs to from rw to r/o */
 
 #define	__MNT_FLAGS \
 	__MNT_BASIC_FLAGS \
@@ -254,6 +255,7 @@ typedef struct fhandle	fhandle_t;
 
 #define	__IMNT_FLAG_BITS \
 	"\20" \
+	"\12IMNT_CAN_RWTORO" \
         "\11IMNT_MPSAFE" \
 	"\10IMNT_HAS_TRANS" \
 	"\07IMNT_DTYPE" \