[RFC][PATCH 27/27] create and pass read-only mnt flag into do_loopback()

[Dave Hansen <haveblue@us.ibm.com>]

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

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

This patch introduces MNT_RDONLY and ensures that it is
checked before any users may obtain write permissions
for a file through any mount.


Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---

 lxc-dave/fs/file.c             |    1 +
 lxc-dave/fs/inode.c            |    2 +-
 lxc-dave/fs/namespace.c        |    8 ++++++--
 lxc-dave/include/linux/mount.h |    3 +++
 lxc-dave/mm/filemap.c          |    3 +++
 5 files changed, 14 insertions(+), 3 deletions(-)

diff -puN fs/file.c~D8-actually-add-flags fs/file.c
--- lxc/fs/file.c~D8-actually-add-flags	2006-06-07 16:53:29.000000000 -0700
+++ lxc-dave/fs/file.c	2006-06-07 16:53:29.000000000 -0700
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/file.h>
+#include <linux/mount.h>
 #include <linux/bitops.h>
 #include <linux/interrupt.h>
 #include <linux/spinlock.h>
diff -puN fs/inode.c~D8-actually-add-flags fs/inode.c
--- lxc/fs/inode.c~D8-actually-add-flags	2006-06-07 16:53:29.000000000 -0700
+++ lxc-dave/fs/inode.c	2006-06-07 16:53:29.000000000 -0700
@@ -1185,7 +1185,7 @@ void touch_atime(struct vfsmount *mnt, s
 	struct inode *inode = dentry->d_inode;
 	struct timespec now;
 
-	if (IS_RDONLY(inode))
+	if (IS_RDONLY(inode) || (mnt->mnt_flags & MNT_RDONLY))
 		return;
 
 	if ((inode->i_flags & S_NOATIME) ||
diff -puN fs/namespace.c~D8-actually-add-flags fs/namespace.c
--- lxc/fs/namespace.c~D8-actually-add-flags	2006-06-07 16:53:29.000000000 -0700
+++ lxc-dave/fs/namespace.c	2006-06-07 16:53:29.000000000 -0700
@@ -905,7 +905,8 @@ static int do_change_type(struct nameida
 /*
  * do loopback mount.
  */
-static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
+static int do_loopback(struct nameidata *nd, char *old_name,
+		       int recurse, int mnt_flags)
 {
 	struct nameidata old_nd;
 	struct vfsmount *mnt = NULL;
@@ -943,6 +944,7 @@ static int do_loopback(struct nameidata 
 		spin_unlock(&vfsmount_lock);
 		release_mounts(&umount_list);
 	}
+	mnt->mnt_flags = mnt_flags;
 
 out:
 	up_write(&namespace_sem);
@@ -1403,6 +1405,8 @@ long do_mount(char *dev_name, char *dir_
 		((char *)data_page)[PAGE_SIZE - 1] = 0;
 
 	/* Separate the per-mountpoint flags */
+	if (flags & MS_RDONLY)
+		mnt_flags |= MNT_RDONLY;
 	if (flags & MS_NOSUID)
 		mnt_flags |= MNT_NOSUID;
 	if (flags & MS_NODEV)
@@ -1430,7 +1434,7 @@ long do_mount(char *dev_name, char *dir_
 		retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
 				    data_page);
 	else if (flags & MS_BIND)
-		retval = do_loopback(&nd, dev_name, flags & MS_REC);
+		retval = do_loopback(&nd, dev_name, flags & MS_REC, mnt_flags);
 	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
 		retval = do_change_type(&nd, flags);
 	else if (flags & MS_MOVE)
diff -puN include/linux/mount.h~D8-actually-add-flags include/linux/mount.h
--- lxc/include/linux/mount.h~D8-actually-add-flags	2006-06-07 16:53:29.000000000 -0700
+++ lxc-dave/include/linux/mount.h	2006-06-07 16:53:29.000000000 -0700
@@ -24,6 +24,7 @@
 #define MNT_NOEXEC	0x04
 #define MNT_NOATIME	0x08
 #define MNT_NODIRATIME	0x10
+#define MNT_RDONLY	0x20
 
 #define MNT_SHRINKABLE	0x100
 
@@ -63,6 +64,8 @@ static inline struct vfsmount *mntget(st
 
 static inline int mnt_want_write(struct vfsmount *mnt)
 {
+	if (mnt->mnt_flags & MNT_RDONLY)
+		return -EROFS;
 	atomic_inc(&mnt->mnt_writers);
 	return 0;
 }
diff -puN mm/filemap.c~D8-actually-add-flags mm/filemap.c
--- lxc/mm/filemap.c~D8-actually-add-flags	2006-06-07 16:53:29.000000000 -0700
+++ lxc-dave/mm/filemap.c	2006-06-07 16:53:29.000000000 -0700
@@ -23,6 +23,7 @@
 #include <linux/mman.h>
 #include <linux/pagemap.h>
 #include <linux/file.h>
+#include <linux/mount.h>
 #include <linux/uio.h>
 #include <linux/hash.h>
 #include <linux/writeback.h>
@@ -1960,6 +1961,8 @@ inline int generic_write_checks(struct f
                 return -EINVAL;
 
 	if (!isblk) {
+		if (file->f_vfsmnt->mnt_flags & MNT_RDONLY)
+			return -EROFS;
 		/* FIXME: this is for backwards compatibility with 2.4 */
 		if (file->f_flags & O_APPEND)
                         *pos = i_size_read(inode);
_