[PATCH] fix floppy.c to store correct ro/rw status in underlying gendisk

Evgeny Stambulchik found that doing the following always worked:

# mount /dev/fd0 /mnt/floppy/
mount: block device /dev/fd0 is write-protected, mounting read-only
# mount -o remount,rw /mnt/floppy
# echo $?
0

This is the case because the block device /dev/fd0 is writeable but the
floppy disk is marked protected.  A fix is to simply have floppy_open mark
the underlying gendisk policy according to reality (since the VFS doesn't
provide a way for do_remount_sb to inquire as to the current device
status).
Signed-off-by: Jon Masters <jcm@jonmasters.org>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/block/floppy.c

@@ -3714,6 +3714,12 @@ static int floppy_open(struct inode *inode, struct file *filp)
 		USETF(FD_VERIFY);
 	}
 
+	/* set underlying gendisk policy to reflect real ro/rw status */
+	if (UTESTF(FD_DISK_WRITABLE))
+		inode->i_bdev->bd_disk->policy = 0;
+	else
+		inode->i_bdev->bd_disk->policy = 1;
+
 	if (UDRS->fd_ref == -1 || (UDRS->fd_ref && (filp->f_flags & O_EXCL)))
 		goto out2;