diff -rup linux-2.6.16.i686.orig/block/ll_rw_blk.c linux-2.6.16.i686/block/ll_rw_blk.c
--- linux-2.6.16.i686.orig/block/ll_rw_blk.c	2007-05-29 15:24:36.000000000 +0300
+++ linux-2.6.16.i686/block/ll_rw_blk.c	2007-05-29 15:33:50.000000000 +0300
@@ -2940,6 +2940,8 @@ static void handle_bad_sector(struct bio
 	set_bit(BIO_EOF, &bio->bi_flags);
 }
 
+int dev_check_rdonly(struct block_device *bdev);
+
 /**
  * generic_make_request: hand a buffer to its device driver for I/O
  * @bio:  The bio describing the location in memory and on the device.
@@ -3020,6 +3022,12 @@ end_io:
 
 		if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
 			goto end_io;
+		/* this is cfs's dev_rdonly check */
+		if (bio->bi_rw == WRITE &&
+				dev_check_rdonly(bio->bi_bdev)) {
+			bio_endio(bio, bio->bi_size, 0);
+			break;
+		}
 
 		/*
 		 * If this device has partitions, remap block n
@@ -3593,6 +3601,91 @@ void swap_io_context(struct io_context *
 	*ioc2 = temp;
 }
 EXPORT_SYMBOL(swap_io_context);
+ /*
+ * Debug code for turning block devices "read-only" (will discard writes
+ * silently).  This is for filesystem crash/recovery testing.
+ */
+struct deventry {
+	dev_t dev;
+	struct deventry *next;
+};
+
+static struct deventry *devlist = NULL;
+static spinlock_t devlock = SPIN_LOCK_UNLOCKED; 
+
+int dev_check_rdonly(struct block_device *bdev) 
+{
+	struct deventry *cur;
+	if (!bdev) return 0;
+	spin_lock(&devlock);
+	cur = devlist;
+	while(cur) {
+		if (bdev->bd_dev == cur->dev) {
+			spin_unlock(&devlock);
+			return 1;
+	}
+		cur = cur->next;
+	}
+	spin_unlock(&devlock);
+	return 0;
+}
+
+void dev_set_rdonly(struct block_device *bdev)
+{
+	struct deventry *newdev, *cur;
+
+	if (!bdev) 
+		return;
+	newdev = kmalloc(sizeof(struct deventry), GFP_KERNEL);
+	if (!newdev) 
+		return;
+	
+	spin_lock(&devlock);
+	cur = devlist;
+	while(cur) {
+		if (bdev->bd_dev == cur->dev) {
+			spin_unlock(&devlock);
+			kfree(newdev);
+			return;
+		}
+		cur = cur->next;
+	}
+	newdev->dev = bdev->bd_dev;
+	newdev->next = devlist;
+	devlist = newdev;
+	spin_unlock(&devlock);
+	printk(KERN_WARNING "Turning device %s (%#x) read-only\n",
+	       bdev->bd_disk ? bdev->bd_disk->disk_name : "", bdev->bd_dev);
+}
+
+void dev_clear_rdonly(struct block_device *bdev) 
+{
+	struct deventry *cur, *last = NULL;
+	if (!bdev) return;
+	spin_lock(&devlock);
+	cur = devlist;
+	while(cur) {
+		if (bdev->bd_dev == cur->dev) {
+			if (last) 
+				last->next = cur->next;
+			else
+				devlist = cur->next;
+			spin_unlock(&devlock);
+			kfree(cur);
+			printk(KERN_WARNING "Removing read-only on %s (%#x)\n",
+			       bdev->bd_disk ? bdev->bd_disk->disk_name :
+					       "unknown block", bdev->bd_dev);
+			return;
+		}
+		last = cur;
+		cur = cur->next;
+	}
+	spin_unlock(&devlock);
+}
+
+EXPORT_SYMBOL(dev_set_rdonly);
+EXPORT_SYMBOL(dev_clear_rdonly);
+EXPORT_SYMBOL(dev_check_rdonly);
 
 /*
  * sysfs parts below
diff -rup linux-2.6.16.i686.orig/fs/block_dev.c linux-2.6.16.i686/fs/block_dev.c
--- linux-2.6.16.i686.orig/fs/block_dev.c	2006-03-20 07:53:29.000000000 +0200
+++ linux-2.6.16.i686/fs/block_dev.c	2007-05-29 15:35:00.000000000 +0300
@@ -60,6 +60,7 @@ static void kill_bdev(struct block_devic
 {
 	invalidate_bdev(bdev, 1);
 	truncate_inode_pages(bdev->bd_inode->i_mapping, 0);
+	dev_clear_rdonly(bdev);
 }	
 
 int set_blocksize(struct block_device *bdev, int size)
diff -rup linux-2.6.16.i686.orig/include/linux/fs.h linux-2.6.16.i686/include/linux/fs.h
--- linux-2.6.16.i686.orig/include/linux/fs.h	2007-05-29 15:24:38.000000000 +0300
+++ linux-2.6.16.i686/include/linux/fs.h	2007-05-29 15:33:50.000000000 +0300
@@ -1541,6 +1541,10 @@ extern void file_kill(struct file *f);
 struct bio;
 extern void submit_bio(int, struct bio *);
 extern int bdev_read_only(struct block_device *);
+#define HAVE_CLEAR_RDONLY_ON_PUT
+void dev_set_rdonly(struct block_device *bdev);
+int dev_check_rdonly(struct block_device *bdev);
+void dev_clear_rdonly(struct block_device *bdev);
 extern int set_blocksize(struct block_device *, int);
 extern int sb_set_blocksize(struct super_block *, int);
 extern int sb_min_blocksize(struct super_block *, int);