Index: linux-2.6.27.21-0.1/block/blk-core.c
===================================================================
--- linux-2.6.27.21-0.1.orig/block/blk-core.c	2009-04-23 02:12:51.000000000 -0600
+++ linux-2.6.27.21-0.1/block/blk-core.c	2009-05-22 08:38:02.000000000 -0600
@@ -1335,6 +1335,8 @@
 
 #endif /* CONFIG_FAIL_MAKE_REQUEST */
 
+int dev_check_rdonly(struct block_device *bdev);
+
 /*
  * Check whether this bio extends beyond the end of the device.
  */
@@ -1436,6 +1438,12 @@
 
 		if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
 			goto end_io;

+               /* this is cfs's dev_rdonly check */
+               if (bio_rw(bio) == WRITE && dev_check_rdonly(bio->bi_bdev)) {
+                       bio_endio(bio, bio->bi_size, 0);
+                       break;
+               }
+
 		if (should_fail_request(bio))
 			goto end_io;
@@ -2189,6 +2197,91 @@
 }
 EXPORT_SYMBOL(kblockd_flush_work);
 
+ /*
+ * 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);
 int __init blk_dev_init(void)
 {
 	kblockd_workqueue = create_workqueue("kblockd");
Index: linux-2.6.27.21-0.1/fs/block_dev.c
===================================================================
--- linux-2.6.27.21-0.1.orig/fs/block_dev.c	2009-04-23 02:12:56.000000000 -0600
+++ linux-2.6.27.21-0.1/fs/block_dev.c	2009-05-22 08:38:02.000000000 -0600
@@ -1208,6 +1208,7 @@
 		if (bdev != bdev->bd_contains)
 			victim = bdev->bd_contains;
 		bdev->bd_contains = NULL;
+		dev_clear_rdonly(bdev);
 	}
 	unlock_kernel();
 	mutex_unlock(&bdev->bd_mutex);
Index: linux-2.6.27.21-0.1/include/linux/fs.h
===================================================================
--- linux-2.6.27.21-0.1.orig/include/linux/fs.h	2009-05-22 08:38:00.000000000 -0600
+++ linux-2.6.27.21-0.1/include/linux/fs.h	2009-05-22 08:38:02.000000000 -0600
@@ -1898,6 +1898,10 @@
 extern void submit_bio(int, struct bio *);
 extern int bdev_read_only(struct block_device *);
 #endif
+#define HAVE_CLEAR_RDONLY_ON_PUT
+extern void dev_set_rdonly(struct block_device *bdev);
+extern int dev_check_rdonly(struct block_device *bdev);
+extern 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);