Added a count of the number of users of this block device, and refuse to close

down the frontend until that number becomes 0.  There are no reasonable
semantics for hot-unplugging a block device beneath a mounted filesystem, and
this solution ensures that the guest is not crashed nor the filesystem corruptedby the actions of the administrator.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

diff --git a/linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c b/linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c
index cab043c15cbe642bcfa7caeaf487263140be37a4..f204629f4d406814edb2c2ab40707432ade8b8da 100644 (file)
--- a/linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c
+++ b/linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c
@@ -117,6 +117,8 @@ static int blkfront_probe(struct xenbus_device *dev,
                info->shadow[i].req.id = i+1;
        info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;
 
+       info->users = 0;
+
        /* Front end dir is a number, which is used as the id. */
        info->handle = simple_strtoul(strrchr(dev->nodename,'/')+1, NULL, 0);
        dev->data = info;
@@ -265,6 +267,7 @@ static void backend_changed(struct xenbus_device *dev,
                            XenbusState backend_state)
 {
        struct blkfront_info *info = dev->data;
+       struct block_device *bd;
 
        DPRINTK("blkfront:backend_changed.\n");
 
@@ -281,7 +284,18 @@ static void backend_changed(struct xenbus_device *dev,
                break;
 
        case XenbusStateClosing:
-               blkfront_closing(dev);
+               bd = bdget(info->dev);
+               if (bd == NULL)
+                       xenbus_dev_fatal(dev, -ENODEV, "bdget failed");
+
+               down(&bd->bd_sem);
+               if (info->users > 0)
+                       xenbus_dev_error(dev, -EBUSY,
+                                        "Device in use; refusing to close");
+               else
+                       blkfront_closing(dev);
+               up(&bd->bd_sem);
+               bdput(bd);
                break;
        }
 }
@@ -414,12 +428,26 @@ static void blkif_restart_queue_callback(void *arg)
 
 int blkif_open(struct inode *inode, struct file *filep)
 {
+       struct blkfront_info *info = inode->i_bdev->bd_disk->private_data;
+       info->users++;
        return 0;
 }
 
 
 int blkif_release(struct inode *inode, struct file *filep)
 {
+       struct blkfront_info *info = inode->i_bdev->bd_disk->private_data;
+       info->users--;
+       if (info->users == 0) {
+               /* Check whether we have been instructed to close.  We will
+                  have ignored this request initially, as the device was
+                  still mounted. */
+               struct xenbus_device * dev = info->xbdev;
+               XenbusState state = xenbus_read_driver_state(dev->otherend);
+
+               if (state == XenbusStateClosing)
+                       blkfront_closing(dev);
+       }
        return 0;
 }
 

diff --git a/linux-2.6-xen-sparse/drivers/xen/blkfront/block.h b/linux-2.6-xen-sparse/drivers/xen/blkfront/block.h
index 35f14403880a7930faeef20cf9f60c5f31b5d2a1..809451aec7359eb8344650781bd4b7fd69b4d92b 100644 (file)
--- a/linux-2.6-xen-sparse/drivers/xen/blkfront/block.h
+++ b/linux-2.6-xen-sparse/drivers/xen/blkfront/block.h
@@ -127,6 +127,12 @@ struct blkfront_info
        struct gnttab_free_callback callback;
        struct blk_shadow shadow[BLK_RING_SIZE];
        unsigned long shadow_free;
+
+       /**
+        * The number of people holding this device open.  We won't allow a
+        * hot-unplug unless this is 0.
+        */
+       int users;
 };
 
 extern spinlock_t blkif_io_lock;