[Xen-changelog] Added a count of the number of users of this block device, and refuse to close

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User emellor@xxxxxxxxxxxxxxxxxxxxxx
# Node ID d2b957902c6b48fb675ffbde5a46f6d8946c4372
# Parent  64d9190320012e88270a4bbbd418feecb81ede42
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@xxxxxxxxxxxxx>

diff -r 64d919032001 -r d2b957902c6b 
linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c
--- a/linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c      Thu Nov 24 
15:57:45 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c      Thu Nov 24 
19:53:09 2005
@@ -117,6 +117,8 @@
                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 @@
                            XenbusState backend_state)
 {
        struct blkfront_info *info = dev->data;
+       struct block_device *bd;
 
        DPRINTK("blkfront:backend_changed.\n");
 
@@ -281,7 +284,18 @@
                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 @@
 
 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 -r 64d919032001 -r d2b957902c6b 
linux-2.6-xen-sparse/drivers/xen/blkfront/block.h
--- a/linux-2.6-xen-sparse/drivers/xen/blkfront/block.h Thu Nov 24 15:57:45 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/blkfront/block.h Thu Nov 24 19:53:09 2005
@@ -127,6 +127,12 @@
        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;

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