[PATCH] opps in blockback when missing media

["Ross Maxfield" <rmaxfiel@novell.com>]

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Hello,
I've created a patch to prevent an oops in Dom0 that occurs when a CD
device, specified as one of the 'hardrives' in the 'disk=' line of a
para-virtualized guest's def file, has no media when the guest is
started.

The oops occurs in vbd.c when vbd_size() is called from connect() (in
xenbus.c) and the vbd pointer is really an error code that comes from
the failed open that occurred in vbd_create().

This patch applies to changeset 9993

signed off by Ross Maxfield <rmaxfiel@novell.com>

--- a/linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c    Mon May 15
16:32:09 2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c    Mon May 15
11:49:39 2006 -0600
@@ -66,9 +66,10 @@ int vbd_create(blkif_t *blkif, blkif_vde
        vbd->bdev = open_by_devnum(
                vbd->pdevice,
                vbd->readonly ? FMODE_READ : FMODE_WRITE);
+
        if (IS_ERR(vbd->bdev)) {
-               DPRINTK("vbd_creat: device %08x doesn't exist.\n",
-                       vbd->pdevice);
+               DPRINTK("vbd_creat: device %08x could not be
opened.\n",
+               vbd->bdev = NULL;
                return -ENOENT;
        }

diff -r dc213d745642 linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c Mon May 15
16:32:09 2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c Mon May 15
11:49:39 2006 -0600
@@ -305,6 +305,9 @@ static void connect(struct backend_info

        DPRINTK("%s", dev->otherend);

+        if (be->blkif->vbd.bdev == NULL)
+               return;
+
        /* Supply the information about the device the frontend needs
*/
 again:
        err = xenbus_transaction_start(&xbt);


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diff -r dc213d745642 linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c	Mon May 15 16:32:09 2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c	Mon May 15 11:49:39 2006 -0600
@@ -66,9 +66,10 @@ int vbd_create(blkif_t *blkif, blkif_vde
 	vbd->bdev = open_by_devnum(
 		vbd->pdevice,
 		vbd->readonly ? FMODE_READ : FMODE_WRITE);
+
 	if (IS_ERR(vbd->bdev)) {
-		DPRINTK("vbd_creat: device %08x doesn't exist.\n",
-			vbd->pdevice);
+		DPRINTK("vbd_creat: device %08x could not be opened.\n",
+		vbd->bdev = NULL;
 		return -ENOENT;
 	}
 
diff -r dc213d745642 linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c	Mon May 15 16:32:09 2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c	Mon May 15 11:49:39 2006 -0600
@@ -305,6 +305,9 @@ static void connect(struct backend_info 
 
 	DPRINTK("%s", dev->otherend);
 
+        if (be->blkif->vbd.bdev == NULL)
+               return;
+
 	/* Supply the information about the device the frontend needs */
 again:
 	err = xenbus_transaction_start(&xbt);

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