[Xen-changelog] Prevent an oops in Dom0 that occurs when a CD device, specified as one

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

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID df1521633fb519727adb80f15ea1f2e5b69dc3df
# Parent  c5551469f00e7e4dd79fe81d544c551f256da94b
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().

Based on a patch from Ross Maxfield at Novell.

Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
---
 linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff -r c5551469f00e -r df1521633fb5 
linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c    Tue May 16 09:21:33 
2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c    Tue May 16 09:40:38 
2006 +0100
@@ -55,6 +55,7 @@ int vbd_create(blkif_t *blkif, blkif_vde
               unsigned minor, int readonly)
 {
        struct vbd *vbd;
+       struct block_device *bdev;
 
        vbd = &blkif->vbd;
        vbd->handle   = handle; 
@@ -63,14 +64,16 @@ int vbd_create(blkif_t *blkif, blkif_vde
 
        vbd->pdevice  = MKDEV(major, minor);
 
-       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",
+       bdev = open_by_devnum(vbd->pdevice,
+                             vbd->readonly ? FMODE_READ : FMODE_WRITE);
+
+       if (IS_ERR(bdev)) {
+               DPRINTK("vbd_creat: device %08x could not be opened.\n",
                        vbd->pdevice);
                return -ENOENT;
        }
+
+       vbd->bdev = bdev;
 
        if (vbd->bdev->bd_disk == NULL) {
                DPRINTK("vbd_creat: device %08x doesn't exist.\n",

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