[PATCH 1/2] xen/blkback: Copy id field when doing BLKIF_DISCARD.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

We weren't copying the id field so when we sent the response
back to the frontend (especially with a 64-bit host and 32-bit
guest), we ended up using a random value. This lead to the
frontend crashing as it would try to pass to __blk_end_request_all
a NULL 'struct request' (b/c it would use the 'id' to find the
proper 'struct request' in its shadow array) and end up crashing:

BUG: unable to handle kernel NULL pointer dereference at 000000e4
IP: [<c0646d4c>] __blk_end_request_all+0xc/0x40
.. snip..
EIP is at __blk_end_request_all+0xc/0x40
.. snip..
 [<ed95db72>] blkif_interrupt+0x172/0x330 [xen_blkfront]

This fixes the bug by passing in the proper id for the response.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=824641
CC: stable@kernel.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 drivers/block/xen-blkback/common.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index 773cf27..9ad3b5e 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -257,6 +257,7 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst,
 		break;
 	case BLKIF_OP_DISCARD:
 		dst->u.discard.flag = src->u.discard.flag;
+		dst->u.discard.id = src->u.discard.id;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
@@ -287,6 +288,7 @@ static inline void blkif_get_x86_64_req(struct blkif_request *dst,
 		break;
 	case BLKIF_OP_DISCARD:
 		dst->u.discard.flag = src->u.discard.flag;
+		dst->u.discard.id = src->u.discard.id;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
-- 
1.7.7.6