[Qemu-devel] [PATCH 01/10] virtio: move VirtQueueElement at the beginning of the structs

[Paolo Bonzini <pbonzini@redhat.com>]

The next patch will make virtqueue_pop/vring_pop allocate memory for a
"subclass" of VirtQueueElement.  For this to work, VirtQueueElement
must be the first field in the containing struct.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/scsi/virtio-scsi.c           |  3 +--
 include/hw/virtio/virtio-blk.h  |  2 +-
 include/hw/virtio/virtio-scsi.h | 13 ++++++-------
 3 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 3a4f520..1567da8 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -44,8 +44,7 @@ VirtIOSCSIReq *virtio_scsi_init_req(VirtIOSCSI *s, VirtQueue *vq)
 {
     VirtIOSCSIReq *req;
     VirtIOSCSICommon *vs = (VirtIOSCSICommon *)s;
-    const size_t zero_skip = offsetof(VirtIOSCSIReq, elem)
-                             + sizeof(VirtQueueElement);
+    const size_t zero_skip = offsetof(VirtIOSCSIReq, vring);
 
     req = g_malloc(sizeof(*req) + vs->cdb_size);
     req->vq = vq;
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index ae11a63..403ab86 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -60,9 +60,9 @@ typedef struct VirtIOBlock {
 } VirtIOBlock;
 
 typedef struct VirtIOBlockReq {
+    VirtQueueElement elem;
     int64_t sector_num;
     VirtIOBlock *dev;
-    VirtQueueElement elem;
     struct virtio_blk_inhdr *in;
     struct virtio_blk_outhdr out;
     QEMUIOVector qiov;
diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
index 088fe9f..63f5b51 100644
--- a/include/hw/virtio/virtio-scsi.h
+++ b/include/hw/virtio/virtio-scsi.h
@@ -102,18 +102,17 @@ typedef struct VirtIOSCSI {
 } VirtIOSCSI;
 
 typedef struct VirtIOSCSIReq {
+    /* Note:
+     * - fields up to resp_iov are initialized by virtio_scsi_init_req;
+     * - fields starting at vring are zeroed by virtio_scsi_init_req.
+     * */
+    VirtQueueElement elem;
+
     VirtIOSCSI *dev;
     VirtQueue *vq;
     QEMUSGList qsgl;
     QEMUIOVector resp_iov;
 
-    /* Note:
-     * - fields before elem are initialized by virtio_scsi_init_req;
-     * - elem is uninitialized at the time of allocation.
-     * - fields after elem are zeroed by virtio_scsi_init_req.
-     * */
-
-    VirtQueueElement elem;
     /* Set by dataplane code. */
     VirtIOSCSIVring *vring;
 
-- 
2.5.0