virtio-blk: Convert VirtIOBlockReq.out to structrue

The virtio code currently assumes that the outhdr is in its own iovec.
This is not guaranteed by the spec, so we should relax this assumption.

Convert the VirtIOBlockReq.out field to structrue so that we can use
iov_to_buf and then discard the header from the beginning of iovec.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 15 insertions, 7 deletions

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index b5cc3855cf..05610959a6 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -12,6 +12,7 @@
  */
 
 #include "qemu-common.h"
+#include "qemu/iov.h"
 #include "qemu/error-report.h"
 #include "trace.h"
 #include "hw/block/block.h"
@@ -81,7 +82,7 @@ static void virtio_blk_rw_complete(void *opaque, int ret)
     trace_virtio_blk_rw_complete(req, ret);
 
     if (ret) {
-        bool is_read = !(ldl_p(&req->out->type) & VIRTIO_BLK_T_OUT);
+        bool is_read = !(ldl_p(&req->out.type) & VIRTIO_BLK_T_OUT);
         if (virtio_blk_handle_rw_error(req, -ret, is_read))
             return;
     }
@@ -287,7 +288,7 @@ static void virtio_blk_handle_write(VirtIOBlockReq *req, MultiReqBuffer *mrb)
     BlockRequest *blkreq;
     uint64_t sector;
 
-    sector = ldq_p(&req->out->sector);
+    sector = ldq_p(&req->out.sector);
 
     bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_WRITE);
 
@@ -321,7 +322,7 @@ static void virtio_blk_handle_read(VirtIOBlockReq *req)
 {
     uint64_t sector;
 
-    sector = ldq_p(&req->out->sector);
+    sector = ldq_p(&req->out.sector);
 
     bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_READ);
 
@@ -344,22 +345,29 @@ static void virtio_blk_handle_request(VirtIOBlockReq *req,
     MultiReqBuffer *mrb)
 {
     uint32_t type;
+    struct iovec *iov = req->elem->out_sg;
+    unsigned out_num = req->elem->out_num;
 
     if (req->elem->out_num < 1 || req->elem->in_num < 1) {
         error_report("virtio-blk missing headers");
         exit(1);
     }
 
-    if (req->elem->out_sg[0].iov_len < sizeof(*req->out) ||
+    if (req->elem->out_sg[0].iov_len < sizeof(req->out) ||
         req->elem->in_sg[req->elem->in_num - 1].iov_len < sizeof(*req->in)) {
         error_report("virtio-blk header not in correct element");
         exit(1);
     }
 
-    req->out = (void *)req->elem->out_sg[0].iov_base;
+    if (unlikely(iov_to_buf(iov, out_num, 0, &req->out,
+                            sizeof(req->out)) != sizeof(req->out))) {
+        error_report("virtio-blk request outhdr too short");
+        exit(1);
+    }
+    iov_discard_front(&iov, &out_num, sizeof(req->out));
     req->in = (void *)req->elem->in_sg[req->elem->in_num - 1].iov_base;
 
-    type = ldl_p(&req->out->type);
+    type = ldl_p(&req->out.type);
 
     if (type & VIRTIO_BLK_T_FLUSH) {
         virtio_blk_handle_flush(req, mrb);
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index b495e42d6d..2571e961ec 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -138,7 +138,7 @@ typedef struct VirtIOBlockReq {
     VirtIOBlock *dev;
     VirtQueueElement *elem;
     struct virtio_blk_inhdr *in;
-    struct virtio_blk_outhdr *out;
+    struct virtio_blk_outhdr out;
     QEMUIOVector qiov;
     struct VirtIOBlockReq *next;
     BlockAcctCookie acct;