After qemu_iovec_destroy, the QEMUIOVector's size is zeroed and
the zero size ultimately is used to compute virtqueue_push's len
argument. Therefore, reads from virtio-blk devices did not
migrate their results correctly. (Writes were okay).
Save the size in submit_requests, and use it when the request is
completed.
Based on a patch by Wen Congyang.
Signed-off-by: Wen Congyang <we...@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
hw/block/dataplane/virtio-blk.c | 2 +-
hw/block/virtio-blk.c | 16 +++++++++++++++-
include/hw/virtio/virtio-blk.h | 1 +
3 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index cd41478..b37ede3 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -78,7 +78,7 @@ static void complete_request_vring(VirtIOBlockReq *req,
unsigned char status)
stb_p(&req->in->status, status);
vring_push(s->vdev, &req->dev->dataplane->vring, &req->elem,
- req->qiov.size + sizeof(*req->in));
+ req->read_size + sizeof(*req->in));
/* Suppress notification to guest by BH and its scheduled
* flag because requests are completed as a batch after io
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 000c38d..2f00dc4 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -33,6 +33,7 @@ VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
VirtIOBlockReq *req = g_slice_new(VirtIOBlockReq);
req->dev = s;
req->qiov.size = 0;
+ req->read_size = 0;
req->next = NULL;
req->mr_next = NULL;
return req;
@@ -54,7 +55,7 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req,
trace_virtio_blk_req_complete(req, status);
stb_p(&req->in->status, status);
- virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in));
+ virtqueue_push(s->vq, &req->elem, req->read_size + sizeof(*req->in));
virtio_notify(vdev, s->vq);
}
@@ -102,6 +103,14 @@ static void virtio_blk_rw_complete(void *opaque, int ret)
if (ret) {
int p = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type);
bool is_read = !(p & VIRTIO_BLK_T_OUT);
+ /* Note that memory may be dirtied on read failure. If the
+ * virtio request is not completed here, as is the case for
+ * BLOCK_ERROR_ACTION_STOP, the memory may not be copied
+ * correctly during live migration. While this is ugly,
+ * it is acceptable because the device is free to write to
+ * the memory until the request is completed (which will
+ * happen on the other side of the migration).
+ */
if (virtio_blk_handle_rw_error(req, -ret, is_read)) {
continue;
}
@@ -348,9 +357,14 @@ static inline void submit_requests(BlockBackend *blk,
MultiReqBuffer *mrb,
}
if (is_write) {
+ mrb->reqs[start]->read_size = 0;
blk_aio_writev(blk, sector_num, qiov, nb_sectors,
virtio_blk_rw_complete, mrb->reqs[start]);
} else {
+ /* Save old qiov->size, which will be used in
+ * virtio_blk_complete_request()
+ */
+ mrb->reqs[start]->read_size = qiov->size;
blk_aio_readv(blk, sector_num, qiov, nb_sectors,
virtio_blk_rw_complete, mrb->reqs[start]);
}
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index b3ffcd9..d73ec06 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -67,6 +67,7 @@ typedef struct VirtIOBlockReq {
struct virtio_blk_inhdr *in;
struct virtio_blk_outhdr out;
QEMUIOVector qiov;
+ size_t read_size;
struct VirtIOBlockReq *next;
struct VirtIOBlockReq *mr_next;
BlockAcctCookie acct;
--
2.3.4
