This commit structure the indirect desc table.
Then we can get the desc num directly when doing unmap.

And save the dma info to the struct, then the indirect
will not use the dma fields of the desc_extra. The subsequent
commits will make the dma fields are optional. But for
the indirect case, we must record the dma info.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 66 +++++++++++++++++++++---------------
 1 file changed, 38 insertions(+), 28 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 0dfbd17e5a87..22a588bba166 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c

@@ -72,9 +72,16 @@ struct vring_desc_state_split {
        struct vring_desc *indir_desc;  /* Indirect descriptor, if any. */
 };

+struct vring_packed_desc_indir {
+       dma_addr_t addr;                /* Descriptor Array DMA addr. */
+       u32 len;                        /* Descriptor Array length. */
+       u32 num;
+       struct vring_packed_desc desc[];
+};
+
 struct vring_desc_state_packed {
        void *data;                     /* Data for callback. */
-       struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
+       struct vring_packed_desc_indir *indir_desc; /* Indirect descriptor, if any. */