[RFC PATCH 5/5] staging: vt6655: implement allocation failure handling

[Nam Cao <namcaov@gmail.com>]

The function device_rx_srv does not handle allocation failure very well.
Currently, it performs these steps:
        - Unmap DMA buffer and hand over the buffer to mac80211
        - Allocate and dma-map new buffer
        - If allocation fails, abort

The problem is that, it aborts while still marking the buffer as
OWNED_BY_HOST. So when this function is called again in the future, it
incorrectly perceives the same buffer as valid and dma-unmap and hand
over this buffer to mac80211 again.

Re-implement this function to do things in a different order:
        - Allocate and dma-map new buffer
        - If allocation fails, abort and give up the ownership of the
          buffer (so that the device can re-use this buffer)
        - If allocation does not fail: unmap dma buffer and hand over
          the buffer to mac80211

Thus, when the driver cannot allocate new buffer, it simply discards the
received data and re-use the current buffer.

Signed-off-by: Nam Cao <namcaov@gmail.com>
---
 drivers/staging/vt6655/device_main.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/vt6655/device_main.c b/drivers/staging/vt6655/device_main.c
index ca6c4266f010..8ae4ecca2ee3 100644
--- a/drivers/staging/vt6655/device_main.c
+++ b/drivers/staging/vt6655/device_main.c
@@ -826,6 +826,7 @@ static void device_free_td1_ring(struct vnt_private *priv)
 static int device_rx_srv(struct vnt_private *priv, unsigned int idx)
 {
 	struct vnt_rx_desc *rd;
+	struct vnt_rd_info new_info;
 	int works = 0;
 
 	for (rd = priv->pCurrRD[idx];
@@ -837,16 +838,18 @@ static int device_rx_srv(struct vnt_private *priv, unsigned int idx)
 		if (!rd->rd_info->skb)
 			break;
 
-		vnt_receive_frame(priv, rd);
-
-		if (!device_alloc_rx_buf(priv, rd->rd_info)) {
+		if (!device_alloc_rx_buf(priv, &new_info)) {
 			dev_err(&priv->pcid->dev,
 				"can not allocate rx buf\n");
+			rd->rd0.owner = OWNED_BY_NIC;
 			break;
-		} else {
-			device_init_rx_desc(priv, rd);
 		}
 
+		vnt_receive_frame(priv, rd);
+
+		memcpy(rd->rd_info, &new_info, sizeof(new_info));
+		device_init_rx_desc(priv, rd);
+
 		rd->rd0.owner = OWNED_BY_NIC;
 	}
 
-- 
2.25.1