[PATCH] HID: hyperv: Use in-place iterator API in the channel callback

[Dexuan Cui <decui@microsoft.com>]

Simplify the ring buffer handling with the in-place API.

Also avoid the dynamic allocation and the memory leak in the channel
callback function.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
---

Hi Jiri, Benjamin, can this patch go through Sasha's hyperv tree:
https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git

This is a purely Hyper-V specific change.

 drivers/hid/hid-hyperv.c | 56 +++++++++---------------------------------------
 1 file changed, 10 insertions(+), 46 deletions(-)

diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
index 7795831..f363163 100644
--- a/drivers/hid/hid-hyperv.c
+++ b/drivers/hid/hid-hyperv.c
@@ -314,60 +314,24 @@ static void mousevsc_on_receive(struct hv_device *device,
 
 static void mousevsc_on_channel_callback(void *context)
 {
-	const int packet_size = 0x100;
-	int ret;
 	struct hv_device *device = context;
-	u32 bytes_recvd;
-	u64 req_id;
 	struct vmpacket_descriptor *desc;
-	unsigned char	*buffer;
-	int	bufferlen = packet_size;
-
-	buffer = kmalloc(bufferlen, GFP_ATOMIC);
-	if (!buffer)
-		return;
-
-	do {
-		ret = vmbus_recvpacket_raw(device->channel, buffer,
-					bufferlen, &bytes_recvd, &req_id);
-
-		switch (ret) {
-		case 0:
-			if (bytes_recvd <= 0) {
-				kfree(buffer);
-				return;
-			}
-			desc = (struct vmpacket_descriptor *)buffer;
-
-			switch (desc->type) {
-			case VM_PKT_COMP:
-				break;
-
-			case VM_PKT_DATA_INBAND:
-				mousevsc_on_receive(device, desc);
-				break;
-
-			default:
-				pr_err("unhandled packet type %d, tid %llx len %d\n",
-					desc->type, req_id, bytes_recvd);
-				break;
-			}
 
+	foreach_vmbus_pkt(desc, device->channel) {
+		switch (desc->type) {
+		case VM_PKT_COMP:
 			break;
 
-		case -ENOBUFS:
-			kfree(buffer);
-			/* Handle large packet */
-			bufferlen = bytes_recvd;
-			buffer = kmalloc(bytes_recvd, GFP_ATOMIC);
-
-			if (!buffer)
-				return;
+		case VM_PKT_DATA_INBAND:
+			mousevsc_on_receive(device, desc);
+			break;
 
+		default:
+			pr_err("Unhandled packet type %d, tid %llx len %d\n",
+			       desc->type, desc->trans_id, desc->len8 * 8);
 			break;
 		}
-	} while (1);
-
+	}
 }
 
 static int mousevsc_connect_to_vsp(struct hv_device *device)
-- 
1.8.3.1