[PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs

[K. Y. Srinivasan]

Implement copy-free read APIs.

Signed-off-by: K. Y. Srinivasan <k...@microsoft.com>
---
 drivers/hv/ring_buffer.c |   55 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/hyperv.h   |    6 +++++
 2 files changed, 61 insertions(+), 0 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index c2c2b2e..c80e1f3 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -444,3 +444,58 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info 
*inring_info,
 
        return ret;
 }
+
+/*
+ * In-place read functions.
+ */
+bool get_next_pkt_raw(struct vmbus_channel *channel,
+                     struct vmpacket_descriptor **desc)
+{
+       struct hv_ring_buffer_info *ring_info = &channel->inbound;
+       u32 read_loc = ring_info->ring_buffer->read_index;
+       void *ring_buffer = hv_get_ring_buffer(ring_info);
+       struct vmpacket_descriptor *cur_desc;
+       u32 packetlen;
+       u32 dsize = ring_info->ring_datasize;
+       u32 bytes_avail_toread = hv_get_bytes_to_read(ring_info);
+
+       if (bytes_avail_toread < sizeof(struct vmpacket_descriptor))
+               return false;
+
+       if ((read_loc + sizeof(*desc)) > dsize)
+               return false;
+
+       cur_desc = ring_buffer + read_loc;
+       packetlen = cur_desc->len8 << 3;
+
+       if ((read_loc + packetlen + 8) > (dsize - 1))
+               return false;
+
+       *desc = cur_desc;
+       return true;
+}
+EXPORT_SYMBOL_GPL(get_next_pkt_raw);
+
+void put_pkt_raw(struct vmbus_channel *channel,
+                struct vmpacket_descriptor *desc)
+{
+       struct hv_ring_buffer_info *ring_info = &channel->inbound;
+       u32 read_loc = ring_info->ring_buffer->read_index;
+       u32 packetlen = desc->len8 << 3;
+       u32 dsize = ring_info->ring_datasize;
+
+       if ((read_loc + packetlen + 8) > dsize)
+               BUG();
+
+       /*
+        * Make sure all reads are done before we update the read index since
+        * the writer may start writing to the read area once the read index
+        * is updated.
+        */
+       virt_mb();
+       ring_info->ring_buffer->read_index += packetlen + 8;
+
+       if (hv_need_to_signal_on_read(ring_info))
+               vmbus_set_event(channel);
+}
+EXPORT_SYMBOL_GPL(put_pkt_raw);
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index a6b053c..455f3f0 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1035,6 +1035,12 @@ extern int vmbus_recvpacket_raw(struct vmbus_channel 
*channel,
                                     u32 *buffer_actual_len,
                                     u64 *requestid);
 
+bool get_next_pkt_raw(struct vmbus_channel *channel,
+                     struct vmpacket_descriptor **desc);
+
+void put_pkt_raw(struct vmbus_channel *channel,
+                struct vmpacket_descriptor *desc);
+
 
 extern void vmbus_ontimer(unsigned long data);
 
-- 
1.7.4.1