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

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Message-Id: <1458350065-32666-5-git-send-email-kys@microsoft.com>
Date:	Fri, 18 Mar 2016 18:14:25 -0700
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	vkuznets@...hat.com, jasowang@...hat.c
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs

Implement copy-free read APIs.

Signed-off-by: K. Y. Srinivasan <kys@...rosoft.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