drivers/staging/hv/RingBuffer.c - kernel/prism - Git at Google

 /*
  *
  * Copyright (c) 2009, Microsoft Corporation.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
  * version 2, as published by the Free Software Foundation.
  *
  * This program is distributed in the hope it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  * more details.
  *
  * You should have received a copy of the GNU General Public License along with
  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
  * Place - Suite 330, Boston, MA 02111-1307 USA.
  *
  * Authors:
  *   Haiyang Zhang <haiyangz@microsoft.com>
  *   Hank Janssen  <hjanssen@microsoft.com>
  *
  */

 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include "osd.h"
 #include "logging.h"
 #include "RingBuffer.h"


 /* #defines */


 /* Amount of space to write to */
 #define BYTES_AVAIL_TO_WRITE(r, w, z) ((w) >= (r))?((z) - ((w) - (r))):((r) - (w))


 /*++

 Name:
 	GetRingBufferAvailBytes()

 Description:
 	Get number of bytes available to read and to write to
 	for the specified ring buffer

 --*/
 static inline void
 GetRingBufferAvailBytes(RING_BUFFER_INFO *rbi, u32 *read, u32 *write)
 {
 	u32 read_loc,write_loc;

 	/* Capture the read/write indices before they changed */
 	read_loc = rbi->RingBuffer->ReadIndex;
 	write_loc = rbi->RingBuffer->WriteIndex;

 	*write = BYTES_AVAIL_TO_WRITE(read_loc, write_loc, rbi->RingDataSize);
 	*read = rbi->RingDataSize - *write;
 }

 /*++

 Name:
 	GetNextWriteLocation()

 Description:
 	Get the next write location for the specified ring buffer

 --*/
 static inline u32
 GetNextWriteLocation(RING_BUFFER_INFO* RingInfo)
 {
 	u32 next = RingInfo->RingBuffer->WriteIndex;

 	ASSERT(next < RingInfo->RingDataSize);

 	return next;
 }

 /*++

 Name:
 	SetNextWriteLocation()

 Description:
 	Set the next write location for the specified ring buffer

 --*/
 static inline void
 SetNextWriteLocation(RING_BUFFER_INFO* RingInfo, u32 NextWriteLocation)
 {
 	RingInfo->RingBuffer->WriteIndex = NextWriteLocation;
 }

 /*++

 Name:
 	GetNextReadLocation()

 Description:
 	Get the next read location for the specified ring buffer

 --*/
 static inline u32
 GetNextReadLocation(RING_BUFFER_INFO* RingInfo)
 {
 	u32 next = RingInfo->RingBuffer->ReadIndex;

 	ASSERT(next < RingInfo->RingDataSize);

 	return next;
 }

 /*++

 Name:
 	GetNextReadLocationWithOffset()

 Description:
 	Get the next read location + offset for the specified ring buffer.
 	This allows the caller to skip

 --*/
 static inline u32
 GetNextReadLocationWithOffset(RING_BUFFER_INFO* RingInfo, u32 Offset)
 {
 	u32 next = RingInfo->RingBuffer->ReadIndex;

 	ASSERT(next < RingInfo->RingDataSize);
 	next += Offset;
 	next %= RingInfo->RingDataSize;

 	return next;
 }

 /*++

 Name:
 	SetNextReadLocation()

 Description:
 	Set the next read location for the specified ring buffer

 --*/
 static inline void
 SetNextReadLocation(RING_BUFFER_INFO* RingInfo, u32 NextReadLocation)
 {
 	RingInfo->RingBuffer->ReadIndex = NextReadLocation;
 }


 /*++

 Name:
 	GetRingBuffer()

 Description:
 	Get the start of the ring buffer

 --*/
 static inline void *
 GetRingBuffer(RING_BUFFER_INFO* RingInfo)
 {
 	return (void *)RingInfo->RingBuffer->Buffer;
 }


 /*++

 Name:
 	GetRingBufferSize()

 Description:
 	Get the size of the ring buffer

 --*/
 static inline u32
 GetRingBufferSize(RING_BUFFER_INFO* RingInfo)
 {
 	return RingInfo->RingDataSize;
 }

 /*++

 Name:
 	GetRingBufferIndices()

 Description:
 	Get the read and write indices as u64 of the specified ring buffer

 --*/
 static inline u64
 GetRingBufferIndices(RING_BUFFER_INFO* RingInfo)
 {
 	return ((u64)RingInfo->RingBuffer->WriteIndex << 32) || RingInfo->RingBuffer->ReadIndex;
 }


 /*++

 Name:
 	DumpRingInfo()

 Description:
 	Dump out to console the ring buffer info

 --*/
 void DumpRingInfo(RING_BUFFER_INFO *RingInfo, char *Prefix)
 {
 	u32 bytesAvailToWrite;
 	u32 bytesAvailToRead;

 	GetRingBufferAvailBytes(RingInfo, &bytesAvailToRead, &bytesAvailToWrite);

 	DPRINT(VMBUS, DEBUG_RING_LVL, "%s <<ringinfo %p buffer %p avail write %u avail read %u read idx %u write idx %u>>",
 		Prefix,
 		RingInfo,
 		RingInfo->RingBuffer->Buffer,
 		bytesAvailToWrite,
 		bytesAvailToRead,
 		RingInfo->RingBuffer->ReadIndex,
 		RingInfo->RingBuffer->WriteIndex);
 }


 /* Internal routines */

 static u32
 CopyToRingBuffer(
 	RING_BUFFER_INFO	*RingInfo,
 	u32				StartWriteOffset,
 	void *				Src,
 	u32				SrcLen);

 static u32
 CopyFromRingBuffer(
 	RING_BUFFER_INFO	*RingInfo,
 	void *				Dest,
 	u32				DestLen,
 	u32				StartReadOffset);


 /*++

 Name:
 	RingBufferGetDebugInfo()

 Description:
 	Get various debug metrics for the specified ring buffer

 --*/
 void RingBufferGetDebugInfo(RING_BUFFER_INFO *RingInfo,
 			    RING_BUFFER_DEBUG_INFO *DebugInfo)
 {
 	u32 bytesAvailToWrite;
 	u32 bytesAvailToRead;

 	if (RingInfo->RingBuffer)
 	{
 		GetRingBufferAvailBytes(RingInfo, &bytesAvailToRead, &bytesAvailToWrite);

 		DebugInfo->BytesAvailToRead = bytesAvailToRead;
 		DebugInfo->BytesAvailToWrite = bytesAvailToWrite;
 		DebugInfo->CurrentReadIndex = RingInfo->RingBuffer->ReadIndex;
 		DebugInfo->CurrentWriteIndex = RingInfo->RingBuffer->WriteIndex;

 		DebugInfo->CurrentInterruptMask = RingInfo->RingBuffer->InterruptMask;
 	}
 }


 /*++

 Name:
 	GetRingBufferInterruptMask()

 Description:
 	Get the interrupt mask for the specified ring buffer

 --*/
 u32 GetRingBufferInterruptMask(RING_BUFFER_INFO *rbi)
 {
 	return rbi->RingBuffer->InterruptMask;
 }

 /*++

 Name:
 	RingBufferInit()

 Description:
 	Initialize the ring buffer

 --*/
 int RingBufferInit(RING_BUFFER_INFO *RingInfo, void *Buffer, u32 BufferLen)
 {
 	ASSERT(sizeof(RING_BUFFER) == PAGE_SIZE);

 	memset(RingInfo, 0, sizeof(RING_BUFFER_INFO));

 	RingInfo->RingBuffer = (RING_BUFFER*)Buffer;
 	RingInfo->RingBuffer->ReadIndex = RingInfo->RingBuffer->WriteIndex = 0;

 	RingInfo->RingSize = BufferLen;
 	RingInfo->RingDataSize = BufferLen - sizeof(RING_BUFFER);

 	spin_lock_init(&RingInfo->ring_lock);

 	return 0;
 }

 /*++

 Name:
 	RingBufferCleanup()

 Description:
 	Cleanup the ring buffer

 --*/
 void RingBufferCleanup(RING_BUFFER_INFO* RingInfo)
 {
 }

 /*++

 Name:
 	RingBufferWrite()

 Description:
 	Write to the ring buffer

 --*/
 int RingBufferWrite(RING_BUFFER_INFO *OutRingInfo,
 		    struct scatterlist *sglist, u32 sgcount)
 {
 	int i=0;
 	u32 byteAvailToWrite;
 	u32 byteAvailToRead;
 	u32 totalBytesToWrite=0;

 	struct scatterlist *sg;
 	volatile u32 nextWriteLocation;
 	u64 prevIndices=0;
 	unsigned long flags;

 	DPRINT_ENTER(VMBUS);

 	for_each_sg(sglist, sg, sgcount, i)
 	{
 		totalBytesToWrite += sg->length;
 	}

 	totalBytesToWrite += sizeof(u64);

 	spin_lock_irqsave(&OutRingInfo->ring_lock, flags);

 	GetRingBufferAvailBytes(OutRingInfo, &byteAvailToRead, &byteAvailToWrite);

 	DPRINT_DBG(VMBUS, "Writing %u bytes...", totalBytesToWrite);

 	/* DumpRingInfo(OutRingInfo, "BEFORE "); */

 	/* If there is only room for the packet, assume it is full. Otherwise, the next time around, we think the ring buffer */
 	/* is empty since the read index == write index */
 	if (byteAvailToWrite <= totalBytesToWrite)
 	{
 		DPRINT_DBG(VMBUS, "No more space left on outbound ring buffer (needed %u, avail %u)", totalBytesToWrite, byteAvailToWrite);

 		spin_unlock_irqrestore(&OutRingInfo->ring_lock, flags);

 		DPRINT_EXIT(VMBUS);

 		return -1;
 	}

 	/* Write to the ring buffer */
 	nextWriteLocation = GetNextWriteLocation(OutRingInfo);

 	for_each_sg(sglist, sg, sgcount, i)
 	{
 		nextWriteLocation = CopyToRingBuffer(OutRingInfo,
 						     nextWriteLocation,
 						     sg_virt(sg),
 						     sg->length);
 	}

 	/* Set previous packet start */
 	prevIndices = GetRingBufferIndices(OutRingInfo);

 	nextWriteLocation = CopyToRingBuffer(OutRingInfo,
 					     nextWriteLocation,
 					     &prevIndices,
 					     sizeof(u64));

 	/* Make sure we flush all writes before updating the writeIndex */
 	mb();

 	/* Now, update the write location */
 	SetNextWriteLocation(OutRingInfo, nextWriteLocation);

 	/* DumpRingInfo(OutRingInfo, "AFTER "); */

 	spin_unlock_irqrestore(&OutRingInfo->ring_lock, flags);

 	DPRINT_EXIT(VMBUS);

 	return 0;
 }


 /*++

 Name:
 	RingBufferPeek()

 Description:
 	Read without advancing the read index

 --*/
 int RingBufferPeek(RING_BUFFER_INFO *InRingInfo, void *Buffer, u32 BufferLen)
 {
 	u32 bytesAvailToWrite;
 	u32 bytesAvailToRead;
 	u32 nextReadLocation=0;
 	unsigned long flags;

 	spin_lock_irqsave(&InRingInfo->ring_lock, flags);

 	GetRingBufferAvailBytes(InRingInfo, &bytesAvailToRead, &bytesAvailToWrite);

 	/* Make sure there is something to read */
 	if (bytesAvailToRead < BufferLen )
 	{
 		/* DPRINT_DBG(VMBUS, "got callback but not enough to read <avail to read %d read size %d>!!", bytesAvailToRead, BufferLen); */

 		spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

 		return -1;
 	}

 	/* Convert to byte offset */
 	nextReadLocation = GetNextReadLocation(InRingInfo);

 	nextReadLocation = CopyFromRingBuffer(InRingInfo,
 											Buffer,
 											BufferLen,
 											nextReadLocation);

 	spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

 	return 0;
 }


 /*++

 Name:
 	RingBufferRead()

 Description:
 	Read and advance the read index

 --*/
 int RingBufferRead(RING_BUFFER_INFO *InRingInfo, void *Buffer,
 		   u32 BufferLen, u32 Offset)
 {
 	u32 bytesAvailToWrite;
 	u32 bytesAvailToRead;
 	u32 nextReadLocation=0;
 	u64 prevIndices=0;
 	unsigned long flags;

 	ASSERT(BufferLen > 0);

 	spin_lock_irqsave(&InRingInfo->ring_lock, flags);

 	GetRingBufferAvailBytes(InRingInfo, &bytesAvailToRead, &bytesAvailToWrite);

 	DPRINT_DBG(VMBUS, "Reading %u bytes...", BufferLen);

 	/* DumpRingInfo(InRingInfo, "BEFORE "); */

 	/* Make sure there is something to read */
 	if (bytesAvailToRead < BufferLen )
 	{
 		DPRINT_DBG(VMBUS, "got callback but not enough to read <avail to read %d read size %d>!!", bytesAvailToRead, BufferLen);

 		spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

 		return -1;
 	}

 	nextReadLocation = GetNextReadLocationWithOffset(InRingInfo, Offset);

 	nextReadLocation = CopyFromRingBuffer(InRingInfo,
 											Buffer,
 											BufferLen,
 											nextReadLocation);

 	nextReadLocation = CopyFromRingBuffer(InRingInfo,
 											&prevIndices,
 											sizeof(u64),
 											nextReadLocation);

 	/* 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 */
 	mb();

 	/* Update the read index */
 	SetNextReadLocation(InRingInfo, nextReadLocation);

 	/* DumpRingInfo(InRingInfo, "AFTER "); */

 	spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

 	return 0;
 }


 /*++

 Name:
 	CopyToRingBuffer()

 Description:
 	Helper routine to copy from source to ring buffer.
 	Assume there is enough room. Handles wrap-around in dest case only!!

 --*/
 static u32
 CopyToRingBuffer(
 	RING_BUFFER_INFO	*RingInfo,
 	u32				StartWriteOffset,
 	void *				Src,
 	u32				SrcLen)
 {
 	void * ringBuffer=GetRingBuffer(RingInfo);
 	u32 ringBufferSize=GetRingBufferSize(RingInfo);
 	u32 fragLen;

 	if (SrcLen > ringBufferSize - StartWriteOffset) /* wrap-around detected! */
 	{
 		DPRINT_DBG(VMBUS, "wrap-around detected!");

 		fragLen = ringBufferSize - StartWriteOffset;
 		memcpy(ringBuffer + StartWriteOffset, Src, fragLen);
 		memcpy(ringBuffer, Src + fragLen, SrcLen - fragLen);
 	}
 	else
 	{
 		memcpy(ringBuffer + StartWriteOffset, Src, SrcLen);
 	}

 	StartWriteOffset += SrcLen;
 	StartWriteOffset %= ringBufferSize;

 	return StartWriteOffset;
 }


 /*++

 Name:
 	CopyFromRingBuffer()

 Description:
 	Helper routine to copy to source from ring buffer.
 	Assume there is enough room. Handles wrap-around in src case only!!

 --*/
 static u32
 CopyFromRingBuffer(
 	RING_BUFFER_INFO	*RingInfo,
 	void *				Dest,
 	u32				DestLen,
 	u32				StartReadOffset)
 {
 	void * ringBuffer=GetRingBuffer(RingInfo);
 	u32 ringBufferSize=GetRingBufferSize(RingInfo);

 	u32 fragLen;

 	if (DestLen > ringBufferSize - StartReadOffset) /* wrap-around detected at the src */
 	{
 		DPRINT_DBG(VMBUS, "src wrap-around detected!");

 		fragLen = ringBufferSize - StartReadOffset;

 		memcpy(Dest, ringBuffer + StartReadOffset, fragLen);
 		memcpy(Dest + fragLen, ringBuffer, DestLen - fragLen);
 	}
 	else
 	{
 		memcpy(Dest, ringBuffer + StartReadOffset, DestLen);
 	}

 	StartReadOffset += DestLen;
 	StartReadOffset %= ringBufferSize;

 	return StartReadOffset;
 }


 /* eof */
	/*
	*
	* Copyright (c) 2009, Microsoft Corporation.
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms and conditions of the GNU General Public License,
	* version 2, as published by the Free Software Foundation.
	*
	* This program is distributed in the hope it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	* more details.
	*
	* You should have received a copy of the GNU General Public License along with
	* this program; if not, write to the Free Software Foundation, Inc., 59 Temple
	* Place - Suite 330, Boston, MA 02111-1307 USA.
	*
	* Authors:
	* Haiyang Zhang <haiyangz@microsoft.com>
	* Hank Janssen <hjanssen@microsoft.com>
	*
	*/

	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include "osd.h"
	#include "logging.h"
	#include "RingBuffer.h"


	/* #defines */


	/* Amount of space to write to */
	#define BYTES_AVAIL_TO_WRITE(r, w, z) ((w) >= (r))?((z) - ((w) - (r))):((r) - (w))


	/*++

	Name:
	GetRingBufferAvailBytes()

	Description:
	Get number of bytes available to read and to write to
	for the specified ring buffer

	--*/
	static inline void
	GetRingBufferAvailBytes(RING_BUFFER_INFO rbi, u32 read, u32 *write)
	{
	u32 read_loc,write_loc;

	/* Capture the read/write indices before they changed */
	read_loc = rbi->RingBuffer->ReadIndex;
	write_loc = rbi->RingBuffer->WriteIndex;

	*write = BYTES_AVAIL_TO_WRITE(read_loc, write_loc, rbi->RingDataSize);
	read = rbi->RingDataSize - write;
	}

	/*++

	Name:
	GetNextWriteLocation()

	Description:
	Get the next write location for the specified ring buffer

	--*/
	static inline u32
	GetNextWriteLocation(RING_BUFFER_INFO* RingInfo)
	{
	u32 next = RingInfo->RingBuffer->WriteIndex;

	ASSERT(next < RingInfo->RingDataSize);

	return next;
	}

	/*++

	Name:
	SetNextWriteLocation()

	Description:
	Set the next write location for the specified ring buffer

	--*/
	static inline void
	SetNextWriteLocation(RING_BUFFER_INFO* RingInfo, u32 NextWriteLocation)
	{
	RingInfo->RingBuffer->WriteIndex = NextWriteLocation;
	}

	/*++

	Name:
	GetNextReadLocation()

	Description:
	Get the next read location for the specified ring buffer

	--*/
	static inline u32
	GetNextReadLocation(RING_BUFFER_INFO* RingInfo)
	{
	u32 next = RingInfo->RingBuffer->ReadIndex;

	ASSERT(next < RingInfo->RingDataSize);

	return next;
	}

	/*++

	Name:
	GetNextReadLocationWithOffset()

	Description:
	Get the next read location + offset for the specified ring buffer.
	This allows the caller to skip

	--*/
	static inline u32
	GetNextReadLocationWithOffset(RING_BUFFER_INFO* RingInfo, u32 Offset)
	{
	u32 next = RingInfo->RingBuffer->ReadIndex;

	ASSERT(next < RingInfo->RingDataSize);
	next += Offset;
	next %= RingInfo->RingDataSize;

	return next;
	}

	/*++

	Name:
	SetNextReadLocation()

	Description:
	Set the next read location for the specified ring buffer

	--*/
	static inline void
	SetNextReadLocation(RING_BUFFER_INFO* RingInfo, u32 NextReadLocation)
	{
	RingInfo->RingBuffer->ReadIndex = NextReadLocation;
	}


	/*++

	Name:
	GetRingBuffer()

	Description:
	Get the start of the ring buffer

	--*/
	static inline void *
	GetRingBuffer(RING_BUFFER_INFO* RingInfo)
	{
	return (void *)RingInfo->RingBuffer->Buffer;
	}


	/*++

	Name:
	GetRingBufferSize()

	Description:
	Get the size of the ring buffer

	--*/
	static inline u32
	GetRingBufferSize(RING_BUFFER_INFO* RingInfo)
	{
	return RingInfo->RingDataSize;
	}

	/*++

	Name:
	GetRingBufferIndices()

	Description:
	Get the read and write indices as u64 of the specified ring buffer

	--*/
	static inline u64
	GetRingBufferIndices(RING_BUFFER_INFO* RingInfo)
	{
	return ((u64)RingInfo->RingBuffer->WriteIndex << 32) \|\| RingInfo->RingBuffer->ReadIndex;
	}


	/*++

	Name:
	DumpRingInfo()

	Description:
	Dump out to console the ring buffer info

	--*/
	void DumpRingInfo(RING_BUFFER_INFO RingInfo, char Prefix)
	{
	u32 bytesAvailToWrite;
	u32 bytesAvailToRead;

	GetRingBufferAvailBytes(RingInfo, &bytesAvailToRead, &bytesAvailToWrite);

	DPRINT(VMBUS, DEBUG_RING_LVL, "%s <<ringinfo %p buffer %p avail write %u avail read %u read idx %u write idx %u>>",
	Prefix,
	RingInfo,
	RingInfo->RingBuffer->Buffer,
	bytesAvailToWrite,
	bytesAvailToRead,
	RingInfo->RingBuffer->ReadIndex,
	RingInfo->RingBuffer->WriteIndex);
	}


	/* Internal routines */

	static u32
	CopyToRingBuffer(
	RING_BUFFER_INFO *RingInfo,
	u32 StartWriteOffset,
	void * Src,
	u32 SrcLen);

	static u32
	CopyFromRingBuffer(
	RING_BUFFER_INFO *RingInfo,
	void * Dest,
	u32 DestLen,
	u32 StartReadOffset);



	/*++

	Name:
	RingBufferGetDebugInfo()

	Description:
	Get various debug metrics for the specified ring buffer

	--*/
	void RingBufferGetDebugInfo(RING_BUFFER_INFO *RingInfo,
	RING_BUFFER_DEBUG_INFO *DebugInfo)
	{
	u32 bytesAvailToWrite;
	u32 bytesAvailToRead;

	if (RingInfo->RingBuffer)
	{
	GetRingBufferAvailBytes(RingInfo, &bytesAvailToRead, &bytesAvailToWrite);

	DebugInfo->BytesAvailToRead = bytesAvailToRead;
	DebugInfo->BytesAvailToWrite = bytesAvailToWrite;
	DebugInfo->CurrentReadIndex = RingInfo->RingBuffer->ReadIndex;
	DebugInfo->CurrentWriteIndex = RingInfo->RingBuffer->WriteIndex;

	DebugInfo->CurrentInterruptMask = RingInfo->RingBuffer->InterruptMask;
	}
	}


	/*++

	Name:
	GetRingBufferInterruptMask()

	Description:
	Get the interrupt mask for the specified ring buffer

	--*/
	u32 GetRingBufferInterruptMask(RING_BUFFER_INFO *rbi)
	{
	return rbi->RingBuffer->InterruptMask;
	}

	/*++

	Name:
	RingBufferInit()

	Description:
	Initialize the ring buffer

	--*/
	int RingBufferInit(RING_BUFFER_INFO RingInfo, void Buffer, u32 BufferLen)
	{
	ASSERT(sizeof(RING_BUFFER) == PAGE_SIZE);

	memset(RingInfo, 0, sizeof(RING_BUFFER_INFO));

	RingInfo->RingBuffer = (RING_BUFFER*)Buffer;
	RingInfo->RingBuffer->ReadIndex = RingInfo->RingBuffer->WriteIndex = 0;

	RingInfo->RingSize = BufferLen;
	RingInfo->RingDataSize = BufferLen - sizeof(RING_BUFFER);

	spin_lock_init(&RingInfo->ring_lock);

	return 0;
	}

	/*++

	Name:
	RingBufferCleanup()

	Description:
	Cleanup the ring buffer

	--*/
	void RingBufferCleanup(RING_BUFFER_INFO* RingInfo)
	{
	}

	/*++

	Name:
	RingBufferWrite()

	Description:
	Write to the ring buffer

	--*/
	int RingBufferWrite(RING_BUFFER_INFO *OutRingInfo,
	struct scatterlist *sglist, u32 sgcount)
	{
	int i=0;
	u32 byteAvailToWrite;
	u32 byteAvailToRead;
	u32 totalBytesToWrite=0;

	struct scatterlist *sg;
	volatile u32 nextWriteLocation;
	u64 prevIndices=0;
	unsigned long flags;

	DPRINT_ENTER(VMBUS);

	for_each_sg(sglist, sg, sgcount, i)
	{
	totalBytesToWrite += sg->length;
	}

	totalBytesToWrite += sizeof(u64);

	spin_lock_irqsave(&OutRingInfo->ring_lock, flags);

	GetRingBufferAvailBytes(OutRingInfo, &byteAvailToRead, &byteAvailToWrite);

	DPRINT_DBG(VMBUS, "Writing %u bytes...", totalBytesToWrite);

	/* DumpRingInfo(OutRingInfo, "BEFORE "); */

	/* If there is only room for the packet, assume it is full. Otherwise, the next time around, we think the ring buffer */
	/* is empty since the read index == write index */
	if (byteAvailToWrite <= totalBytesToWrite)
	{
	DPRINT_DBG(VMBUS, "No more space left on outbound ring buffer (needed %u, avail %u)", totalBytesToWrite, byteAvailToWrite);

	spin_unlock_irqrestore(&OutRingInfo->ring_lock, flags);

	DPRINT_EXIT(VMBUS);

	return -1;
	}

	/* Write to the ring buffer */
	nextWriteLocation = GetNextWriteLocation(OutRingInfo);

	for_each_sg(sglist, sg, sgcount, i)
	{
	nextWriteLocation = CopyToRingBuffer(OutRingInfo,
	nextWriteLocation,
	sg_virt(sg),
	sg->length);
	}

	/* Set previous packet start */
	prevIndices = GetRingBufferIndices(OutRingInfo);

	nextWriteLocation = CopyToRingBuffer(OutRingInfo,
	nextWriteLocation,
	&prevIndices,
	sizeof(u64));

	/* Make sure we flush all writes before updating the writeIndex */
	mb();

	/* Now, update the write location */
	SetNextWriteLocation(OutRingInfo, nextWriteLocation);

	/* DumpRingInfo(OutRingInfo, "AFTER "); */

	spin_unlock_irqrestore(&OutRingInfo->ring_lock, flags);

	DPRINT_EXIT(VMBUS);

	return 0;
	}


	/*++

	Name:
	RingBufferPeek()

	Description:
	Read without advancing the read index

	--*/
	int RingBufferPeek(RING_BUFFER_INFO InRingInfo, void Buffer, u32 BufferLen)
	{
	u32 bytesAvailToWrite;
	u32 bytesAvailToRead;
	u32 nextReadLocation=0;
	unsigned long flags;

	spin_lock_irqsave(&InRingInfo->ring_lock, flags);

	GetRingBufferAvailBytes(InRingInfo, &bytesAvailToRead, &bytesAvailToWrite);

	/* Make sure there is something to read */
	if (bytesAvailToRead < BufferLen )
	{
	/* DPRINT_DBG(VMBUS, "got callback but not enough to read <avail to read %d read size %d>!!", bytesAvailToRead, BufferLen); */

	spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

	return -1;
	}

	/* Convert to byte offset */
	nextReadLocation = GetNextReadLocation(InRingInfo);

	nextReadLocation = CopyFromRingBuffer(InRingInfo,
	Buffer,
	BufferLen,
	nextReadLocation);

	spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

	return 0;
	}


	/*++

	Name:
	RingBufferRead()

	Description:
	Read and advance the read index

	--*/
	int RingBufferRead(RING_BUFFER_INFO InRingInfo, void Buffer,
	u32 BufferLen, u32 Offset)
	{
	u32 bytesAvailToWrite;
	u32 bytesAvailToRead;
	u32 nextReadLocation=0;
	u64 prevIndices=0;
	unsigned long flags;

	ASSERT(BufferLen > 0);

	spin_lock_irqsave(&InRingInfo->ring_lock, flags);

	GetRingBufferAvailBytes(InRingInfo, &bytesAvailToRead, &bytesAvailToWrite);

	DPRINT_DBG(VMBUS, "Reading %u bytes...", BufferLen);

	/* DumpRingInfo(InRingInfo, "BEFORE "); */

	/* Make sure there is something to read */
	if (bytesAvailToRead < BufferLen )
	{
	DPRINT_DBG(VMBUS, "got callback but not enough to read <avail to read %d read size %d>!!", bytesAvailToRead, BufferLen);

	spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

	return -1;
	}

	nextReadLocation = GetNextReadLocationWithOffset(InRingInfo, Offset);

	nextReadLocation = CopyFromRingBuffer(InRingInfo,
	Buffer,
	BufferLen,
	nextReadLocation);

	nextReadLocation = CopyFromRingBuffer(InRingInfo,
	&prevIndices,
	sizeof(u64),
	nextReadLocation);

	/* 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 */
	mb();

	/* Update the read index */
	SetNextReadLocation(InRingInfo, nextReadLocation);

	/* DumpRingInfo(InRingInfo, "AFTER "); */

	spin_unlock_irqrestore(&InRingInfo->ring_lock, flags);

	return 0;
	}


	/*++

	Name:
	CopyToRingBuffer()

	Description:
	Helper routine to copy from source to ring buffer.
	Assume there is enough room. Handles wrap-around in dest case only!!

	--*/
	static u32
	CopyToRingBuffer(
	RING_BUFFER_INFO *RingInfo,
	u32 StartWriteOffset,
	void * Src,
	u32 SrcLen)
	{
	void * ringBuffer=GetRingBuffer(RingInfo);
	u32 ringBufferSize=GetRingBufferSize(RingInfo);
	u32 fragLen;

	if (SrcLen > ringBufferSize - StartWriteOffset) /* wrap-around detected! */
	{
	DPRINT_DBG(VMBUS, "wrap-around detected!");

	fragLen = ringBufferSize - StartWriteOffset;
	memcpy(ringBuffer + StartWriteOffset, Src, fragLen);
	memcpy(ringBuffer, Src + fragLen, SrcLen - fragLen);
	}
	else
	{
	memcpy(ringBuffer + StartWriteOffset, Src, SrcLen);
	}

	StartWriteOffset += SrcLen;
	StartWriteOffset %= ringBufferSize;

	return StartWriteOffset;
	}


	/*++

	Name:
	CopyFromRingBuffer()

	Description:
	Helper routine to copy to source from ring buffer.
	Assume there is enough room. Handles wrap-around in src case only!!

	--*/
	static u32
	CopyFromRingBuffer(
	RING_BUFFER_INFO *RingInfo,
	void * Dest,
	u32 DestLen,
	u32 StartReadOffset)
	{
	void * ringBuffer=GetRingBuffer(RingInfo);
	u32 ringBufferSize=GetRingBufferSize(RingInfo);

	u32 fragLen;

	if (DestLen > ringBufferSize - StartReadOffset) /* wrap-around detected at the src */
	{
	DPRINT_DBG(VMBUS, "src wrap-around detected!");

	fragLen = ringBufferSize - StartReadOffset;

	memcpy(Dest, ringBuffer + StartReadOffset, fragLen);
	memcpy(Dest + fragLen, ringBuffer, DestLen - fragLen);
	}
	else
	{
	memcpy(Dest, ringBuffer + StartReadOffset, DestLen);
	}

	StartReadOffset += DestLen;
	StartReadOffset %= ringBufferSize;

	return StartReadOffset;
	}


	/* eof */