drivers/hv/ring_buffer.c - kernel/mindspeed - 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>
  *   K. Y. Srinivasan <kys@microsoft.com>
  *
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/hyperv.h>

 #include "hyperv_vmbus.h"


 /* #defines */


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


 /*
  *
  * hv_get_ringbuffer_availbytes()
  *
  * Get number of bytes available to read and to write to
  * for the specified ring buffer
  */
 static inline void
 hv_get_ringbuffer_availbytes(struct hv_ring_buffer_info *rbi,
 			  u32 *read, u32 *write)
 {
 	u32 read_loc, write_loc;

 	smp_read_barrier_depends();

 	/* Capture the read/write indices before they changed */
 	read_loc = rbi->ring_buffer->read_index;
 	write_loc = rbi->ring_buffer->write_index;

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

 /*
  * hv_get_next_write_location()
  *
  * Get the next write location for the specified ring buffer
  *
  */
 static inline u32
 hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
 {
 	u32 next = ring_info->ring_buffer->write_index;

 	return next;
 }

 /*
  * hv_set_next_write_location()
  *
  * Set the next write location for the specified ring buffer
  *
  */
 static inline void
 hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
 		     u32 next_write_location)
 {
 	ring_info->ring_buffer->write_index = next_write_location;
 }

 /*
  * hv_get_next_read_location()
  *
  * Get the next read location for the specified ring buffer
  */
 static inline u32
 hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
 {
 	u32 next = ring_info->ring_buffer->read_index;

 	return next;
 }

 /*
  * hv_get_next_readlocation_withoffset()
  *
  * Get the next read location + offset for the specified ring buffer.
  * This allows the caller to skip
  */
 static inline u32
 hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
 				 u32 offset)
 {
 	u32 next = ring_info->ring_buffer->read_index;

 	next += offset;
 	next %= ring_info->ring_datasize;

 	return next;
 }

 /*
  *
  * hv_set_next_read_location()
  *
  * Set the next read location for the specified ring buffer
  *
  */
 static inline void
 hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
 		    u32 next_read_location)
 {
 	ring_info->ring_buffer->read_index = next_read_location;
 }


 /*
  *
  * hv_get_ring_buffer()
  *
  * Get the start of the ring buffer
  */
 static inline void *
 hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
 {
 	return (void *)ring_info->ring_buffer->buffer;
 }


 /*
  *
  * hv_get_ring_buffersize()
  *
  * Get the size of the ring buffer
  */
 static inline u32
 hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
 {
 	return ring_info->ring_datasize;
 }

 /*
  *
  * hv_get_ring_bufferindices()
  *
  * Get the read and write indices as u64 of the specified ring buffer
  *
  */
 static inline u64
 hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
 {
 	return (u64)ring_info->ring_buffer->write_index << 32;
 }

 /*
  *
  * hv_copyfrom_ringbuffer()
  *
  * Helper routine to copy to source from ring buffer.
  * Assume there is enough room. Handles wrap-around in src case only!!
  *
  */
 static u32 hv_copyfrom_ringbuffer(
 	struct hv_ring_buffer_info	*ring_info,
 	void				*dest,
 	u32				destlen,
 	u32				start_read_offset)
 {
 	void *ring_buffer = hv_get_ring_buffer(ring_info);
 	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);

 	u32 frag_len;

 	/* wrap-around detected at the src */
 	if (destlen > ring_buffer_size - start_read_offset) {
 		frag_len = ring_buffer_size - start_read_offset;

 		memcpy(dest, ring_buffer + start_read_offset, frag_len);
 		memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
 	} else

 		memcpy(dest, ring_buffer + start_read_offset, destlen);


 	start_read_offset += destlen;
 	start_read_offset %= ring_buffer_size;

 	return start_read_offset;
 }


 /*
  *
  * hv_copyto_ringbuffer()
  *
  * Helper routine to copy from source to ring buffer.
  * Assume there is enough room. Handles wrap-around in dest case only!!
  *
  */
 static u32 hv_copyto_ringbuffer(
 	struct hv_ring_buffer_info	*ring_info,
 	u32				start_write_offset,
 	void				*src,
 	u32				srclen)
 {
 	void *ring_buffer = hv_get_ring_buffer(ring_info);
 	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 	u32 frag_len;

 	/* wrap-around detected! */
 	if (srclen > ring_buffer_size - start_write_offset) {
 		frag_len = ring_buffer_size - start_write_offset;
 		memcpy(ring_buffer + start_write_offset, src, frag_len);
 		memcpy(ring_buffer, src + frag_len, srclen - frag_len);
 	} else
 		memcpy(ring_buffer + start_write_offset, src, srclen);

 	start_write_offset += srclen;
 	start_write_offset %= ring_buffer_size;

 	return start_write_offset;
 }

 /*
  *
  * hv_ringbuffer_get_debuginfo()
  *
  * Get various debug metrics for the specified ring buffer
  *
  */
 void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 			    struct hv_ring_buffer_debug_info *debug_info)
 {
 	u32 bytes_avail_towrite;
 	u32 bytes_avail_toread;

 	if (ring_info->ring_buffer) {
 		hv_get_ringbuffer_availbytes(ring_info,
 					&bytes_avail_toread,
 					&bytes_avail_towrite);

 		debug_info->bytes_avail_toread = bytes_avail_toread;
 		debug_info->bytes_avail_towrite = bytes_avail_towrite;
 		debug_info->current_read_index =
 			ring_info->ring_buffer->read_index;
 		debug_info->current_write_index =
 			ring_info->ring_buffer->write_index;
 		debug_info->current_interrupt_mask =
 			ring_info->ring_buffer->interrupt_mask;
 	}
 }


 /*
  *
  * hv_get_ringbuffer_interrupt_mask()
  *
  * Get the interrupt mask for the specified ring buffer
  *
  */
 u32 hv_get_ringbuffer_interrupt_mask(struct hv_ring_buffer_info *rbi)
 {
 	return rbi->ring_buffer->interrupt_mask;
 }

 /*
  *
  * hv_ringbuffer_init()
  *
  *Initialize the ring buffer
  *
  */
 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 		   void *buffer, u32 buflen)
 {
 	if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
 		return -EINVAL;

 	memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));

 	ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
 	ring_info->ring_buffer->read_index =
 		ring_info->ring_buffer->write_index = 0;

 	ring_info->ring_size = buflen;
 	ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);

 	spin_lock_init(&ring_info->ring_lock);

 	return 0;
 }

 /*
  *
  * hv_ringbuffer_cleanup()
  *
  * Cleanup the ring buffer
  *
  */
 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 {
 }

 /*
  *
  * hv_ringbuffer_write()
  *
  * Write to the ring buffer
  *
  */
 int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
 		    struct scatterlist *sglist, u32 sgcount)
 {
 	int i = 0;
 	u32 bytes_avail_towrite;
 	u32 bytes_avail_toread;
 	u32 totalbytes_towrite = 0;

 	struct scatterlist *sg;
 	u32 next_write_location;
 	u64 prev_indices = 0;
 	unsigned long flags;

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

 	totalbytes_towrite += sizeof(u64);

 	spin_lock_irqsave(&outring_info->ring_lock, flags);

 	hv_get_ringbuffer_availbytes(outring_info,
 				&bytes_avail_toread,
 				&bytes_avail_towrite);


 	/* 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 (bytes_avail_towrite <= totalbytes_towrite) {
 		spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 		return -EAGAIN;
 	}

 	/* Write to the ring buffer */
 	next_write_location = hv_get_next_write_location(outring_info);

 	for_each_sg(sglist, sg, sgcount, i)
 	{
 		next_write_location = hv_copyto_ringbuffer(outring_info,
 						     next_write_location,
 						     sg_virt(sg),
 						     sg->length);
 	}

 	/* Set previous packet start */
 	prev_indices = hv_get_ring_bufferindices(outring_info);

 	next_write_location = hv_copyto_ringbuffer(outring_info,
 					     next_write_location,
 					     &prev_indices,
 					     sizeof(u64));

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

 	/* Now, update the write location */
 	hv_set_next_write_location(outring_info, next_write_location);


 	spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 	return 0;
 }


 /*
  *
  * hv_ringbuffer_peek()
  *
  * Read without advancing the read index
  *
  */
 int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
 		   void *Buffer, u32 buflen)
 {
 	u32 bytes_avail_towrite;
 	u32 bytes_avail_toread;
 	u32 next_read_location = 0;
 	unsigned long flags;

 	spin_lock_irqsave(&Inring_info->ring_lock, flags);

 	hv_get_ringbuffer_availbytes(Inring_info,
 				&bytes_avail_toread,
 				&bytes_avail_towrite);

 	/* Make sure there is something to read */
 	if (bytes_avail_toread < buflen) {

 		spin_unlock_irqrestore(&Inring_info->ring_lock, flags);

 		return -EAGAIN;
 	}

 	/* Convert to byte offset */
 	next_read_location = hv_get_next_read_location(Inring_info);

 	next_read_location = hv_copyfrom_ringbuffer(Inring_info,
 						Buffer,
 						buflen,
 						next_read_location);

 	spin_unlock_irqrestore(&Inring_info->ring_lock, flags);

 	return 0;
 }


 /*
  *
  * hv_ringbuffer_read()
  *
  * Read and advance the read index
  *
  */
 int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
 		   u32 buflen, u32 offset)
 {
 	u32 bytes_avail_towrite;
 	u32 bytes_avail_toread;
 	u32 next_read_location = 0;
 	u64 prev_indices = 0;
 	unsigned long flags;

 	if (buflen <= 0)
 		return -EINVAL;

 	spin_lock_irqsave(&inring_info->ring_lock, flags);

 	hv_get_ringbuffer_availbytes(inring_info,
 				&bytes_avail_toread,
 				&bytes_avail_towrite);

 	/* Make sure there is something to read */
 	if (bytes_avail_toread < buflen) {
 		spin_unlock_irqrestore(&inring_info->ring_lock, flags);

 		return -EAGAIN;
 	}

 	next_read_location =
 		hv_get_next_readlocation_withoffset(inring_info, offset);

 	next_read_location = hv_copyfrom_ringbuffer(inring_info,
 						buffer,
 						buflen,
 						next_read_location);

 	next_read_location = hv_copyfrom_ringbuffer(inring_info,
 						&prev_indices,
 						sizeof(u64),
 						next_read_location);

 	/* 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 */
 	smp_mb();

 	/* Update the read index */
 	hv_set_next_read_location(inring_info, next_read_location);

 	spin_unlock_irqrestore(&inring_info->ring_lock, flags);

 	return 0;
 }
	/*
	*
	* 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>
	* K. Y. Srinivasan <kys@microsoft.com>
	*
	*/
	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include <linux/hyperv.h>

	#include "hyperv_vmbus.h"


	/* #defines */


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


	/*
	*
	* hv_get_ringbuffer_availbytes()
	*
	* Get number of bytes available to read and to write to
	* for the specified ring buffer
	*/
	static inline void
	hv_get_ringbuffer_availbytes(struct hv_ring_buffer_info *rbi,
	u32 read, u32 write)
	{
	u32 read_loc, write_loc;

	smp_read_barrier_depends();

	/* Capture the read/write indices before they changed */
	read_loc = rbi->ring_buffer->read_index;
	write_loc = rbi->ring_buffer->write_index;

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

	/*
	* hv_get_next_write_location()
	*
	* Get the next write location for the specified ring buffer
	*
	*/
	static inline u32
	hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
	{
	u32 next = ring_info->ring_buffer->write_index;

	return next;
	}

	/*
	* hv_set_next_write_location()
	*
	* Set the next write location for the specified ring buffer
	*
	*/
	static inline void
	hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
	u32 next_write_location)
	{
	ring_info->ring_buffer->write_index = next_write_location;
	}

	/*
	* hv_get_next_read_location()
	*
	* Get the next read location for the specified ring buffer
	*/
	static inline u32
	hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
	{
	u32 next = ring_info->ring_buffer->read_index;

	return next;
	}

	/*
	* hv_get_next_readlocation_withoffset()
	*
	* Get the next read location + offset for the specified ring buffer.
	* This allows the caller to skip
	*/
	static inline u32
	hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
	u32 offset)
	{
	u32 next = ring_info->ring_buffer->read_index;

	next += offset;
	next %= ring_info->ring_datasize;

	return next;
	}

	/*
	*
	* hv_set_next_read_location()
	*
	* Set the next read location for the specified ring buffer
	*
	*/
	static inline void
	hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
	u32 next_read_location)
	{
	ring_info->ring_buffer->read_index = next_read_location;
	}


	/*
	*
	* hv_get_ring_buffer()
	*
	* Get the start of the ring buffer
	*/
	static inline void *
	hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
	{
	return (void *)ring_info->ring_buffer->buffer;
	}


	/*
	*
	* hv_get_ring_buffersize()
	*
	* Get the size of the ring buffer
	*/
	static inline u32
	hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
	{
	return ring_info->ring_datasize;
	}

	/*
	*
	* hv_get_ring_bufferindices()
	*
	* Get the read and write indices as u64 of the specified ring buffer
	*
	*/
	static inline u64
	hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
	{
	return (u64)ring_info->ring_buffer->write_index << 32;
	}

	/*
	*
	* hv_copyfrom_ringbuffer()
	*
	* Helper routine to copy to source from ring buffer.
	* Assume there is enough room. Handles wrap-around in src case only!!
	*
	*/
	static u32 hv_copyfrom_ringbuffer(
	struct hv_ring_buffer_info *ring_info,
	void *dest,
	u32 destlen,
	u32 start_read_offset)
	{
	void *ring_buffer = hv_get_ring_buffer(ring_info);
	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);

	u32 frag_len;

	/* wrap-around detected at the src */
	if (destlen > ring_buffer_size - start_read_offset) {
	frag_len = ring_buffer_size - start_read_offset;

	memcpy(dest, ring_buffer + start_read_offset, frag_len);
	memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
	} else

	memcpy(dest, ring_buffer + start_read_offset, destlen);


	start_read_offset += destlen;
	start_read_offset %= ring_buffer_size;

	return start_read_offset;
	}


	/*
	*
	* hv_copyto_ringbuffer()
	*
	* Helper routine to copy from source to ring buffer.
	* Assume there is enough room. Handles wrap-around in dest case only!!
	*
	*/
	static u32 hv_copyto_ringbuffer(
	struct hv_ring_buffer_info *ring_info,
	u32 start_write_offset,
	void *src,
	u32 srclen)
	{
	void *ring_buffer = hv_get_ring_buffer(ring_info);
	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
	u32 frag_len;

	/* wrap-around detected! */
	if (srclen > ring_buffer_size - start_write_offset) {
	frag_len = ring_buffer_size - start_write_offset;
	memcpy(ring_buffer + start_write_offset, src, frag_len);
	memcpy(ring_buffer, src + frag_len, srclen - frag_len);
	} else
	memcpy(ring_buffer + start_write_offset, src, srclen);

	start_write_offset += srclen;
	start_write_offset %= ring_buffer_size;

	return start_write_offset;
	}

	/*
	*
	* hv_ringbuffer_get_debuginfo()
	*
	* Get various debug metrics for the specified ring buffer
	*
	*/
	void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
	struct hv_ring_buffer_debug_info *debug_info)
	{
	u32 bytes_avail_towrite;
	u32 bytes_avail_toread;

	if (ring_info->ring_buffer) {
	hv_get_ringbuffer_availbytes(ring_info,
	&bytes_avail_toread,
	&bytes_avail_towrite);

	debug_info->bytes_avail_toread = bytes_avail_toread;
	debug_info->bytes_avail_towrite = bytes_avail_towrite;
	debug_info->current_read_index =
	ring_info->ring_buffer->read_index;
	debug_info->current_write_index =
	ring_info->ring_buffer->write_index;
	debug_info->current_interrupt_mask =
	ring_info->ring_buffer->interrupt_mask;
	}
	}


	/*
	*
	* hv_get_ringbuffer_interrupt_mask()
	*
	* Get the interrupt mask for the specified ring buffer
	*
	*/
	u32 hv_get_ringbuffer_interrupt_mask(struct hv_ring_buffer_info *rbi)
	{
	return rbi->ring_buffer->interrupt_mask;
	}

	/*
	*
	* hv_ringbuffer_init()
	*
	*Initialize the ring buffer
	*
	*/
	int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
	void *buffer, u32 buflen)
	{
	if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
	return -EINVAL;

	memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));

	ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
	ring_info->ring_buffer->read_index =
	ring_info->ring_buffer->write_index = 0;

	ring_info->ring_size = buflen;
	ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);

	spin_lock_init(&ring_info->ring_lock);

	return 0;
	}

	/*
	*
	* hv_ringbuffer_cleanup()
	*
	* Cleanup the ring buffer
	*
	*/
	void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
	{
	}

	/*
	*
	* hv_ringbuffer_write()
	*
	* Write to the ring buffer
	*
	*/
	int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
	struct scatterlist *sglist, u32 sgcount)
	{
	int i = 0;
	u32 bytes_avail_towrite;
	u32 bytes_avail_toread;
	u32 totalbytes_towrite = 0;

	struct scatterlist *sg;
	u32 next_write_location;
	u64 prev_indices = 0;
	unsigned long flags;

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

	totalbytes_towrite += sizeof(u64);

	spin_lock_irqsave(&outring_info->ring_lock, flags);

	hv_get_ringbuffer_availbytes(outring_info,
	&bytes_avail_toread,
	&bytes_avail_towrite);


	/* 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 (bytes_avail_towrite <= totalbytes_towrite) {
	spin_unlock_irqrestore(&outring_info->ring_lock, flags);
	return -EAGAIN;
	}

	/* Write to the ring buffer */
	next_write_location = hv_get_next_write_location(outring_info);

	for_each_sg(sglist, sg, sgcount, i)
	{
	next_write_location = hv_copyto_ringbuffer(outring_info,
	next_write_location,
	sg_virt(sg),
	sg->length);
	}

	/* Set previous packet start */
	prev_indices = hv_get_ring_bufferindices(outring_info);

	next_write_location = hv_copyto_ringbuffer(outring_info,
	next_write_location,
	&prev_indices,
	sizeof(u64));

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

	/* Now, update the write location */
	hv_set_next_write_location(outring_info, next_write_location);


	spin_unlock_irqrestore(&outring_info->ring_lock, flags);
	return 0;
	}


	/*
	*
	* hv_ringbuffer_peek()
	*
	* Read without advancing the read index
	*
	*/
	int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
	void *Buffer, u32 buflen)
	{
	u32 bytes_avail_towrite;
	u32 bytes_avail_toread;
	u32 next_read_location = 0;
	unsigned long flags;

	spin_lock_irqsave(&Inring_info->ring_lock, flags);

	hv_get_ringbuffer_availbytes(Inring_info,
	&bytes_avail_toread,
	&bytes_avail_towrite);

	/* Make sure there is something to read */
	if (bytes_avail_toread < buflen) {

	spin_unlock_irqrestore(&Inring_info->ring_lock, flags);

	return -EAGAIN;
	}

	/* Convert to byte offset */
	next_read_location = hv_get_next_read_location(Inring_info);

	next_read_location = hv_copyfrom_ringbuffer(Inring_info,
	Buffer,
	buflen,
	next_read_location);

	spin_unlock_irqrestore(&Inring_info->ring_lock, flags);

	return 0;
	}


	/*
	*
	* hv_ringbuffer_read()
	*
	* Read and advance the read index
	*
	*/
	int hv_ringbuffer_read(struct hv_ring_buffer_info inring_info, void buffer,
	u32 buflen, u32 offset)
	{
	u32 bytes_avail_towrite;
	u32 bytes_avail_toread;
	u32 next_read_location = 0;
	u64 prev_indices = 0;
	unsigned long flags;

	if (buflen <= 0)
	return -EINVAL;

	spin_lock_irqsave(&inring_info->ring_lock, flags);

	hv_get_ringbuffer_availbytes(inring_info,
	&bytes_avail_toread,
	&bytes_avail_towrite);

	/* Make sure there is something to read */
	if (bytes_avail_toread < buflen) {
	spin_unlock_irqrestore(&inring_info->ring_lock, flags);

	return -EAGAIN;
	}

	next_read_location =
	hv_get_next_readlocation_withoffset(inring_info, offset);

	next_read_location = hv_copyfrom_ringbuffer(inring_info,
	buffer,
	buflen,
	next_read_location);

	next_read_location = hv_copyfrom_ringbuffer(inring_info,
	&prev_indices,
	sizeof(u64),
	next_read_location);

	/* 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 /
	smp_mb();

	/* Update the read index */
	hv_set_next_read_location(inring_info, next_read_location);

	spin_unlock_irqrestore(&inring_info->ring_lock, flags);

	return 0;
	}