drivers/media/dvb-core/dvb_ringbuffer.c - linux - Git at Google

 /*
  *
  * dvb_ringbuffer.c: ring buffer implementation for the dvb driver
  *
  * Copyright (C) 2003 Oliver Endriss
  * Copyright (C) 2004 Andrew de Quincey
  *
  * based on code originally found in av7110.c & dvb_ci.c:
  * Copyright (C) 1999-2003 Ralph  Metzler
  *                       & Marcus Metzler for convergence integrated media GmbH
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
  * as published by the Free Software Foundation; either version 2.1
  * of the License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU Lesser General Public License for more details.
  */


 #include <linux/errno.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/string.h>
 #include <linux/uaccess.h>

 #include <media/dvb_ringbuffer.h>

 #define PKT_READY 0
 #define PKT_DISPOSED 1


 void dvb_ringbuffer_init(struct dvb_ringbuffer *rbuf, void *data, size_t len)
 {
 	rbuf->pread=rbuf->pwrite=0;
 	rbuf->data=data;
 	rbuf->size=len;
 	rbuf->error=0;

 	init_waitqueue_head(&rbuf->queue);

 	spin_lock_init(&(rbuf->lock));
 }


 int dvb_ringbuffer_empty(struct dvb_ringbuffer *rbuf)
 {
 	/* smp_load_acquire() to load write pointer on reader side
 	 * this pairs with smp_store_release() in dvb_ringbuffer_write(),
 	 * dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset()
 	 *
 	 * for memory barriers also see Documentation/core-api/circular-buffers.rst
 	 */
 	return (rbuf->pread == smp_load_acquire(&rbuf->pwrite));
 }


 ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf)
 {
 	ssize_t free;

 	/* READ_ONCE() to load read pointer on writer side
 	 * this pairs with smp_store_release() in dvb_ringbuffer_read(),
 	 * dvb_ringbuffer_read_user(), dvb_ringbuffer_flush(),
 	 * or dvb_ringbuffer_reset()
 	 */
 	free = READ_ONCE(rbuf->pread) - rbuf->pwrite;
 	if (free <= 0)
 		free += rbuf->size;
 	return free-1;
 }


 ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf)
 {
 	ssize_t avail;

 	/* smp_load_acquire() to load write pointer on reader side
 	 * this pairs with smp_store_release() in dvb_ringbuffer_write(),
 	 * dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset()
 	 */
 	avail = smp_load_acquire(&rbuf->pwrite) - rbuf->pread;
 	if (avail < 0)
 		avail += rbuf->size;
 	return avail;
 }


 void dvb_ringbuffer_flush(struct dvb_ringbuffer *rbuf)
 {
 	/* dvb_ringbuffer_flush() counts as read operation
 	 * smp_load_acquire() to load write pointer
 	 * smp_store_release() to update read pointer, this ensures that the
 	 * correct pointer is visible for subsequent dvb_ringbuffer_free()
 	 * calls on other cpu cores
 	 */
 	smp_store_release(&rbuf->pread, smp_load_acquire(&rbuf->pwrite));
 	rbuf->error = 0;
 }
 EXPORT_SYMBOL(dvb_ringbuffer_flush);

 void dvb_ringbuffer_reset(struct dvb_ringbuffer *rbuf)
 {
 	/* dvb_ringbuffer_reset() counts as read and write operation
 	 * smp_store_release() to update read pointer
 	 */
 	smp_store_release(&rbuf->pread, 0);
 	/* smp_store_release() to update write pointer */
 	smp_store_release(&rbuf->pwrite, 0);
 	rbuf->error = 0;
 }

 void dvb_ringbuffer_flush_spinlock_wakeup(struct dvb_ringbuffer *rbuf)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&rbuf->lock, flags);
 	dvb_ringbuffer_flush(rbuf);
 	spin_unlock_irqrestore(&rbuf->lock, flags);

 	wake_up(&rbuf->queue);
 }

 ssize_t dvb_ringbuffer_read_user(struct dvb_ringbuffer *rbuf, u8 __user *buf, size_t len)
 {
 	size_t todo = len;
 	size_t split;

 	split = (rbuf->pread + len > rbuf->size) ? rbuf->size - rbuf->pread : 0;
 	if (split > 0) {
 		if (copy_to_user(buf, rbuf->data+rbuf->pread, split))
 			return -EFAULT;
 		buf += split;
 		todo -= split;
 		/* smp_store_release() for read pointer update to ensure
 		 * that buf is not overwritten until read is complete,
 		 * this pairs with READ_ONCE() in dvb_ringbuffer_free()
 		 */
 		smp_store_release(&rbuf->pread, 0);
 	}
 	if (copy_to_user(buf, rbuf->data+rbuf->pread, todo))
 		return -EFAULT;

 	/* smp_store_release() to update read pointer, see above */
 	smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);

 	return len;
 }

 void dvb_ringbuffer_read(struct dvb_ringbuffer *rbuf, u8 *buf, size_t len)
 {
 	size_t todo = len;
 	size_t split;

 	split = (rbuf->pread + len > rbuf->size) ? rbuf->size - rbuf->pread : 0;
 	if (split > 0) {
 		memcpy(buf, rbuf->data+rbuf->pread, split);
 		buf += split;
 		todo -= split;
 		/* smp_store_release() for read pointer update to ensure
 		 * that buf is not overwritten until read is complete,
 		 * this pairs with READ_ONCE() in dvb_ringbuffer_free()
 		 */
 		smp_store_release(&rbuf->pread, 0);
 	}
 	memcpy(buf, rbuf->data+rbuf->pread, todo);

 	/* smp_store_release() to update read pointer, see above */
 	smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);
 }


 ssize_t dvb_ringbuffer_write(struct dvb_ringbuffer *rbuf, const u8 *buf, size_t len)
 {
 	size_t todo = len;
 	size_t split;

 	split = (rbuf->pwrite + len > rbuf->size) ? rbuf->size - rbuf->pwrite : 0;

 	if (split > 0) {
 		memcpy(rbuf->data+rbuf->pwrite, buf, split);
 		buf += split;
 		todo -= split;
 		/* smp_store_release() for write pointer update to ensure that
 		 * written data is visible on other cpu cores before the pointer
 		 * update, this pairs with smp_load_acquire() in
 		 * dvb_ringbuffer_empty() or dvb_ringbuffer_avail()
 		 */
 		smp_store_release(&rbuf->pwrite, 0);
 	}
 	memcpy(rbuf->data+rbuf->pwrite, buf, todo);
 	/* smp_store_release() for write pointer update, see above */
 	smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);

 	return len;
 }

 ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer *rbuf,
 				  const u8 __user *buf, size_t len)
 {
 	int status;
 	size_t todo = len;
 	size_t split;

 	split = (rbuf->pwrite + len > rbuf->size) ? rbuf->size - rbuf->pwrite : 0;

 	if (split > 0) {
 		status = copy_from_user(rbuf->data+rbuf->pwrite, buf, split);
 		if (status)
 			return len - todo;
 		buf += split;
 		todo -= split;
 		/* smp_store_release() for write pointer update to ensure that
 		 * written data is visible on other cpu cores before the pointer
 		 * update, this pairs with smp_load_acquire() in
 		 * dvb_ringbuffer_empty() or dvb_ringbuffer_avail()
 		 */
 		smp_store_release(&rbuf->pwrite, 0);
 	}
 	status = copy_from_user(rbuf->data+rbuf->pwrite, buf, todo);
 	if (status)
 		return len - todo;
 	/* smp_store_release() for write pointer update, see above */
 	smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);

 	return len;
 }

 ssize_t dvb_ringbuffer_pkt_write(struct dvb_ringbuffer *rbuf, u8* buf, size_t len)
 {
 	int status;
 	ssize_t oldpwrite = rbuf->pwrite;

 	DVB_RINGBUFFER_WRITE_BYTE(rbuf, len >> 8);
 	DVB_RINGBUFFER_WRITE_BYTE(rbuf, len & 0xff);
 	DVB_RINGBUFFER_WRITE_BYTE(rbuf, PKT_READY);
 	status = dvb_ringbuffer_write(rbuf, buf, len);

 	if (status < 0) rbuf->pwrite = oldpwrite;
 	return status;
 }

 ssize_t dvb_ringbuffer_pkt_read_user(struct dvb_ringbuffer *rbuf, size_t idx,
 				int offset, u8 __user *buf, size_t len)
 {
 	size_t todo;
 	size_t split;
 	size_t pktlen;

 	pktlen = rbuf->data[idx] << 8;
 	pktlen |= rbuf->data[(idx + 1) % rbuf->size];
 	if (offset > pktlen) return -EINVAL;
 	if ((offset + len) > pktlen) len = pktlen - offset;

 	idx = (idx + DVB_RINGBUFFER_PKTHDRSIZE + offset) % rbuf->size;
 	todo = len;
 	split = ((idx + len) > rbuf->size) ? rbuf->size - idx : 0;
 	if (split > 0) {
 		if (copy_to_user(buf, rbuf->data+idx, split))
 			return -EFAULT;
 		buf += split;
 		todo -= split;
 		idx = 0;
 	}
 	if (copy_to_user(buf, rbuf->data+idx, todo))
 		return -EFAULT;

 	return len;
 }

 ssize_t dvb_ringbuffer_pkt_read(struct dvb_ringbuffer *rbuf, size_t idx,
 				int offset, u8* buf, size_t len)
 {
 	size_t todo;
 	size_t split;
 	size_t pktlen;

 	pktlen = rbuf->data[idx] << 8;
 	pktlen |= rbuf->data[(idx + 1) % rbuf->size];
 	if (offset > pktlen) return -EINVAL;
 	if ((offset + len) > pktlen) len = pktlen - offset;

 	idx = (idx + DVB_RINGBUFFER_PKTHDRSIZE + offset) % rbuf->size;
 	todo = len;
 	split = ((idx + len) > rbuf->size) ? rbuf->size - idx : 0;
 	if (split > 0) {
 		memcpy(buf, rbuf->data+idx, split);
 		buf += split;
 		todo -= split;
 		idx = 0;
 	}
 	memcpy(buf, rbuf->data+idx, todo);
 	return len;
 }

 void dvb_ringbuffer_pkt_dispose(struct dvb_ringbuffer *rbuf, size_t idx)
 {
 	size_t pktlen;

 	rbuf->data[(idx + 2) % rbuf->size] = PKT_DISPOSED;

 	// clean up disposed packets
 	while(dvb_ringbuffer_avail(rbuf) > DVB_RINGBUFFER_PKTHDRSIZE) {
 		if (DVB_RINGBUFFER_PEEK(rbuf, 2) == PKT_DISPOSED) {
 			pktlen = DVB_RINGBUFFER_PEEK(rbuf, 0) << 8;
 			pktlen |= DVB_RINGBUFFER_PEEK(rbuf, 1);
 			DVB_RINGBUFFER_SKIP(rbuf, pktlen + DVB_RINGBUFFER_PKTHDRSIZE);
 		} else {
 			// first packet is not disposed, so we stop cleaning now
 			break;
 		}
 	}
 }

 ssize_t dvb_ringbuffer_pkt_next(struct dvb_ringbuffer *rbuf, size_t idx, size_t* pktlen)
 {
 	int consumed;
 	int curpktlen;
 	int curpktstatus;

 	if (idx == -1) {
 	       idx = rbuf->pread;
 	} else {
 		curpktlen = rbuf->data[idx] << 8;
 		curpktlen |= rbuf->data[(idx + 1) % rbuf->size];
 		idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
 	}

 	consumed = (idx - rbuf->pread);
 	if (consumed < 0)
 		consumed += rbuf->size;

 	while((dvb_ringbuffer_avail(rbuf) - consumed) > DVB_RINGBUFFER_PKTHDRSIZE) {

 		curpktlen = rbuf->data[idx] << 8;
 		curpktlen |= rbuf->data[(idx + 1) % rbuf->size];
 		curpktstatus = rbuf->data[(idx + 2) % rbuf->size];

 		if (curpktstatus == PKT_READY) {
 			*pktlen = curpktlen;
 			return idx;
 		}

 		consumed += curpktlen + DVB_RINGBUFFER_PKTHDRSIZE;
 		idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
 	}

 	// no packets available
 	return -1;
 }


 EXPORT_SYMBOL(dvb_ringbuffer_init);
 EXPORT_SYMBOL(dvb_ringbuffer_empty);
 EXPORT_SYMBOL(dvb_ringbuffer_free);
 EXPORT_SYMBOL(dvb_ringbuffer_avail);
 EXPORT_SYMBOL(dvb_ringbuffer_flush_spinlock_wakeup);
 EXPORT_SYMBOL(dvb_ringbuffer_read_user);
 EXPORT_SYMBOL(dvb_ringbuffer_read);
 EXPORT_SYMBOL(dvb_ringbuffer_write);
 EXPORT_SYMBOL(dvb_ringbuffer_write_user);
	/*
	*
	* dvb_ringbuffer.c: ring buffer implementation for the dvb driver
	*
	* Copyright (C) 2003 Oliver Endriss
	* Copyright (C) 2004 Andrew de Quincey
	*
	* based on code originally found in av7110.c & dvb_ci.c:
	* Copyright (C) 1999-2003 Ralph Metzler
	* & Marcus Metzler for convergence integrated media GmbH
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public License
	* as published by the Free Software Foundation; either version 2.1
	* of the License, or (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU Lesser General Public License for more details.
	*/



	#include <linux/errno.h>
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/string.h>
	#include <linux/uaccess.h>

	#include <media/dvb_ringbuffer.h>

	#define PKT_READY 0
	#define PKT_DISPOSED 1


	void dvb_ringbuffer_init(struct dvb_ringbuffer rbuf, void data, size_t len)
	{
	rbuf->pread=rbuf->pwrite=0;
	rbuf->data=data;
	rbuf->size=len;
	rbuf->error=0;

	init_waitqueue_head(&rbuf->queue);

	spin_lock_init(&(rbuf->lock));
	}



	int dvb_ringbuffer_empty(struct dvb_ringbuffer *rbuf)
	{
	/* smp_load_acquire() to load write pointer on reader side
	* this pairs with smp_store_release() in dvb_ringbuffer_write(),
	* dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset()
	*
	* for memory barriers also see Documentation/core-api/circular-buffers.rst
	*/
	return (rbuf->pread == smp_load_acquire(&rbuf->pwrite));
	}



	ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf)
	{
	ssize_t free;

	/* READ_ONCE() to load read pointer on writer side
	* this pairs with smp_store_release() in dvb_ringbuffer_read(),
	* dvb_ringbuffer_read_user(), dvb_ringbuffer_flush(),
	* or dvb_ringbuffer_reset()
	*/
	free = READ_ONCE(rbuf->pread) - rbuf->pwrite;
	if (free <= 0)
	free += rbuf->size;
	return free-1;
	}



	ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf)
	{
	ssize_t avail;

	/* smp_load_acquire() to load write pointer on reader side
	* this pairs with smp_store_release() in dvb_ringbuffer_write(),
	* dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset()
	*/
	avail = smp_load_acquire(&rbuf->pwrite) - rbuf->pread;
	if (avail < 0)
	avail += rbuf->size;
	return avail;
	}



	void dvb_ringbuffer_flush(struct dvb_ringbuffer *rbuf)
	{
	/* dvb_ringbuffer_flush() counts as read operation
	* smp_load_acquire() to load write pointer
	* smp_store_release() to update read pointer, this ensures that the
	* correct pointer is visible for subsequent dvb_ringbuffer_free()
	* calls on other cpu cores
	*/
	smp_store_release(&rbuf->pread, smp_load_acquire(&rbuf->pwrite));
	rbuf->error = 0;
	}
	EXPORT_SYMBOL(dvb_ringbuffer_flush);

	void dvb_ringbuffer_reset(struct dvb_ringbuffer *rbuf)
	{
	/* dvb_ringbuffer_reset() counts as read and write operation
	* smp_store_release() to update read pointer
	*/
	smp_store_release(&rbuf->pread, 0);
	/* smp_store_release() to update write pointer */
	smp_store_release(&rbuf->pwrite, 0);
	rbuf->error = 0;
	}

	void dvb_ringbuffer_flush_spinlock_wakeup(struct dvb_ringbuffer *rbuf)
	{
	unsigned long flags;

	spin_lock_irqsave(&rbuf->lock, flags);
	dvb_ringbuffer_flush(rbuf);
	spin_unlock_irqrestore(&rbuf->lock, flags);

	wake_up(&rbuf->queue);
	}

	ssize_t dvb_ringbuffer_read_user(struct dvb_ringbuffer rbuf, u8 __user buf, size_t len)
	{
	size_t todo = len;
	size_t split;

	split = (rbuf->pread + len > rbuf->size) ? rbuf->size - rbuf->pread : 0;
	if (split > 0) {
	if (copy_to_user(buf, rbuf->data+rbuf->pread, split))
	return -EFAULT;
	buf += split;
	todo -= split;
	/* smp_store_release() for read pointer update to ensure
	* that buf is not overwritten until read is complete,
	* this pairs with READ_ONCE() in dvb_ringbuffer_free()
	*/
	smp_store_release(&rbuf->pread, 0);
	}
	if (copy_to_user(buf, rbuf->data+rbuf->pread, todo))
	return -EFAULT;

	/* smp_store_release() to update read pointer, see above */
	smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);

	return len;
	}

	void dvb_ringbuffer_read(struct dvb_ringbuffer rbuf, u8 buf, size_t len)
	{
	size_t todo = len;
	size_t split;

	split = (rbuf->pread + len > rbuf->size) ? rbuf->size - rbuf->pread : 0;
	if (split > 0) {
	memcpy(buf, rbuf->data+rbuf->pread, split);
	buf += split;
	todo -= split;
	/* smp_store_release() for read pointer update to ensure
	* that buf is not overwritten until read is complete,
	* this pairs with READ_ONCE() in dvb_ringbuffer_free()
	*/
	smp_store_release(&rbuf->pread, 0);
	}
	memcpy(buf, rbuf->data+rbuf->pread, todo);

	/* smp_store_release() to update read pointer, see above */
	smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);
	}


	ssize_t dvb_ringbuffer_write(struct dvb_ringbuffer rbuf, const u8 buf, size_t len)
	{
	size_t todo = len;
	size_t split;

	split = (rbuf->pwrite + len > rbuf->size) ? rbuf->size - rbuf->pwrite : 0;

	if (split > 0) {
	memcpy(rbuf->data+rbuf->pwrite, buf, split);
	buf += split;
	todo -= split;
	/* smp_store_release() for write pointer update to ensure that
	* written data is visible on other cpu cores before the pointer
	* update, this pairs with smp_load_acquire() in
	* dvb_ringbuffer_empty() or dvb_ringbuffer_avail()
	*/
	smp_store_release(&rbuf->pwrite, 0);
	}
	memcpy(rbuf->data+rbuf->pwrite, buf, todo);
	/* smp_store_release() for write pointer update, see above */
	smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);

	return len;
	}

	ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer *rbuf,
	const u8 __user *buf, size_t len)
	{
	int status;
	size_t todo = len;
	size_t split;

	split = (rbuf->pwrite + len > rbuf->size) ? rbuf->size - rbuf->pwrite : 0;

	if (split > 0) {
	status = copy_from_user(rbuf->data+rbuf->pwrite, buf, split);
	if (status)
	return len - todo;
	buf += split;
	todo -= split;
	/* smp_store_release() for write pointer update to ensure that
	* written data is visible on other cpu cores before the pointer
	* update, this pairs with smp_load_acquire() in
	* dvb_ringbuffer_empty() or dvb_ringbuffer_avail()
	*/
	smp_store_release(&rbuf->pwrite, 0);
	}
	status = copy_from_user(rbuf->data+rbuf->pwrite, buf, todo);
	if (status)
	return len - todo;
	/* smp_store_release() for write pointer update, see above */
	smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);

	return len;
	}

	ssize_t dvb_ringbuffer_pkt_write(struct dvb_ringbuffer rbuf, u8 buf, size_t len)
	{
	int status;
	ssize_t oldpwrite = rbuf->pwrite;

	DVB_RINGBUFFER_WRITE_BYTE(rbuf, len >> 8);
	DVB_RINGBUFFER_WRITE_BYTE(rbuf, len & 0xff);
	DVB_RINGBUFFER_WRITE_BYTE(rbuf, PKT_READY);
	status = dvb_ringbuffer_write(rbuf, buf, len);

	if (status < 0) rbuf->pwrite = oldpwrite;
	return status;
	}

	ssize_t dvb_ringbuffer_pkt_read_user(struct dvb_ringbuffer *rbuf, size_t idx,
	int offset, u8 __user *buf, size_t len)
	{
	size_t todo;
	size_t split;
	size_t pktlen;

	pktlen = rbuf->data[idx] << 8;
	pktlen \|= rbuf->data[(idx + 1) % rbuf->size];
	if (offset > pktlen) return -EINVAL;
	if ((offset + len) > pktlen) len = pktlen - offset;

	idx = (idx + DVB_RINGBUFFER_PKTHDRSIZE + offset) % rbuf->size;
	todo = len;
	split = ((idx + len) > rbuf->size) ? rbuf->size - idx : 0;
	if (split > 0) {
	if (copy_to_user(buf, rbuf->data+idx, split))
	return -EFAULT;
	buf += split;
	todo -= split;
	idx = 0;
	}
	if (copy_to_user(buf, rbuf->data+idx, todo))
	return -EFAULT;

	return len;
	}

	ssize_t dvb_ringbuffer_pkt_read(struct dvb_ringbuffer *rbuf, size_t idx,
	int offset, u8* buf, size_t len)
	{
	size_t todo;
	size_t split;
	size_t pktlen;

	pktlen = rbuf->data[idx] << 8;
	pktlen \|= rbuf->data[(idx + 1) % rbuf->size];
	if (offset > pktlen) return -EINVAL;
	if ((offset + len) > pktlen) len = pktlen - offset;

	idx = (idx + DVB_RINGBUFFER_PKTHDRSIZE + offset) % rbuf->size;
	todo = len;
	split = ((idx + len) > rbuf->size) ? rbuf->size - idx : 0;
	if (split > 0) {
	memcpy(buf, rbuf->data+idx, split);
	buf += split;
	todo -= split;
	idx = 0;
	}
	memcpy(buf, rbuf->data+idx, todo);
	return len;
	}

	void dvb_ringbuffer_pkt_dispose(struct dvb_ringbuffer *rbuf, size_t idx)
	{
	size_t pktlen;

	rbuf->data[(idx + 2) % rbuf->size] = PKT_DISPOSED;

	// clean up disposed packets
	while(dvb_ringbuffer_avail(rbuf) > DVB_RINGBUFFER_PKTHDRSIZE) {
	if (DVB_RINGBUFFER_PEEK(rbuf, 2) == PKT_DISPOSED) {
	pktlen = DVB_RINGBUFFER_PEEK(rbuf, 0) << 8;
	pktlen \|= DVB_RINGBUFFER_PEEK(rbuf, 1);
	DVB_RINGBUFFER_SKIP(rbuf, pktlen + DVB_RINGBUFFER_PKTHDRSIZE);
	} else {
	// first packet is not disposed, so we stop cleaning now
	break;
	}
	}
	}

	ssize_t dvb_ringbuffer_pkt_next(struct dvb_ringbuffer rbuf, size_t idx, size_t pktlen)
	{
	int consumed;
	int curpktlen;
	int curpktstatus;

	if (idx == -1) {
	idx = rbuf->pread;
	} else {
	curpktlen = rbuf->data[idx] << 8;
	curpktlen \|= rbuf->data[(idx + 1) % rbuf->size];
	idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
	}

	consumed = (idx - rbuf->pread);
	if (consumed < 0)
	consumed += rbuf->size;

	while((dvb_ringbuffer_avail(rbuf) - consumed) > DVB_RINGBUFFER_PKTHDRSIZE) {

	curpktlen = rbuf->data[idx] << 8;
	curpktlen \|= rbuf->data[(idx + 1) % rbuf->size];
	curpktstatus = rbuf->data[(idx + 2) % rbuf->size];

	if (curpktstatus == PKT_READY) {
	*pktlen = curpktlen;
	return idx;
	}

	consumed += curpktlen + DVB_RINGBUFFER_PKTHDRSIZE;
	idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
	}

	// no packets available
	return -1;
	}



	EXPORT_SYMBOL(dvb_ringbuffer_init);
	EXPORT_SYMBOL(dvb_ringbuffer_empty);
	EXPORT_SYMBOL(dvb_ringbuffer_free);
	EXPORT_SYMBOL(dvb_ringbuffer_avail);
	EXPORT_SYMBOL(dvb_ringbuffer_flush_spinlock_wakeup);
	EXPORT_SYMBOL(dvb_ringbuffer_read_user);
	EXPORT_SYMBOL(dvb_ringbuffer_read);
	EXPORT_SYMBOL(dvb_ringbuffer_write);
	EXPORT_SYMBOL(dvb_ringbuffer_write_user);