<net/packetring.h>

Single-producer, single-consumer ring of Ethernet frames between a NIC driver and netd.

#include <net/packetring.h>

Constants

Name	Value	Description
NIC_FRAME_SIZE	1536	Bytes per frame slot.
NIC_RING_DEPTH	16	Slots per ring; one stays empty, so a ring holds NIC_RING_DEPTH - 1 frames.
NIC_MTU	1500	Largest IP packet in a frame.
NIC_RING_BYTES	sizeof(NicRing)	Size of one ring (24648 bytes).
NIC_RING_STRIDE		Ring size rounded up to whole pages (28672 bytes).
NIC_RX_OFFSET	0u	Offset of the rx ring in the shared memory.
NIC_TX_OFFSET	NIC_RING_STRIDE	Offset of the tx ring in the shared memory.
NIC_SHM_BYTES	(2u * NIC_RING_STRIDE)	Size of the shared memory: 14 pages.

Structures

NicFrame

One frame slot.

Field	Type	Description
len	uint32_t	Bytes of data in use.
data	uint8_t	Frame bytes.

NicRing

A ring of frames in shared memory; empty when head == tail.

Field	Type	Description
slots	NicFrame	Frame slots.
head	volatile uint32_t	Next slot the producer writes.
tail	volatile uint32_t	Next slot the consumer reads.

Functions

PacketRingPush

int PacketRingPush(NicRing *r, void *src, uint16_t len);

Producer: copies a frame into the ring.

Parameter	Direction	Description
r	inout	Ring.
src	in	Frame bytes.
len	in	Frame length, at most NIC_FRAME_SIZE.

Returns: 0, or an error code.

Error	Condition
ERR_OVERFLOW	r or src is NULL, or len is too large.
ERR_BUFFULL	The ring is full.

PacketRingPop

int PacketRingPop(NicFrame *dst, NicRing *r);

Consumer: copies the oldest frame out of the ring.

Parameter	Direction	Description
dst	out	Where to copy the frame.
r	inout	Ring.

Returns: 0, or an error code.

Error	Condition
ERR_BADARG	dst or r is NULL.
ERR_BUFEMPTY	The ring is empty.
ERR_OVERFLOW	The slot claimed an impossible length; it has been skipped.

PacketRingReserve

NicFrame * PacketRingReserve(NicRing *r);

Producer: returns the next free slot to fill in place, without copying.

Fill in its data and len, then call PacketRingCommit().

Parameter	Direction	Description
r	in	Ring.

Returns: The slot, or NULL if the ring is full or r is NULL.

PacketRingCommit

void PacketRingCommit(NicRing *r);

Producer: publishes the slot from PacketRingReserve().

A barrier orders the slot's contents before the new head.

Parameter	Direction	Description
r	inout	Ring.

PacketRingPeek

NicFrame * PacketRingPeek(NicRing *r);

Consumer: returns the oldest frame to read in place, without copying.

Call PacketRingConsume() when done with it.

Parameter	Direction	Description
r	in	Ring.

Returns: The slot, or NULL if the ring is empty or r is NULL.

PacketRingConsume

void PacketRingConsume(NicRing *r);

Consumer: releases the slot from PacketRingPeek() back to the producer.

Parameter	Direction	Description
r	inout	Ring.