Packet buffers (PBUF)

Enumerations
enum	pbuf_layer {   PBUF_TRANSPORT, PBUF_IP, PBUF_LINK, PBUF_RAW_TX,   PBUF_RAW }
enum	pbuf_type { PBUF_RAM, PBUF_ROM, PBUF_REF, PBUF_POOL }

Functions
struct pbuf *	pbuf_alloc (pbuf_layer layer, u16_t length, pbuf_type type)
struct pbuf *	pbuf_alloced_custom (pbuf_layer l, u16_t length, pbuf_type type, struct pbuf_custom *p, void *payload_mem, u16_t payload_mem_len)
void	pbuf_realloc (struct pbuf *p, u16_t new_len)
u8_t	pbuf_free (struct pbuf *p)
void	pbuf_ref (struct pbuf *p)
void	pbuf_cat (struct pbuf *h, struct pbuf *t)
void	pbuf_chain (struct pbuf *h, struct pbuf *t)
err_t	pbuf_copy (struct pbuf *p_to, const struct pbuf *p_from)
u16_t	pbuf_copy_partial (const struct pbuf *buf, void *dataptr, u16_t len, u16_t offset)
struct pbuf *	pbuf_skip (struct pbuf *in, u16_t in_offset, u16_t *out_offset)
err_t	pbuf_take (struct pbuf *buf, const void *dataptr, u16_t len)
err_t	pbuf_take_at (struct pbuf *buf, const void *dataptr, u16_t len, u16_t offset)
struct pbuf *	pbuf_coalesce (struct pbuf *p, pbuf_layer layer)
u8_t	pbuf_get_at (const struct pbuf *p, u16_t offset)
int	pbuf_try_get_at (const struct pbuf *p, u16_t offset)
void	pbuf_put_at (struct pbuf *p, u16_t offset, u8_t data)
u16_t	pbuf_memcmp (const struct pbuf *p, u16_t offset, const void *s2, u16_t n)
u16_t	pbuf_memfind (const struct pbuf *p, const void *mem, u16_t mem_len, u16_t start_offset)

Detailed Description

Packets are built from the pbuf data structure. It supports dynamic memory allocation for packet contents or can reference externally managed packet contents both in RAM and ROM. Quick allocation for incoming packets is provided through pools with fixed sized pbufs.

A packet may span over multiple pbufs, chained as a singly linked list. This is called a "pbuf chain".

Multiple packets may be queued, also using this singly linked list. This is called a "packet queue".

So, a packet queue consists of one or more pbuf chains, each of which consist of one or more pbufs. CURRENTLY, PACKET QUEUES ARE NOT SUPPORTED!!! Use helper structs to queue multiple packets.

The differences between a pbuf chain and a packet queue are very precise but subtle.

The last pbuf of a packet has a ->tot_len field that equals the ->len field. It can be found by traversing the list. If the last pbuf of a packet has a ->next field other than NULL, more packets are on the queue.

Therefore, looping through a pbuf of a single packet, has an loop end condition (tot_len == p->len), NOT (next == NULL).

Example of custom pbuf usage for zero-copy RX:

typedef struct my_custom_pbuf
{
   struct pbuf_custom p;
   void* dma_descriptor;
} my_custom_pbuf_t;

LWIP_MEMPOOL_DECLARE(RX_POOL, 10, sizeof(my_custom_pbuf_t), "Zero-copy RX PBUF pool");

void my_pbuf_free_custom(void* p)
{
  my_custom_pbuf_t* my_puf = (my_custom_pbuf_t*)p;

  LOCK_INTERRUPTS();
  free_rx_dma_descriptor(my_pbuf->dma_descriptor);
  LWIP_MEMPOOL_FREE(RX_POOL, my_pbuf);
  UNLOCK_INTERRUPTS();
}

void eth_rx_irq()
{
  dma_descriptor*   dma_desc = get_RX_DMA_descriptor_from_ethernet();
  my_custom_pbuf_t* my_pbuf  = (my_custom_pbuf_t*)LWIP_MEMPOOL_ALLOC(RX_POOL);

  my_pbuf->p.custom_free_function = my_pbuf_free_custom;
  my_pbuf->dma_descriptor         = dma_desc;

  invalidate_cpu_cache(dma_desc->rx_data, dma_desc->rx_length);
  
  struct pbuf* p = pbuf_alloced_custom(PBUF_RAW,
     dma_desc->rx_length,
     PBUF_REF,
     &my_pbuf->p,
     dma_desc->rx_data,
     dma_desc->max_buffer_size);

  if(netif->input(p, netif) != ERR_OK) {
    pbuf_free(p);
  }
}

Enumeration Type Documentation

pbuf_layer

enum pbuf_layer

Enumeration of pbuf layers

Enumerator
PBUF_TRANSPORT	Includes spare room for transport layer header, e.g. UDP header. Use this if you intend to pass the pbuf to functions like udp_send().
PBUF_IP	Includes spare room for IP header. Use this if you intend to pass the pbuf to functions like raw_send().
PBUF_LINK	Includes spare room for link layer header (ethernet header). Use this if you intend to pass the pbuf to functions like ethernet_output(). See also PBUF_LINK_HLEN
PBUF_RAW_TX	Includes spare room for additional encapsulation header before ethernet headers (e.g. 802.11). Use this if you intend to pass the pbuf to functions like netif->linkoutput(). See also PBUF_LINK_ENCAPSULATION_HLEN
PBUF_RAW	Use this for input packets in a netif driver when calling netif->input() in the most common case - ethernet-layer netif driver.

pbuf_type

enum pbuf_type

Enumeration of pbuf types

Enumerator
PBUF_RAM	pbuf data is stored in RAM, used for TX mostly, struct pbuf and its payload are allocated in one piece of contiguous memory (so the first payload byte can be calculated from struct pbuf). pbuf_alloc() allocates PBUF_RAM pbufs as unchained pbufs (although that might change in future versions). This should be used for all OUTGOING packets (TX).
PBUF_ROM	pbuf data is stored in ROM, i.e. struct pbuf and its payload are located in totally different memory areas. Since it points to ROM, payload does not have to be copied when queued for transmission.
PBUF_REF	pbuf comes from the pbuf pool. Much like PBUF_ROM but payload might change so it has to be duplicated when queued before transmitting, depending on who has a 'ref' to it.
PBUF_POOL	pbuf payload refers to RAM. This one comes from a pool and should be used for RX. Payload can be chained (scatter-gather RX) but like PBUF_RAM, struct pbuf and its payload are allocated in one piece of contiguous memory (so the first payload byte can be calculated from struct pbuf). Don't use this for TX, if the pool becomes empty e.g. because of TCP queuing, you are unable to receive TCP acks!

Function Documentation

pbuf_alloc()

struct pbuf* pbuf_alloc	(	pbuf_layer	layer,
		u16_t	length,
		pbuf_type	type
	)

Allocates a pbuf of the given type (possibly a chain for PBUF_POOL type).

The actual memory allocated for the pbuf is determined by the layer at which the pbuf is allocated and the requested size (from the size parameter).

Parameters

layer	flag to define header size
length	size of the pbuf's payload
type	this parameter decides how and where the pbuf should be allocated as follows:

• PBUF_RAM: buffer memory for pbuf is allocated as one large chunk. This includes protocol headers as well.
• PBUF_ROM: no buffer memory is allocated for the pbuf, even for protocol headers. Additional headers must be prepended by allocating another pbuf and chain in to the front of the ROM pbuf. It is assumed that the memory used is really similar to ROM in that it is immutable and will not be changed. Memory which is dynamic should generally not be attached to PBUF_ROM pbufs. Use PBUF_REF instead.
• PBUF_REF: no buffer memory is allocated for the pbuf, even for protocol headers. It is assumed that the pbuf is only being used in a single thread. If the pbuf gets queued, then pbuf_take should be called to copy the buffer.
• PBUF_POOL: the pbuf is allocated as a pbuf chain, with pbufs from the pbuf pool that is allocated during pbuf_init().

Returns

the allocated pbuf. If multiple pbufs where allocated, this is the first pbuf of a pbuf chain.

pbuf_alloced_custom()

struct pbuf* pbuf_alloced_custom	(	pbuf_layer	l,
		u16_t	length,
		pbuf_type	type,
		struct pbuf_custom *	p,
		void *	payload_mem,
		u16_t	payload_mem_len
	)

Initialize a custom pbuf (already allocated).

Parameters

l	flag to define header size
length	size of the pbuf's payload
type	type of the pbuf (only used to treat the pbuf accordingly, as this function allocates no memory)
p	pointer to the custom pbuf to initialize (already allocated)
payload_mem	pointer to the buffer that is used for payload and headers, must be at least big enough to hold 'length' plus the header size, may be NULL if set later. ATTENTION: The caller is responsible for correct alignment of this buffer!!
payload_mem_len	the size of the 'payload_mem' buffer, must be at least big enough to hold 'length' plus the header size

pbuf_cat()

void pbuf_cat	(	struct pbuf *	h,
		struct pbuf *	t
	)

Concatenate two pbufs (each may be a pbuf chain) and take over the caller's reference of the tail pbuf.

Note

The caller MAY NOT reference the tail pbuf afterwards. Use pbuf_chain() for that purpose.

See also

pbuf_chain()

pbuf_chain()

void pbuf_chain	(	struct pbuf *	h,
		struct pbuf *	t
	)

Chain two pbufs (or pbuf chains) together.

The caller MUST call pbuf_free(t) once it has stopped using it. Use pbuf_cat() instead if you no longer use t.

Parameters

h	head pbuf (chain)
t	tail pbuf (chain)

Note

The pbufs MUST belong to the same packet.

MAY NOT be called on a packet queue.

The ->tot_len fields of all pbufs of the head chain are adjusted. The ->next field of the last pbuf of the head chain is adjusted. The ->ref field of the first pbuf of the tail chain is adjusted.

pbuf_coalesce()

struct pbuf* pbuf_coalesce	(	struct pbuf *	p,
		pbuf_layer	layer
	)

Creates a single pbuf out of a queue of pbufs.

Remarks

: Either the source pbuf 'p' is freed by this function or the original pbuf 'p' is returned, therefore the caller has to check the result!

Parameters

p	the source pbuf
layer	pbuf_layer of the new pbuf

Returns

a new, single pbuf (p->next is NULL) or the old pbuf if allocation fails

pbuf_copy()

err_t pbuf_copy	(	struct pbuf *	p_to,
		const struct pbuf *	p_from
	)

Create PBUF_RAM copies of pbufs.

Used to queue packets on behalf of the lwIP stack, such as ARP based queueing.

Note

You MUST explicitly use p = pbuf_take(p);

Only one packet is copied, no packet queue!

Parameters

p_to	pbuf destination of the copy
p_from	pbuf source of the copy

Returns

ERR_OK if pbuf was copied ERR_ARG if one of the pbufs is NULL or p_to is not big enough to hold p_from

pbuf_copy_partial()

u16_t pbuf_copy_partial	(	const struct pbuf *	buf,
		void *	dataptr,
		u16_t	len,
		u16_t	offset
	)

Copy (part of) the contents of a packet buffer to an application supplied buffer.

Parameters

buf	the pbuf from which to copy data
dataptr	the application supplied buffer
len	length of data to copy (dataptr must be big enough). No more than buf->tot_len will be copied, irrespective of len
offset	offset into the packet buffer from where to begin copying len bytes

Returns

the number of bytes copied, or 0 on failure

pbuf_free()

u8_t pbuf_free

(

struct pbuf *

p

)

Dereference a pbuf chain or queue and deallocate any no-longer-used pbufs at the head of this chain or queue.

Decrements the pbuf reference count. If it reaches zero, the pbuf is deallocated.

For a pbuf chain, this is repeated for each pbuf in the chain, up to the first pbuf which has a non-zero reference count after decrementing. So, when all reference counts are one, the whole chain is free'd.

Parameters

p	The pbuf (chain) to be dereferenced.

Returns

the number of pbufs that were de-allocated from the head of the chain.

Note

MUST NOT be called on a packet queue (Not verified to work yet).

the reference counter of a pbuf equals the number of pointers that refer to the pbuf (or into the pbuf).

pbuf_get_at()

u8_t pbuf_get_at	(	const struct pbuf *	p,
		u16_t	offset
	)

Get one byte from the specified position in a pbuf WARNING: returns zero for offset >= p->tot_len

Parameters

p	pbuf to parse
offset	offset into p of the byte to return

Returns

byte at an offset into p OR ZERO IF 'offset' >= p->tot_len

pbuf_memcmp()

u16_t pbuf_memcmp	(	const struct pbuf *	p,
		u16_t	offset,
		const void *	s2,
		u16_t	n
	)

Compare pbuf contents at specified offset with memory s2, both of length n

Parameters

p	pbuf to compare
offset	offset into p at which to start comparing
s2	buffer to compare
n	length of buffer to compare

Returns

zero if equal, nonzero otherwise (0xffff if p is too short, diffoffset+1 otherwise)

pbuf_memfind()

u16_t pbuf_memfind	(	const struct pbuf *	p,
		const void *	mem,
		u16_t	mem_len,
		u16_t	start_offset
	)

Find occurrence of mem (with length mem_len) in pbuf p, starting at offset start_offset.

Parameters

p	pbuf to search, maximum length is 0xFFFE since 0xFFFF is used as return value 'not found'
mem	search for the contents of this buffer
mem_len	length of 'mem'
start_offset	offset into p at which to start searching

Returns

0xFFFF if substr was not found in p or the index where it was found

pbuf_put_at()

void pbuf_put_at	(	struct pbuf *	p,
		u16_t	offset,
		u8_t	data
	)

Put one byte to the specified position in a pbuf WARNING: silently ignores offset >= p->tot_len

Parameters

p	pbuf to fill
offset	offset into p of the byte to write
data	byte to write at an offset into p

pbuf_realloc()

void pbuf_realloc	(	struct pbuf *	p,
		u16_t	new_len
	)

Shrink a pbuf chain to a desired length.

Parameters

p	pbuf to shrink.
new_len	desired new length of pbuf chain

Depending on the desired length, the first few pbufs in a chain might be skipped and left unchanged. The new last pbuf in the chain will be resized, and any remaining pbufs will be freed.

Note

If the pbuf is ROM/REF, only the ->tot_len and ->len fields are adjusted.

May not be called on a packet queue.

Despite its name, pbuf_realloc cannot grow the size of a pbuf (chain).

pbuf_ref()

void pbuf_ref

(

struct pbuf *

p

)

Increment the reference count of the pbuf.

Parameters

p	pbuf to increase reference counter of

pbuf_skip()

struct pbuf* pbuf_skip	(	struct pbuf *	in,
		u16_t	in_offset,
		u16_t *	out_offset
	)

Skip a number of bytes at the start of a pbuf

Parameters

in	input pbuf
in_offset	offset to skip
out_offset	resulting offset in the returned pbuf

Returns

the pbuf in the queue where the offset is

pbuf_take()

err_t pbuf_take	(	struct pbuf *	buf,
		const void *	dataptr,
		u16_t	len
	)

Copy application supplied data into a pbuf. This function can only be used to copy the equivalent of buf->tot_len data.

Parameters

buf	pbuf to fill with data
dataptr	application supplied data buffer
len	length of the application supplied data buffer

Returns

ERR_OK if successful, ERR_MEM if the pbuf is not big enough

pbuf_take_at()

err_t pbuf_take_at	(	struct pbuf *	buf,
		const void *	dataptr,
		u16_t	len,
		u16_t	offset
	)

Same as pbuf_take() but puts data at an offset

Parameters

buf	pbuf to fill with data
dataptr	application supplied data buffer
len	length of the application supplied data buffer
offset	offset in pbuf where to copy dataptr to

Returns

ERR_OK if successful, ERR_MEM if the pbuf is not big enough

pbuf_try_get_at()

int pbuf_try_get_at	(	const struct pbuf *	p,
		u16_t	offset
	)

Get one byte from the specified position in a pbuf

Parameters

p	pbuf to parse
offset	offset into p of the byte to return

Returns

byte at an offset into p [0..0xFF] OR negative if 'offset' >= p->tot_len