pbuf.c File Reference

#include <string.h>
#include "lwip/opt.h"
#include "lwip/stats.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/pbuf.h"
#include "lwip/sys.h"
#include "arch/perf.h"

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Macros
#define	DEC_PBUF_STATS
#define	PBUF_POOL_FAST_FREE(p)
#define	PBUF_POOL_FREE(p)

Functions
void	pbuf_init (void)
static struct pbuf *	pbuf_pool_alloc (void)
struct pbuf *	pbuf_alloc (pbuf_layer l, u16_t length, pbuf_flag flag)
void	pbuf_realloc (struct pbuf *p, u16_t new_len)
u8_t	pbuf_header (struct pbuf *p, s16_t header_size_increment)
u8_t	pbuf_free (struct pbuf *p)
u8_t	pbuf_clen (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)
struct pbuf *	pbuf_take (struct pbuf *p)
struct pbuf *	pbuf_dechain (struct pbuf *p)

Variables
static u8_t	pbuf_pool_memory [MEM_ALIGNMENT - 1+PBUF_POOL_SIZE *MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE+sizeof(struct pbuf))]
static volatile u8_t	pbuf_pool_free_lock
static volatile u8_t	pbuf_pool_alloc_lock
static sys_sem	pbuf_pool_free_sem
static struct pbuf *	pbuf_pool = NULL

Detailed Description

Packet buffer management

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, queues are only supported in a limited section of lwIP, this is the etharp queueing code. Outside of this section no packet queues are supported yet.

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).

Macro Definition Documentation

DEC_PBUF_STATS

#define DEC_PBUF_STATS

PBUF_POOL_FAST_FREE

#define PBUF_POOL_FAST_FREE

(

p

)

Value:

do {                                    \
                                  p->next = pbuf_pool;                  \
                                  pbuf_pool = p;                        \
                                  DEC_PBUF_STATS;                       \
                                } while (0)

PBUF_POOL_FREE

#define PBUF_POOL_FREE

(

p

)

Value:

do {                                         \
                             LWP_SemWait(pbuf_pool_free_sem);          \
                             PBUF_POOL_FAST_FREE(p);                    \
                             LWP_SemPost(pbuf_pool_free_sem);        \
                           } while (0)

Function Documentation

pbuf_alloc()

struct pbuf* pbuf_alloc	(	pbuf_layer	l,
		u16_t	length,
		pbuf_flag	flag
	)

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

flag	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.

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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()

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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.

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pbuf_clen()

u8_t pbuf_clen

(

struct pbuf *

p

)

Count number of pbufs in a chain

Parameters

p	first pbuf of chain

Returns

the number of pbufs in a chain

pbuf_dechain()

struct pbuf* pbuf_dechain

(

struct pbuf *

p

)

Dechains the first pbuf from its succeeding pbufs in the chain.

Makes p->tot_len field equal to p->len.

Parameters

p	pbuf to dechain

Returns

remainder of the pbuf chain, or NULL if it was de-allocated.

Note

May not be called on a packet queue.

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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

pbuf	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).

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pbuf_header()

u8_t pbuf_header	(	struct pbuf *	p,
		s16_t	header_size_increment
	)

Adjusts the payload pointer to hide or reveal headers in the payload.

Adjusts the ->payload pointer so that space for a header (dis)appears in the pbuf payload.

The ->payload, ->tot_len and ->len fields are adjusted.

Parameters

hdr_size_inc

Number of bytes to increment header size which increases the size of the pbuf. New space is on the front. (Using a negative value decreases the header size.) If hdr_size_inc is 0, this function does nothing and returns succesful.

PBUF_ROM and PBUF_REF type buffers cannot have their sizes increased, so the call will fail. A check is made that the increase in header size does not move the payload pointer in front of the start of the buffer.

Returns

non-zero on failure, zero on success.

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pbuf_init()

void pbuf_init

(

void

)

Initializes the pbuf module.

A large part of memory is allocated for holding the pool of pbufs. The size of the individual pbufs in the pool is given by the size parameter, and the number of pbufs in the pool by the num parameter.

After the memory has been allocated, the pbufs are set up. The ->next pointer in each pbuf is set up to point to the next pbuf in the pool.

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pbuf_pool_alloc()

static struct pbuf* pbuf_pool_alloc ( void  )

static

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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.

Bug:

Cannot grow the size of a pbuf (chain) (yet).

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pbuf_ref()

void pbuf_ref

(

struct pbuf *

p

)

Increment the reference count of the pbuf.

Parameters

p	pbuf to increase reference counter of

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pbuf_take()

struct pbuf* pbuf_take

(

struct pbuf *

p

)

Create PBUF_POOL (or PBUF_RAM) copies of PBUF_REF pbufs.

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

Go through a pbuf chain and replace any PBUF_REF buffers with PBUF_POOL (or PBUF_RAM) pbufs, each taking a copy of the referenced data.

Note

You MUST explicitly use p = pbuf_take(p); The pbuf you give as argument, may have been replaced by a (differently located) copy through pbuf_take()!

Any replaced pbufs will be freed through pbuf_free(). This may deallocate them if they become no longer referenced.

Parameters

p	Head of pbuf chain to process

Returns

Pointer to head of pbuf chain

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Variable Documentation

pbuf_pool

struct pbuf* pbuf_pool = NULL

static

pbuf_pool_alloc_lock

volatile u8_t pbuf_pool_alloc_lock

static

pbuf_pool_free_lock

volatile u8_t pbuf_pool_free_lock

static

pbuf_pool_free_sem

sys_sem pbuf_pool_free_sem

static

pbuf_pool_memory

u8_t pbuf_pool_memory[MEM_ALIGNMENT - 1+PBUF_POOL_SIZE *MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE+sizeof(struct pbuf))]

static