packet.h

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

typedef struct Packet Packet;
typedef struct Mem Mem;
typedef struct Frag Frag;

enum {
	BigMemSize = MaxFragSize,
	SmallMemSize = BigMemSize/8,
	NLocalFrag = 2,
};

/* position to carve out of a Mem */
enum {
	PFront,
	PMiddle,
	PEnd,
};

struct Mem
{
	Lock lk;
	int ref;
	uchar *bp;
	uchar *ep;
	uchar *rp;
	uchar *wp;
	Mem *next;
};

enum {
	FragLocalFree,
	FragLocalAlloc,
	FragGlobal,
};
	
struct Frag
{
	int state;
	Mem *mem;
	uchar *rp;
	uchar *wp;
	Frag *next;
};

struct Packet
{
	int size;
	int asize;  /* allocated memmory - always greater than size */
	
	Packet *next;
	
	Frag *first;
	Frag *last;
	
	Frag local[NLocalFrag];
};