链表 mmalloc

/************************

 * 链表定义

************************/

typedef struct blockhead_t {

Int32 signature;

Bool allocated;

unsigned long size;

struct blockhead_t *next;

struct blockhead_t *prev;

} blockhead;

/**********************

 * 链表头

**********************/

static blockhead *gHeapBase = NULL; //初始化为heap起始地址，大小为系统heap设置的大小,未标记,next,prev均为NULL

/*************************************

 * 为用户分配size大小的heap

 *size - 需要分配的大小

 *return: 成功时分配的地址

  失败时NULL

*************************************/

void *mmalloc(unsigned long size) 

{

blockhead *blockptr = gHeapBase;

blockhead *newblock;

Bool compacted = FALSE;

size = (size+7)&~7; /* unsigned long align the size */ //没看明白什么意思??????????????????????????

DPRINTK("malloc(): size = 0x%08lx\n", size);

while (blockptr != NULL) 

{

if (blockptr->allocated == FALSE) //当前块未标记，可以使用

{

if (blockptr->size >= size) 

{

blockptr->allocated=TRUE;

if ((blockptr->size - size) > sizeof(blockhead)) //当前块满足要求，分配成功，设置heap链表

{

newblock = (blockhead *)((unsigned char *)(blockptr) + sizeof(blockhead) + size);

newblock->signature = BLOCKHEAD_SIGNATURE;

newblock->prev = blockptr;

newblock->next = blockptr->next;

newblock->size = blockptr->size - size - sizeof(blockhead);

newblock->allocated = FALSE;

blockptr->next = newblock;

blockptr->size = size;

} 

else //blockptr->size - size < sizeof(blockhead)

{ //当前块size过小，无法分配所需空间

break; //为什么不继续看下一块而直接退出呢??????????????????????????

}

} 

else //blockptr->size < size,当前块小于所需分配大小

{

if ((blockptr->next == NULL) && (compacted == FALSE)) //这个if毫无意义?

{ //若存在已经丢弃的heap而用户未主动释放,程序自行释放?

if (compact_heap())

{ //compact_heap函数应该是完成整合可合并的几个heap为一整体

compacted=TRUE;

blockptr = gHeapBase;

continue;

}

}

}

}

blockptr = blockptr->next; //当前block无法满足要求，看下一块

}//end for while

DPRINTK("malloc(): returning blockptr = 0x%08lx\n", blockptr);

if (blockptr == NULL) //分配失败

printk("Error: malloc(), out of storage. size = 0x%x\n", size);

return (blockptr != NULL) ? ((unsigned char *)(blockptr)+sizeof(blockhead)) : NULL; //返回指向分配地址的指针

}

static int compact_heap(void) 

{

// return non-zero if heap was compacted

return 0;

}