1 typedef struct ListStructTag
2 {
3 int signature; /* debugging aid */
4 int percentIncrease; /* %of current size to increase by when list is out of space */
5 int minNumItemsIncrease; /* fixed number of items to increase by when list is out of space */
6 int listSize; /* number of items than can fit in the currently allocated memory */
7 int itemSize; /* the size of each item in the list (same for every item) */
8 int numItems; /* number of items currently in the list */
9 unsigned char itemList[1]; /* resizable array of list elements */
10 } ListStruct;
11 typedef struct ListStructTag **list_t; /* The list abstract data type */
list_t devlist = 0; 即ListStructTag ** devlist;
devlist是个全局变量，devlist 中的值是ListStruct结构的指针的指针。即有
list_t devlist (ListStruct *) ListStruct
+----------+ +-----------+ +-------------+
| | ------> | | ------> | …… |
+----------+ +-----------+ + +
| …… |
+ +
| …… |
+-------------+
39 typedef void **Handle;
40 Handle NewHandle (unsigned int numBytes)
41 {
42 void *memPtr;
43 HandleRecord *hanPtr;
44 memPtr = calloc (numBytes, 1);
45 hanPtr = (HandleRecord *) calloc (sizeof (HandleRecord), 1);
46 if (hanPtr && (memPtr || numBytes == 0)) {
47 hanPtr->ptr = memPtr;
48 hanPtr->size = numBytes;
49 return (Handle) hanPtr;
50 } else {
51 free (memPtr);
52 free (hanPtr);
53 return NULL;
54 }
55 }
函数传进来的numBytes为sizeof (ListStruct)， 即一个ListStruct结构大小的空间
44行，申请ListStruct结构大小的空间
45行，申请HandleRecord结构大小的空间，HandleRecord结构有两个成员
typedef struct
{
void *ptr;
unsigned int size;
} HandleRecord;
46行，hanPtr和memPtr申请成功时，if判断为真，则执行47 48行，最后返回void **hanPtr
void **hanPtr HandleRecord ListStruct
+-----------+ +-----------+ +-------------+
| | -----> | void *ptr | ------> | …… |
+-----------+ +-----------+ + +
| size | | …… |
+-----------+ + +
| …… |
+-------------+
23 list_t ListCreate (int elementSize)
24 {
25 list_t list;
26 list = (list_t) (NewHandle (sizeof (ListStruct))); /* create empty list */
27 if (list) {
28 (*list)->signature = LIST_SIGNATURE;
29 (*list)->numItems = 0;
30 (*list)->listSize = 0;
31 (*list)->itemSize = elementSize;
32 (*list)->percentIncrease =
33 kDefaultAllocationPercentIncrease; //10
34 (*list)->minNumItemsIncrease =
35 kDefaultAllocationminNumItemsIncrease; //4
36 }
37 return list;
38 }
23行，传进来的参数为sizeof (device_t)
26行，调用NewHandle(),并将返回值格式化成list_t类型
28～35行，初始化 ListStruct 结构
HandleRecord ListStruct
+-----------+ +-----------------+ +-----------------------------+
| | -----> | ListStruct *ptr | ------> | signature = LIST_SIGNATURE |
+-----------+ +-----------------+ +-----------------------------+
void **hanPtr | size | | percentIncrease = 10 |
| +-----------------+ +-----------------------------+
v return from NewHandle() | minNumItemsIncrease =4 |
list_t list +-----------------------------+
| listSize = 0 |
+-----------------------------+
| itemSize = sizeof(device_t) |
+-----------------------------+
|numItems = 0 |
+-----------------------------+
| unsigned char itemList[1] |
+-----------------------------+
12 int devices_init (void)
13 {
14 /* Initialize the list */
15 devlist = ListCreate (sizeof (device_t));
16 if (devlist == NULL) {
17 eputs ("Cannot initialize the list of devices!\n");
18 return -1;
19 }
20 drv_system_init ();
21 return (0);
22 }
15行，ListCreate返回给devlist， 所以现在的数据结构如下
HandleRecord ListStruct
+-----------+ +-----------------+ +-----------------------------+
| | -----> | ListStruct *ptr | ------> | signature = LIST_SIGNATURE |
+-----------+ +-----------------+ +-----------------------------+
void **hanPtr | size | | percentIncrease = 10 |
| +-----------------+ +-----------------------------+
v return from NewHandle() | minNumItemsIncrease =4 |
list_t list +-----------------------------+
| | listSize = 0 |
v return from ListCreate() +-----------------------------+
list_t devlist | itemSize = sizeof(device_t) |
+-----------------------------+
| numItems = 0 |
+-----------------------------+
| unsigned char itemList[1] |
+-----------------------------+
20行， 初始系统设备
56 typedef struct {
57 int flags; /* Device flags: input/output/system */
58 int ext; /* Supported extensions */
59 char name[16]; /* Device name */
60 int (*start) (void); /* To start the device */
61 int (*stop) (void); /* To stop the device */
62 void (*putc) (const char c); /* To put a char */
63 void (*puts) (const char *s); /* To put a string (accelerator) */
64 int (*tstc) (void); /* To test if a char is ready... */
65 int (*getc) (void); /* To get that char */
66 void *priv; /* Private extensions */
67 } device_t;
68 static void drv_system_init (void)
69 {
70 device_t dev;
71 memset (&dev, 0, sizeof (dev));
72 strcpy (dev.name, "serial");
73 dev.flags = DEV_FLAGS_OUTPUT | DEV_FLAGS_INPUT | DEV_FLAGS_SYSTEM;
74 dev.putc = serial_putc;
75 dev.puts = serial_puts;
76 dev.getc = serial_getc;
77 dev.tstc = serial_tstc;
78 device_register (&dev);
79 }
73～77 初始串口设备，一般我们也是使用串口来打印目标板信息以及向目标板发送命令。对应56~67行，可以
清楚这些成员的意义。
78行，注册这个设备。"serial"这个设备继续跟踪下去
80 #define LIST_START -1 /* Handy Constants that substitute for item positions */
81 #define LIST_END 0 /* END_OF_LIST means one past current length of list when */
82 int device_register (device_t * dev)
83 {
84 ListInsertItem (devlist, dev, LIST_END);
85 return 0;
86 }
87 int ListInsertItem (list_t list, void *ptrToItem, int itemPosition)
88 {
89 return ListInsertItems (list, ptrToItem, itemPosition, 1);
90 }
87行，进入的参数分别为1 devlist, 这个是全局变量
2 dev 即drv_system_init中初始的"serial"设备 device_t dev 的指针
3 LIST_END == 0
91 int ListInsertItems (list_t list, void *ptrToItems, int firstItemPosition,
92 int numItemsToInsert)
93 {
94 int numItems = (*list)->numItems;
95 if (firstItemPosition == numItems + 1)
96 firstItemPosition = LIST_END;
97 else if (firstItemPosition > numItems)
98 return 0;
99 if ((*list)->numItems >= (*list)->listSize) {
100 if (!ExpandListSpace (list, -numItemsToInsert))
101 return 0;
102 }
103 if (firstItemPosition == LIST_START) {
104 if (numItems == 0) {
105 /* special case for empty list */
106 firstItemPosition = LIST_END;
107 } else {
108 firstItemPosition = 1;
109 }
110 }
111 if (firstItemPosition == LIST_END) { /* add at the end of the list */
112 if (ptrToItems)
113 memcpy (ITEMPTR (list, numItems), ptrToItems,
114 (*list)->itemSize * numItemsToInsert);
115 else
116 memset (ITEMPTR (list, numItems), 0,
117 (*list)->itemSize * numItemsToInsert);
118 (*list)->numItems += numItemsToInsert;
119 } else { /* move part of list up to make room for new item */
120 memmove (ITEMPTR (list, firstItemPosition - 1 + numItemsToInsert),
121 ITEMPTR (list, firstItemPosition - 1),
122 (numItems + 1 - firstItemPosition) * (*list)->itemSize);
123 if (ptrToItems)
124 memmove (ITEMPTR (list, firstItemPosition - 1), ptrToItems,
125 (*list)->itemSize * numItemsToInsert);
126 else
127 memset (ITEMPTR (list, firstItemPosition - 1), 0,
128 (*list)->itemSize * numItemsToInsert);
129 (*list)->numItems += numItemsToInsert;
130 }
131 return 1;
132 }
94行，目前设备列表list里的设备数 ，这里注册第一个设备"serial"，为0
95～97 此时firstItemPosition == LIST_END == 0, 所以这里判断均为假，跳过
100 行中 ExpandListSpace()会增加list里的设备数，并为这个设备分配相应的空间，这个空间是用relloc
这种机制来分配的，保证了这里的device_t与前面的ListStructTag连在一起
113行 将drv_system_init里初始的device_t结构内容复制到新分配的空间里
118行 设备数加1
完成了设备的注册
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