今天开始学习ucore的lab。
按照lab0的文档，显示介绍了80386的4个工作模式：real-address
mode, protected mode, SMM mode, virtual 8086 mode.
ia-32-architectures-software-developer-system-programming-manual-VOL3_Feb2014中的Figure
2-3. Transitions Among the Processor’s Operating Modes是4个mode FSM。
在Lab
0的2.6节介绍了ucore的编程方法：用C实现C++的OOP思想：interface(API)。在Absolute C++的Chap
6的tip里面讲了：princeple of encapsulation is on: separate "interface" and
"implementation of class".
在http://www.tutorialspoint.com/cplusplus/cpp_interfaces.htm
里面讲了interface一般是用abstract class作为base class。
在 http://www.bottomupcs.com/abstration.html
详述了linux kernal, system with large C based code. 通过使用function
pointer来模拟C++的interface/class的OOP。
在 understanding and
using pointer in C 中的function pointer里面提到一个drawback: "One concern
regarding the use of function pointers is a potentially slower
running program. The processor may not be able to use branch prediction in
conjunction with pipelining."
这印证了ucore lab0的说法：“Core
的面向对象编程方法，目前主要是采用了类似
C++的接口（interface）概念，即是让实现 细节不同的某类内核子系统（比如物理内存分配器、调度器，文件系统等）有共同的操作方式
... 接口在 C 语言中，表现为一组函数指针的集合。放在 C++ 中，即为虚表。”
先复习一下 function pointer,
structure in C.
1 /*
2 * function pointers in C as the interface in C++
3 * used widely in linux kernal, or lab0 of ucore
4 * Jun 8, 2014
5 *
6 * http://www.bottomupcs.com/abstration.html#ftn.d5e116
7 */
8
9 #include <stdio.h>
10
11 /* The API to implement */
12 struct greet_api {
13 int (*say_hello)(char *name);
14 int (*say_goodbye)(void);
15 };
16
17 /* Our implementation of the hello function */
18 int say_hello_fn(char *name) {
19 printf("Hello %s\n", name);
20 return 0;
21 }
22
23 /* Our implementation of the goodbye function */
24 int say_goodbye_fn(void) {
25 printf("Goodbye\n");
26 return 0;
27 }
28
29 /* A struct implementing the API */
30 /*
31 * Designated Initializers for Structures
32 * See <C primer plus 5th>
33 * the name of a function can be used to represent the address of the function
34 */
35 struct greet_api greet_api = { .say_hello = say_hello_fn, .say_goodbye =
36 say_goodbye_fn };
37
38 /* main() doesn‘t need to know anything about how the
39 * say_hello/goodbye works, it just knows that it does */
40 int main(int argc, char *argv[]) {
41 greet_api.say_hello(argv[1]);
42 greet_api.say_goodbye();
43
44 printf("%p, %p, %p\n", greet_api.say_hello, say_hello_fn, &say_hello_fn);
45
46 //exit(0);
47 return 0;
48 }
然后可以看看ucore是怎么用structure of function pointer去实现一个C++的interface。
在lab2/kern/mm/pmm.h里面的pmm_manager:
1 // pmm_manager is a physical memory management class. A special pmm manager - XXX_pmm_manager
2 // only needs to implement the methods in pmm_manager class, then XXX_pmm_manager can be used
3 // by ucore to manage the total physical memory space.
4 struct pmm_manager {
5 const char *name; // XXX_pmm_manager‘s name
6 void (*init)(void); // initialize internal description&management data structure
7 // (free block list, number of free block) of XXX_pmm_manager
8 void (*init_memmap)(struct Page *base, size_t n); // setup description&management data structcure according to
9 // the initial free physical memory space
10 struct Page *(*alloc_pages)(size_t n); // allocate >=n pages, depend on the allocation algorithm
11 void (*free_pages)(struct Page *base, size_t n); // free >=n pages with "base" addr of Page descriptor structures(memlayout.h)
12 size_t (*nr_free_pages)(void); // return the number of free pages
13 void (*check)(void); // check the correctness of XXX_pmm_manager
14 };
15
16 extern const struct pmm_manager *pmm_manager;
然后在2.6.2.1
双向循环链表中学习了ucore中常用的数据结构。这在uc/os-II和freertos里面的freelistTable也用到了。
注意：ucore的double linked list 和C/C++里面的设计方法有点点区别。这是为了适应不同功能的双向链表：有保存task
table的，有空闲内存块列表，或者、内存页链表等等。
ucore lab0的学习: 2.6 了解 ucore 编程方法