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 }

 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;