When a file is mmap'd into memory, when is its contents loaded from disk? How can you verify this using 3000test?

/* 3000test.c */ 

 2 

 3 

 4 

 5 

 6 

 7 #include  

 8 #include  

 9 #include  

10 #include  

11 #include  

12 #include  

13 #include  

14 #include  

15 #include  

16 

17 void report_error(char *error) 

18 { 

19 fprintf(stderr, "Error: %s ", error); 

20 

21 exit(-1); 

22 } 

23 

24 int main(int argc, char *argv[]) 

25 { 

26 struct stat statbuf; 

27 char *fn; 

28 int fd; 

29 size_t len, i, count; 

30 

31 char *data; 

32 

33 if (argc < 2) { 

34 if (argc < 1) { 

35 report_error("no command line"); 

36 fprintf(stderr, "Usage: %s  ", argv[0]); 

37 } else { 

38 report_error("Not enough arguments"); 

39 fprintf(stderr, "Usage: %s  ", argv[0]); 

40 } 

41 } 

42 

43 fn = argv[1]; 

44 

45 if (stat(fn, &statbuf)) { 

46 report_error(strerror(errno)); 

47 } 

48 

49 len = statbuf.st_size; 

50 printf("File %s:  ", fn); 

51 printf(" inode %ld ", statbuf.st_ino); 

52 printf(" length %ld ", len); 

53 

54 if (S_ISREG(statbuf.st_mode)) { 

55 fd = open(fn, O_RDONLY); 

56 if (fd == -1) { 

57 report_error(strerror(errno)); 

58 } 

59 data = (char *) mmap(NULL, len, 

60 PROT_READ, MAP_SHARED, fd, 0); 

61 if (data == MAP_FAILED) { 

62 report_error(strerror(errno)); 

63 } 

64 

65 count = 0; 

66 for (i=0; i 
67 if (data[i] == 'a') { 
 
68 count++; 
 
69 } 
 
70 } 
 
71 
 
72 printf(" a count %ld ", count); 
 
73 
 
74 if (munmap(data, len) == -1) { 
 
75 report_error(strerror(errno)); 
 
76 } 
 
77 close(fd); 
 
78 } 
 
79 
 
80 return 0; 
 
81 }