  1#include <stdio.h>
  2#include <stdlib.h>
  3#include <string.h>
  4#include <assert.h>
  5#include <fcntl.h>
  6#include <unistd.h>
  7#include <sys/mman.h>
  8#include "fat32.h"
  9
 10struct fat32hdr *hdr;
 11
 12void *map_disk(const char *fname);
 13void dfs(u32 clusId, int depth, int is_dir);
 14
 15int main(int argc, char *argv[]) {
 16  if (argc < 2) {
 17    fprintf(stderr, "Usage: %s fs-image\n", argv[0]);
 18    exit(1);
 19  }
 20
 21  setbuf(stdout, NULL);
 22
 23  assert(sizeof(struct fat32hdr) == 512); // defensive
 24  assert(sizeof(struct fat32dent) == 32); // defensive
 25
 26  // map disk image to memory
 27  hdr = map_disk(argv[1]);
 28
 29  // file system traversal
 30  dfs(hdr->BPB_RootClus, 0, 1);
 31
 32  munmap(hdr, hdr->BPB_TotSec32 * hdr->BPB_BytsPerSec);
 33}
 34
 35void *map_disk(const char *fname) {
 36  int fd = open(fname, O_RDWR);
 37
 38  if (fd < 0) {
 39    goto release;
 40  }
 41
 42  off_t size = lseek(fd, 0, SEEK_END);
 43  if (size == -1) {
 44    goto release;
 45  }
 46
 47  struct fat32hdr *hdr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 48  if (hdr == (void *)-1) {
 49    goto release;
 50  }
 51
 52  close(fd);
 53
 54  assert(hdr->Signature_word == 0xaa55); // this is an MBR
 55  assert(hdr->BPB_TotSec32 * hdr->BPB_BytsPerSec == size);
 56
 57  printf("%s: DOS/MBR boot sector, ", fname);
 58  printf("OEM-ID \"%s\", ", hdr->BS_OEMName);
 59  printf("sectors/cluster %d, ", hdr->BPB_SecPerClus);
 60  printf("sectors %d, ", hdr->BPB_TotSec32);
 61  printf("sectors %d, ", hdr->BPB_TotSec32);
 62  printf("sectors/FAT %d, ", hdr->BPB_FATSz32);
 63  printf("serial number 0x%x\n", hdr->BS_VolID);
 64  return hdr;
 65
 66release:
 67  perror("map disk");
 68  if (fd > 0) {
 69    close(fd);
 70  }
 71  exit(1);
 72}
 73
 74u32 next_cluster(int n) {
 75  // RTFM: Sec 4.1
 76  u32 *fat = (u32 *)((u8 *)hdr + hdr->BPB_RsvdSecCnt * hdr->BPB_BytsPerSec);
 77  return fat[n];
 78}
 79
 80void *cluster_to_sec(int n) {
 81  // RTFM: Sec 3.5 and 4 (TRICKY)
 82  // Don't copy code. Write your own.
 83  u32 DataSec = hdr->BPB_RsvdSecCnt + hdr->BPB_NumFATs * hdr->BPB_FATSz32;
 84  DataSec += (n - 2) * hdr->BPB_SecPerClus;
 85  return ((char *)hdr) + DataSec * hdr->BPB_BytsPerSec;
 86}
 87
 88void get_filename(struct fat32dent *dent, char *buf) {
 89  // RTFM: Sec 6.1
 90  int len = 0;
 91  for (int i = 0; i < sizeof(dent->DIR_Name); i++) {
 92    if (dent->DIR_Name[i] != ' ') {
 93      if (i == 8) buf[len++] = '.';
 94      buf[len++] = dent->DIR_Name[i];
 95    }
 96  }
 97  buf[len] = '\0';
 98}
 99
100void dfs(u32 clusId, int depth, int is_dir) {
101  // RTFM: Sec 6
102  for (; clusId < CLUS_INVALID; clusId = next_cluster(clusId)) {
103    if (is_dir) {
104      int ndents = hdr->BPB_BytsPerSec * hdr->BPB_SecPerClus / sizeof(struct fat32dent);
105
106      for (int d = 0; d < ndents; d++) {
107        struct fat32dent *dent = (struct fat32dent *)cluster_to_sec(clusId) + d;
108        if (dent->DIR_Name[0] == 0x00 ||
109            dent->DIR_Name[0] == 0xe5 ||
110            dent->DIR_Attr & ATTR_HIDDEN) continue;
111
112        char fname[32];
113        get_filename(dent, fname);
114
115        for (int i = 0; i < 4 * depth; i++) putchar(' ');
116        printf("[%-12s] %6.1lf KiB    ", fname, dent->DIR_FileSize / 1024.0);
117
118        u32 dataClus = dent->DIR_FstClusLO | (dent->DIR_FstClusHI << 16);
119        if (dent->DIR_Attr & ATTR_DIRECTORY) {
120          printf("\n");
121          if (dent->DIR_Name[0] != '.') {
122            dfs(dataClus, depth + 1, 1);
123          }
124        } else {
125          dfs(dataClus, depth + 1, 0);
126          printf("\n");
127        }
128      }
129    } else {
130      printf("#%d ", clusId);
131    }
132  }
133}
28. FAT 和 UNIX 文件系统¶

Take-away Messages¶

课后习题/编程作业¶

1. 阅读材料¶
