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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 1 | pmbaty | 1 | // doslabel.c -- read/set the volume labels of DOS partitions by Pierre-Marie Baty <pm@pmbaty.com> |
| 2 | |||
| 3 | #include <stdio.h> |
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| 4 | #include <stdlib.h> |
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| 5 | #include <string.h> |
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| 6 | #include <errno.h> |
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| 7 | #include <ctype.h> |
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| 8 | |||
| 9 | |||
| 10 | int main (int argc, char **argv) |
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| 11 | { |
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| 12 | // program entrypoint |
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| 13 | |||
| 14 | typedef struct __attribute__((packed)) fatfs_header_s |
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| 15 | { |
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| 16 | unsigned char bootstrap_code[3]; // offset 0 |
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| 17 | char oem_name_and_version[8]; // offset 3 |
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| 18 | unsigned short bytes_per_sector; // offset 11 |
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| 19 | unsigned char sectors_per_cluster; // offset 13 |
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| 20 | unsigned short reserved_sectors; // offset 14 |
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| 21 | unsigned char fat_copies; // offset 16 |
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| 22 | unsigned short rootdir_entries; // offset 17 |
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| 23 | unsigned short total_sectors; // offset 19 |
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| 24 | unsigned char media_type; // offset 21 |
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| 25 | unsigned short sectors_per_fat; // offset 22 |
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| 26 | unsigned short sectors_per_track; // offset 24 |
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| 27 | unsigned short heads; // offset 26 |
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| 28 | unsigned short hidden_sectors; // offset 28; |
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| 29 | } fatfs_header_t; |
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| 30 | |||
| 31 | unsigned char first_sector[512]; |
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| 32 | fatfs_header_t *fat_header; |
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| 33 | const char *dev_pathname; |
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| 34 | size_t label_offset; |
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| 35 | size_t char_index; |
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| 36 | char *new_label; |
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| 37 | char label[12]; |
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| 38 | FILE *fp; |
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| 39 | |||
| 40 | // consistency checks |
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| 41 | if ((argc < 2) || (*(argv[1]) == '-')) |
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| 42 | { |
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| 43 | fprintf (stderr, "usage: doslabel <device> [new-label]\n"); |
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| 44 | exit (1); |
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| 45 | } |
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| 46 | |||
| 47 | dev_pathname = argv[1]; // read arguments |
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| 48 | new_label = (argc > 2 ? argv[2] : NULL); |
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| 49 | |||
| 50 | // open and read the first sector of the passed device pathname |
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| 51 | if (((fp = fopen (dev_pathname, "r+b")) == NULL) || (fread (first_sector, 512, 1, fp) != 1)) |
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| 52 | { |
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| 53 | fprintf (stderr, "error: can't read first sector of %s: %s\n", dev_pathname, strerror (errno)); |
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| 54 | exit (1); |
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| 55 | } |
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| 56 | |||
| 57 | // consistency checks |
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| 58 | fat_header = (fatfs_header_t *) first_sector; |
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| 59 | |||
| 60 | // is it a FAT12/FAT16 or FAT32 BPB ? |
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| 61 | if ((memcmp (&first_sector[510], "\x55\xaa", 2) == 0) |
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| 62 | && ( (fat_header->bytes_per_sector == 512) |
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| 63 | || (fat_header->bytes_per_sector == 1024) |
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| 64 | || (fat_header->bytes_per_sector == 2048) |
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| 65 | || (fat_header->bytes_per_sector == 4096)) |
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| 66 | && ( (fat_header->sectors_per_cluster == 1) |
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| 67 | || (fat_header->sectors_per_cluster == 2) |
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| 68 | || (fat_header->sectors_per_cluster == 4) |
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| 69 | || (fat_header->sectors_per_cluster == 8) |
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| 70 | || (fat_header->sectors_per_cluster == 16) |
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| 71 | || (fat_header->sectors_per_cluster == 32) |
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| 72 | || (fat_header->sectors_per_cluster == 64) |
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| 73 | || (fat_header->sectors_per_cluster == 128)) |
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| 74 | && ( (fat_header->reserved_sectors == 1) |
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| 75 | || (fat_header->reserved_sectors == 32))) |
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| 76 | label_offset = (fat_header->sectors_per_fat != 0 ? 43 : 71); |
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| 77 | else |
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| 78 | { |
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| 79 | // volume labels in exFAT filesystems are actually directory entries with a special flag |
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| 80 | // we don't support that at the moment (FIXME) |
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| 81 | // that's fine, because EFI partitions can't be exFAT -- only FAT12/16. |
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| 82 | fprintf (stderr, "error: only FAT12/FAT16/FAT32 filesystems are supported\n"); |
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| 83 | exit (1); |
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| 84 | } |
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| 85 | |||
| 86 | // do we want to read or set the volume label ? |
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| 87 | if (new_label == NULL) |
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| 88 | { |
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| 89 | // read the label and strip it from trailing spaces |
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| 90 | memcpy (label, &first_sector[label_offset], 11); |
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| 91 | label[11] = 0; |
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| 92 | for (char_index = 10; char_index > 0; char_index--) |
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| 93 | if (label[char_index] == ' ') |
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| 94 | label[char_index] = 0; |
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| 95 | else |
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| 96 | break; |
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| 97 | if (label[char_index] == ' ') |
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| 98 | label[char_index] = 0; |
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| 99 | |||
| 100 | // print it to the standard output |
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| 101 | printf ("%s\n", label); |
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| 102 | } |
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| 103 | else if (argc == 3) |
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| 104 | { |
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| 105 | // write a new DOS partition label |
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| 106 | fseek (fp, label_offset, SEEK_SET); // can't fail |
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| 107 | memset (label, ' ', sizeof (label)); |
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| 108 | memcpy (label, new_label, strlen (new_label)); |
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| 109 | if (fwrite (label, 11, 1, fp) != 1) |
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| 110 | { |
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| 111 | fprintf (stderr, "error: can't write new volume label to %s: %s\n", dev_pathname, strerror (errno)); |
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| 112 | exit (1); |
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| 113 | } |
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| 114 | } |
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| 115 | |||
| 116 | fclose (fp); |
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| 117 | exit (0); |
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| 118 | } |