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R0.14 patch 1

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November 10, 2019

Old floppy disks formatted with MS-DOS 2.x and 3.x cannot be mounted.

This is because the boot sector lacks "FAT" string and 0xAA55 signature.
This commit is contained in:
Christopher Williams
2019-11-14 17:38:11 -07:00
parent 258d0cbbf0
commit cf1fa00811
1 changed files with 24 additions and 10 deletions
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source/ff.c
+24 -10
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@@ -3290,23 +3290,37 @@ static DWORD make_rand (
/* Check what the sector is */
static UINT check_fs ( /* 0:FAT VBR, 1:exFAT VBR, 2:Valid BS but not FAT, 3:Invalid BS, 4:Disk error */
static UINT check_fs ( /* 0:FAT VBR, 1:exFAT VBR, 2:Not FAT and valid BS, 3:Not FAT and invalid BS, 4:Disk error */
FATFS* fs, /* Filesystem object */
LBA_t sect /* Sector to load and check if it is an FAT-VBR or not */
)
{
WORD w, sign;
BYTE b;
fs->wflag = 0; fs->winsect = (LBA_t)0 - 1; /* Invaidate window */
if (move_window(fs, sect) != FR_OK) return 4; /* Load the boot sector */
if (ld_word(fs->win + BS_55AA) != 0xAA55) return 3; /* Check boot signature (always here regardless of the sector size) */
if (FF_FS_EXFAT && !mem_cmp(fs->win + BS_JmpBoot, "\xEB\x76\x90" "EXFAT ", 11)) return 1; /* Check if exFAT VBR */
if (fs->win[BS_JmpBoot] == 0xE9 || fs->win[BS_JmpBoot] == 0xEB || fs->win[BS_JmpBoot] == 0xE8) { /* Valid JumpBoot code? */
if (!mem_cmp(fs->win + BS_FilSysType, "FAT", 3)) return 0; /* Is it an FAT VBR? */
if (!mem_cmp(fs->win + BS_FilSysType32, "FAT32", 5)) return 0; /* Is it an FAT32 VBR? */
sign = ld_word(fs->win + BS_55AA);
#if FF_FS_EXFAT
if (sign == 0xAA55 && !mem_cmp(fs->win + BS_JmpBoot, "\xEB\x76\x90" "EXFAT ", 11)) return 1; /* It is an exFAT VBR */
#endif
b = fs->win[BS_JmpBoot];
if (b == 0xEB || b == 0xE9 || b == 0xE8) { /* Valid JumpBoot code? (short jump, near jump or near call) */
if (sign == 0xAA55 && !mem_cmp(fs->win + BS_FilSysType32, "FAT32 ", 8)) return 0; /* It is an FAT32 VBR */
/* FAT volumes formatted with early MS-DOS lack boot signature and FAT string, so that we need to identify the FAT VBR without them. */
w = ld_word(fs->win + BPB_BytsPerSec);
if ((w & (w - 1)) == 0 && w >= FF_MIN_SS && w <= FF_MAX_SS) { /* Properness of sector size */
b = fs->win[BPB_SecPerClus];
if (b != 0 && (b & (b - 1)) == 0 /* Properness of cluster size */
&& (fs->win[BPB_NumFATs] == 1 || fs->win[BPB_NumFATs] == 2) /* Properness of number of FATs */
&& ld_word(fs->win + BPB_RootEntCnt) != 0 /* Properness of root entry count */
&& ld_word(fs->win + BPB_FATSz16) != 0) { /* Properness of FAT size */
return 0; /* Sector can be presumed an FAT VBR */
}
}
}
return 2; /* Valid BS but not FAT */
return sign == 0xAA55 ? 2 : 3; /* Not an FAT VBR (valid or invalid BS) */
}