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Add classes for mounting FAT16/32 without help from OS

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Minimal implementation for reading/writing files in the root
directory of a FAT16/FAT32 file system.

Can read/write from raw disk devices, and no longer relies on
operating system support for mounting the file system.

Currently assumes Imager will always be run on 'little endian'
architectures such as Intel and ARM (at least under Linux).
If there is a use-case for big-endian (anybody still using Sparc?)
this may be revisited later.
This commit is contained in:
Floris Bos 2022-11-14 20:18:36 +01:00
parent 30225187bd
commit 142ddfc037
10 changed files with 1193 additions and 1 deletions
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145
src/devicewrapperstructs.h Normal file
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#ifndef DEVICEWRAPPERSTRUCTS_H
#define DEVICEWRAPPERSTRUCTS_H
/*
* SPDX-License-Identifier: Apache-2.0
* Copyright (C) 2022 Raspberry Pi Ltd
*/
/* MBR on-disk structures */
struct mbr_partition_entry {
unsigned char bootable;
char begin_hsc[3];
unsigned char id;
char end_hsc[3];
unsigned int starting_sector;
unsigned int nr_of_sectors;
} __attribute__ ((packed));
struct mbr_table {
char bootcode[440];
unsigned char diskid[4];
unsigned char flags[2];
mbr_partition_entry part[4];
unsigned char signature[2];
} __attribute__ ((packed));
/* File Allocation Table
* https://academy.cba.mit.edu/classes/networking_communications/SD/FAT.pdf
*/
struct fat16_bpb {
uint8_t BS_jmpBoot[3];
char BS_OEMName[8];
uint16_t BPB_BytsPerSec;
uint8_t BPB_SecPerClus;
uint16_t BPB_RsvdSecCnt;
uint8_t BPB_NumFATs;
uint16_t BPB_RootEntCnt;
uint16_t BPB_TotSec16;
uint8_t BPB_Media;
uint16_t BPB_FATSz16;
uint16_t BPB_SecPerTrk;
uint16_t BPB_NumHeads;
uint32_t BPB_HiddSec;
uint32_t BPB_TotSec32;
uint8_t BS_DrvNum;
uint8_t BS_Reserved1;
uint8_t BS_BootSig;
uint32_t BS_VolID;
char BS_VolLab[11];
char BS_FilSysType[8];
uint8_t Zeroes[448];
uint8_t Signature[2]; /* 0x55aa */
} __attribute__ ((packed));
struct fat32_bpb {
uint8_t BS_jmpBoot[3];
char BS_OEMName[8];
uint16_t BPB_BytsPerSec;
uint8_t BPB_SecPerClus;
uint16_t BPB_RsvdSecCnt;
uint8_t BPB_NumFATs;
uint16_t BPB_RootEntCnt;
uint16_t BPB_TotSec16;
uint8_t BPB_Media;
uint16_t BPB_FATSz16;
uint16_t BPB_SecPerTrk;
uint16_t BPB_NumHeads;
uint32_t BPB_HiddSec;
uint32_t BPB_TotSec32;
uint32_t BPB_FATSz32;
uint16_t BPB_ExtFlags;
uint16_t BPB_FSVer;
uint32_t BPB_RootClus;
uint16_t BPB_FSInfo;
uint16_t BPB_BkBootSec;
uint8_t BPB_Reserved[12];
uint8_t BS_DrvNum;
uint8_t BS_Reserved1;
uint8_t BS_BootSig;
uint32_t BS_VolID;
char BS_VolLab[11];
char BS_FilSysType[8];
uint8_t Zeroes[420];
uint8_t Signature[2]; /* 0x55aa */
} __attribute__ ((packed));
union fat_bpb {
struct fat16_bpb fat16;
struct fat32_bpb fat32;
};
struct dir_entry {
char DIR_Name[11];
uint8_t DIR_Attr;
uint8_t DIR_NTRes;
uint8_t DIR_CrtTimeTenth;
uint16_t DIR_CrtTime;
uint16_t DIR_CrtDate;
uint16_t DIR_LstAccDate;
uint16_t DIR_FstClusHI;
uint16_t DIR_WrtTime;
uint16_t DIR_WrtDate;
uint16_t DIR_FstClusLO;
uint32_t DIR_FileSize;
} __attribute__ ((packed));
struct longfn_entry {
uint8_t LDIR_Ord;
char LDIR_Name1[10];
uint8_t LDIR_Attr;
uint8_t LDIR_Type;
uint8_t LDIR_Chksum;
char LDIR_Name2[12];
uint16_t LDIR_FstClusLO;
char LDIR_Name3[4];
} __attribute__ ((packed));
#define LAST_LONG_ENTRY 0x40
#define ATTR_READ_ONLY 0x01
#define ATTR_HIDDEN 0x02
#define ATTR_SYSTEM 0x04
#define ATTR_VOLUME_ID 0x08
#define ATTR_DIRECTORY 0x10
#define ATTR_ARCHIVE 0x20
#define ATTR_LONG_NAME (ATTR_READ_ONLY | ATTR_HIDDEN | ATTR_SYSTEM | ATTR_VOLUME_ID)
struct FSInfo {
uint8_t FSI_LeadSig[4]; /* 0x52 0x52 0x61 0x41 */
uint8_t FSI_Reserved1[480];
uint8_t FSI_StrucSig[4]; /* 0x72 0x72 0x41 0x61 */
uint32_t FSI_Free_Count;
uint32_t FSI_Nxt_Free;
uint8_t FSI_Reserved2[12];
uint8_t FSI_TrailSig[4]; /* 0x00 0x00 0x55 0xAA */
} __attribute__ ((packed));
#endif // DEVICEWRAPPERSTRUCTS_H