fat32.h File Reference

#include <sw_types.h>

Go to the source code of this file.

Classes
struct	lfn_entry
	Structure of the long file name slot. More...
struct	f_info
	Structure of a file containing its basic information required for many operations. More...
struct	file_stat
	Structure containing the basic details of a file/directory. More...

Macros
#define	END_OF_CLUSTER   0x0FFFFFFF
#define	END_OF_ROOT_CLUSTER   0X0FFFFFF8
#define	MAX_DIR_ENTRY_CNT   16
#define	FILE_SYS_TYPE_OFF   82
#define	BYTES_PER_SEC_OFF   11
#define	SEC_PER_CLUS_OFF   13
#define	RES_SEC_CNT_OFF   14
#define	FAT_CNT_OFF   16
#define	TOT_SEC_CNT_OFF   32
#define	SEC_PER_FAT   36
#define	ROOT_DIR_STRT_CLUS_OFF   44
#define	FS_INFOSECTOR_OFF   48
#define	BACKUP_BOOT_SEC_OFF   50
#define	NXT_FREE_CLUS_OFF   492
#define	FILE_SYS_TYPE_LENGTH   8
#define	SHRT_FILE_NAME_LEN   11
#define	STRT_CLUS_LOW_OFF   26
#define	STRT_CLUS_HIGH_OFF   20
#define	FILE_SIZE_OFF   28
#define	ATTR_OFF   11
#define	FILE_STAT_LEN   21
#define	CHECK_SUM_OFF   13
#define	FILE_NAME_SHRT_LEN   8
#define	FILE_NAME_EXTN_LEN   3
#define	LONG_FILE_NAME_LEN   255
#define	LOW_CLUSWORD_MASK   0x0000FFFF
#define	HIGH_CLUSWORD_MASK   0xFFFF0000
#define	LONG_FNAME_MASK   0x0F
#define	LAST_ORD_FIELD_SEQ   0x40
#define	LFN_END_MARK   0xFFFF
#define	LFN_TERM_MARK   0x0000
#define	LFN_FIRST_OFF   0x01
#define	LFN_SIXTH_OFF   0x0E
#define	LFN_TWELVETH_OFF   0x1C
#define	LFN_FIRST_SET_CNT   5
#define	LFN_SEC_SET_CNT   6
#define	LFN_THIRD_SET_CNT   2
#define	LFN_FIRST_SET_LEN   10
#define	LFN_SEC_SET_LEN   12
#define	LFN_THIRD_SET_LEN   4
#define	LFN_EMPTY_LEN   2
#define	LFN_LEN_PER_ENTRY   13
#define	FNAME_EXTN_SEP_OFF   6
#define	FNAME_SEQ_NUM_OFF   7
#define	BYTES_PER_CLUSTER_ENTRY   4
#define	DIR_ENTRY_LEN   32
#define	VOL_ID_LEN   4
#define	VOL_LABEL_LEN   11
#define	RESERV_LEN   12
#define	FS_VER_LEN   2
#define	OEM_NAME_LEN   8
#define	JUMP_INS_LEN   3
#define	MAX_FAT_CNT   2
#define	SPACE_VAL   32
#define	FILE_READ   0x01
#define	FILE_WRITE   0X02
#define	FILE_CREATE_NEW   0x04
#define	FILE_CREATE_ALWAYS   0x08
#define	FILE_APPEND   0x10
#define	ATTR_READ   0x01
#define	ATTR_HIDDEN   0x02
#define	ATTR_SYSTEM   0x04
#define	ATTR_VOL_LABEL   0x08
#define	ATTR_DIR   0x10
#define	ATTR_ARCHIVE   0x20
#define	ATTR_LONG_FNAME   0x0F
#define	FREE_DIR_ENTRY   0x00
#define	DEL_DIR_ENTRY   0xE5
#define	DOT_DIR_ENTRY   0x2E
#define	ASCII_DIFF   32
#define	FILE_SEEK_SET   0
#define	FILE_SEEK_CUR   1
#define	FILE_SEEK_END   2
#define	DELIMITER   '/'
#define	EXTN_DELIMITER   '.'
#define	TILDE   '~'
#define	FULL_SHRT_NAME_LEN   13

Typedefs
typedef struct f_info	file_info

Functions
struct	__attribute__ ((__packed__))
	Structure of the boot sector. More...
int	mount_file_system (u8 *dev)
	Mount the FAT file system and retrieve its basic information. More...
bool	chk_fat32_file_system (u8 *file_sys_type)
	Verify the type of FAT file system. More...
void	cal_region_offsets (boot_sector *bs, u8 *dev)
	Function to calculate all the region offsets. More...
int	file_open (const char *file_path, int flags)
	Function to open a specific file mentioned in the path based on the incoming modes. More...
bool	get_dir_entry (char *fname, dir_entry **entry, u8 *strt, u32 strt_clus, bool is_lfn)
	Function to check whether a given file name exists in the file system and if so retrieve the corresponding short file name directory entry. More...
int	lfn_entry_to_name (lfn_entry *entry, char *lfname, int *index)
	Function to get the long file name correspoding to a directory slot. More...
u8 *	cluster_to_memory_addr (u32 cluster)
	Function to get the corresponding physical address from the given cluster. More...
int	retrieve_file_info (file_info *finfo, dir_entry *entry, u8 mode, u8 *dir_offset, const char *path)
	Function to assign a file descriptor and necessary information to a file structure inorder to pursue subsequent operations. More...
u32	get_fat_table_entry (u32 cluster)
	Function to retrieve the next cluster value in a cluster chain from the FAT table. More...
void	convert_to_uppercase (char *file_name)
	Function to convert the incoming short file name to its corresponding upper case letters. More...
int	find_depth (const char *file_path)
	Function to calculate the number of iterations needed to reach the file from the given starting path. More...
int	create_file (char *lfname, char *shrt_name, u32 clus, dir_entry **entry)
	Function to create a file if the file doesnt exists and the create flag is set. More...
int	file_read (int fd, char *buffer, int bytes_to_read)
	Function to read the contents of a file. More...
int	file_write (int fd, const char *buffer, int bytes_to_write)
	Function to write into the given file with the contents given. More...
u32	allocate_cluster ()
	Function to find an unused cluster from the FAT table. More...
void	write_fat_table (u32 cluster, u32 value)
	Function to write into the FAT table after assigning an empty cluster to a file. More...
void	get_short_file_name (char *lfname, char *sfname, char seq_num)
	Function to extract the short file name given its long file name. More...
void	fill_lng_fname_entries (char *fname, u8 *entry, u8 chk_sum, int count)
	Function to put the long file name entries into the respective allocated region. More...
u8	calc_check_sum (u8 *dir_entry)
	Function to calculate the checksum for the long file name based on its short name entry. More...
int	file_close (int fd)
	Close the opened file based on the file descriptor and free the file structure pointer. More...
int	file_seek (int fd, int offset, int whence)
	Function to seek the opened file pointer to the desired location so that subsequent read and write operations are performed from the new value. More...
int	get_seek_off (file_info *file_ptr, u32 strt_cluster, int offset)
	Function to move the current cluster and its offset value to the value specified in the offset from the starting cluster provided. More...
int	get_long_file_name (char *fname, u8 **dir_strt, int *count)
	Function to retrieve the long file name given its end of the long file name entry. More...
int	file_rename (const char *old, const char *new)
	Function to rename a file/directory. More...
int	create_dir (const char *path)
	Function to create a directory. More...
int	chk_file_lock (const char *path)
file_stat *	read_dir (int fd)
int	open_dir (const char *path)
	Function to open a directory. More...
int	cal_req_dir_cnt (int file_name_len)
int	file_truncate (const char *tr_pf, int tr_lgh)
	file_truncate - function cause the regular file named by path to be truncated to a size of precisely length bytes More...
int	file_remove (const char *fl_name)
	file_remove - Deletes the file whose name is specified in filename More...
int	file_unlink (const char *ul_name)
	file_remove - Deletes the file whose name is specified in filename More...
int	list_dir (const char *path)
	Function to list the directory contents. More...

Variables
	boot_sector
	dir_entry

Macro Definition Documentation

#define ASCII_DIFF   32

#define ATTR_ARCHIVE   0x20

#define ATTR_DIR   0x10

#define ATTR_HIDDEN   0x02

#define ATTR_LONG_FNAME   0x0F

#define ATTR_OFF   11

#define ATTR_READ   0x01

#define ATTR_SYSTEM   0x04

#define ATTR_VOL_LABEL   0x08

#define BACKUP_BOOT_SEC_OFF   50

#define BYTES_PER_CLUSTER_ENTRY   4

#define BYTES_PER_SEC_OFF   11

#define CHECK_SUM_OFF   13

#define DEL_DIR_ENTRY   0xE5

#define DELIMITER   '/'

#define DIR_ENTRY_LEN   32

#define DOT_DIR_ENTRY   0x2E

#define END_OF_CLUSTER   0x0FFFFFFF

#define END_OF_ROOT_CLUSTER   0X0FFFFFF8

#define EXTN_DELIMITER   '.'

#define FAT_CNT_OFF   16

#define FILE_APPEND   0x10

#define FILE_CREATE_ALWAYS   0x08

#define FILE_CREATE_NEW   0x04

#define FILE_NAME_EXTN_LEN   3

#define FILE_NAME_SHRT_LEN   8

#define FILE_READ   0x01

#define FILE_SEEK_CUR   1

#define FILE_SEEK_END   2

#define FILE_SEEK_SET   0

#define FILE_SIZE_OFF   28

#define FILE_STAT_LEN   21

#define FILE_SYS_TYPE_LENGTH   8

#define FILE_SYS_TYPE_OFF   82

#define FILE_WRITE   0X02

#define FNAME_EXTN_SEP_OFF   6

#define FNAME_SEQ_NUM_OFF   7

#define FREE_DIR_ENTRY   0x00

#define FS_INFOSECTOR_OFF   48

#define FS_VER_LEN   2

#define FULL_SHRT_NAME_LEN   13

#define HIGH_CLUSWORD_MASK   0xFFFF0000

#define JUMP_INS_LEN   3

#define LAST_ORD_FIELD_SEQ   0x40

#define LFN_EMPTY_LEN   2

#define LFN_END_MARK   0xFFFF

#define LFN_FIRST_OFF   0x01

#define LFN_FIRST_SET_CNT   5

#define LFN_FIRST_SET_LEN   10

#define LFN_LEN_PER_ENTRY   13

#define LFN_SEC_SET_CNT   6

#define LFN_SEC_SET_LEN   12

#define LFN_SIXTH_OFF   0x0E

#define LFN_TERM_MARK   0x0000

#define LFN_THIRD_SET_CNT   2

#define LFN_THIRD_SET_LEN   4

#define LFN_TWELVETH_OFF   0x1C

#define LONG_FILE_NAME_LEN   255

#define LONG_FNAME_MASK   0x0F

#define LOW_CLUSWORD_MASK   0x0000FFFF

#define MAX_DIR_ENTRY_CNT   16

#define MAX_FAT_CNT   2

#define NXT_FREE_CLUS_OFF   492

#define OEM_NAME_LEN   8

#define RES_SEC_CNT_OFF   14

#define RESERV_LEN   12

#define ROOT_DIR_STRT_CLUS_OFF   44

#define SEC_PER_CLUS_OFF   13

#define SEC_PER_FAT   36

#define SHRT_FILE_NAME_LEN   11

#define SPACE_VAL   32

#define STRT_CLUS_HIGH_OFF   20

#define STRT_CLUS_LOW_OFF   26

#define TILDE   '~'

#define TOT_SEC_CNT_OFF   32

#define VOL_ID_LEN   4

#define VOL_LABEL_LEN   11

Typedef Documentation

typedef struct f_info file_info

Function Documentation

struct __attribute__

(

(__packed__)

)

Structure of the boot sector.

Structure of the 32 byte directory entry.

u32 allocate_cluster

(

)

Function to find an unused cluster from the FAT table.

Returns

Newly allocated cluster for the file

void cal_region_offsets	(	boot_sector *	bs,
		u8 *	dev
	)

Function to calculate all the region offsets.

Parameters

bs	Pointer to the boot sector structure which holds the information of the boot sector of the file system
dev	Pointer to the start of the file system

int cal_req_dir_cnt

(

int

file_name_len

)

Parameters

file_name_len

Returns

u8 calc_check_sum

(

u8 *

dir_entry

)

Function to calculate the checksum for the long file name based on its short name entry.

Parameters

dir_entry

Pointer to the start of the short file name corresponding to a long file name

Returns

checksum value of the short file name

bool chk_fat32_file_system

(

u8 *

file_sys_type

)

Verify the type of FAT file system.

Parameters

file_sys_type

Pointer to the location where the type of file system is stored

Returns

true:indicates FAT32 file system false:indicates not FAT32 file system

int chk_file_lock

(

const char *

path

)

Parameters

path

Returns

u8* cluster_to_memory_addr

(

u32

cluster

)

Function to get the corresponding physical address from the given cluster.

Parameters

cluster

Cluster value for which the address is to be obtained

Returns

Memory address of the incoming cluster

void convert_to_uppercase

(

char *

file_name

)

Function to convert the incoming short file name to its corresponding upper case letters.

Parameters

file_name

File name whose values are to be converted

int create_dir

(

const char *

path

)

Function to create a directory.

Parameters

path	Pointer to the start of the path which represents the directory hierarchy

Returns

On successful creation:File descriptor of the directory -1:If the creation failed or if it already exists

int create_file	(	char *	lfname,
		char *	shrt_name,
		u32	clus,
		dir_entry **	entry
	)

Function to create a file if the file doesnt exists and the create flag is set.

Parameters

lfname	Pointer to the start of the long file. NULL in case of short file name creation
shrt_name	Pointer to the start of the short file name. In case of long file names the corresponding short file name is found out.
clus	Starting cluster of the directory in which the file is going to be created
entry	Pointer to a pointer of the directory entry structure in which the short file name directory entry content is to be stored

Returns

On successful creation returns zero

int file_close

(

int

fd

)

Close the opened file based on the file descriptor and free the file structure pointer.

Parameters

fd	File descriptor of the file which needs to be closed

Returns

Zero on successful closing of the file

int file_open	(	const char *	file_path,
		int	flags
	)

Function to open a specific file mentioned in the path based on the incoming modes.

Parameters

file_path	Pointer to the location of the file path string
flags	Flags indicating the modes in which the file is to be opened

Returns

Non-zero:File descriptor of the opened file Zero :File open is unsuccessful

int file_read	(	int	fd,
		char *	buffer,
		int	bytes_to_read
	)

Function to read the contents of a file.

Parameters

fd	File descriptor of the file in which read operation needs to be performed
buffer	Pointer to the start of the buffer where the contents read are stored
bytes_to_read	Number of bytes to be read from the file

Returns

Number of bytes successfully read

int file_remove

(

const char *

fl_name

)

file_remove - Deletes the file whose name is specified in filename

Parameters

fl_name

- string containing the name of the file to be deleted

Returns

- if the file is successfully deleted, a zero value is returned. On failure, a non-zero value is returned

int file_rename	(	const char *	old,
		const char *	new
	)

Function to rename a file/directory.

Parameters

old	Constant pointer to the start of the path where the file which needs to be renamed is located
new	Constant pointer to the start of the path where the new name of the file/directory is situated

Returns

zero on successful renaming -1 if the new name already exists

int file_seek	(	int	fd,
		int	offset,
		int	whence
	)

Function to seek the opened file pointer to the desired location so that subsequent read and write operations are performed from the new value.

Parameters

fd	File descriptor of the file in which the seek operation needs to be performed
offset	Offset bytes indicating the number of bytes which needs to be moved
whence	Flag denoting the position from which the seek operation needs to be performed

Returns

Number of bytes traversed from the beginning of the file to the current position

int file_truncate	(	const char *	tr_pf,
		int	tr_lgh
	)

file_truncate - function cause the regular file named by path to be truncated to a size of precisely length bytes

Parameters

tr_pf	- truncates the file whose name is specified in filename
tr_lgh	- The desired truncate size of the file in bytes

Returns

- If the file contents is successfully truncated, a zero value is returned.On failure, non-Zero is returned

int file_unlink

(

const char *

ul_name

)

file_remove - Deletes the file whose name is specified in filename

Parameters

ul_name

- string containing the name of the file to be deleted

Returns

if the file is successfully deleted, a zero value is returned. On failure, a non-zero value is returned

file_remove - Deletes the file whose name is specified in filename

Parameters

ul_name

- string containing the name of the file to be deleted

Returns

- if the file is successfully deleted, a zero value is returned. On failure, a non-zero value is returned

int file_write	(	int	fd,
		const char *	buffer,
		int	bytes_to_write
	)

Function to write into the given file with the contents given.

Parameters

fd	File descriptor of the file
buffer	Pointer to the start of the contents which needs to be written into the file
bytes_to_write	Indicates the number of bytes which needs to be written into the file

Returns

Integer representing number of bytes successfully written into the file

void fill_lng_fname_entries	(	char *	fname,
		u8 *	entry,
		u8	chk_sum,
		int	count
	)

Function to put the long file name entries into the respective allocated region.

Parameters

fname	Pointer to the start of the long file name
entry	Starting memory location to the short file name directory entry
chk_sum	Calculated check sum of the short file name corresponding to the long file name
count	Counter indicating the number of 32 byte entries needed for the whole file name to get accommodated

int find_depth

(

const char *

file_path

)

Function to calculate the number of iterations needed to reach the file from the given starting path.

Parameters

file_path

Pointer to the starting of the file path

Returns

Count of directories which resides before the file/directory from the given path

bool get_dir_entry	(	char *	fname,
		dir_entry **	entry,
		u8 *	strt,
		u32	strt_clus,
		bool	is_lfn
	)

Function to check whether a given file name exists in the file system and if so retrieve the corresponding short file name directory entry.

Parameters

fname	Pointer to the start of the file name which needs to be searched
entry	Pointer to a pointer of the directory entry structure in which the short file name directory entry content is to be stored
strt	Pointer to the start of the region where the file/directory needs to be searched
strt_clus	Starting cluster of the directory in which the file is assumed to be present
is_lfn	Boolean value which indicates whether the file is short or long file

Returns

true: if the file/dir is present false:if it is not present in the respected path

u32 get_fat_table_entry

(

u32

cluster

)

Function to retrieve the next cluster value in a cluster chain from the FAT table.

Parameters

cluster

Cluster whose next cluster value is to be obtained

Returns

Corresponding FAT table entry for the given cluster

int get_long_file_name	(	char *	fname,
		u8 **	dir_strt,
		int *	count
	)

Function to retrieve the long file name given its end of the long file name entry.

Parameters

fname	Pointer to a location where the retrieved long file name starts
dir_strt	Pointer to the memory location where the last component of the long file name resides
count	Count representing the number of directory entries needed for the long file name

Returns

Length of the long file name

int get_seek_off	(	file_info *	file_ptr,
		u32	strt_cluster,
		int	offset
	)

Function to move the current cluster and its offset value to the value specified in the offset from the starting cluster provided.

Parameters

file_ptr	File structure pointer pointing to the opened file
strt_cluster	Starting cluster value from which the seek operation has to be performed
offset	Offset bytes for the seek operation

Returns

Number of bytes traversed from the beginning of the file

void get_short_file_name	(	char *	lfname,
		char *	sfname,
		char	seq_num
	)

Function to extract the short file name given its long file name.

Parameters

lfname	: Pointer to the start of the long file name string
sfname	: Pointer to the start of the short file name in which this function extracts and stored the short file name value
seq_num	: sequence number

int lfn_entry_to_name	(	lfn_entry *	entry,
		char *	lfname,
		int *	index
	)

Function to get the long file name correspoding to a directory slot.

Parameters

entry	Pointer to the slot where a long file component resides
lfname	Pointer to the start of the long file name
index	Pointer to the offset of the long file name where the retrieved name from the given slot is going to be stored

Returns

0:if the file name doesnt end in the given slot 1:if the file name ends in the given slot

int list_dir

(

const char *

path

)

Function to list the directory contents.

Parameters

path	Pointer to the start of the path representing the directory hierarchy

Returns

Number of directories/files present in the given directory

int mount_file_system

(

u8 *

dev

)

Mount the FAT file system and retrieve its basic information.

Parameters

dev	Pointer to the start of the file system image

Returns

0:File system is FAT32 and the mount process is successful -1:Mount is unsuccessful

int open_dir

(

const char *

path

)

Function to open a directory.

Parameters

path	Pointer to the start of the path representing the directory hierarchy

Returns

file descriptor assigned to the directory

file_stat* read_dir

(

int

fd

)

Parameters

fd

Returns

int retrieve_file_info	(	file_info *	finfo,
		dir_entry *	entry,
		u8	mode,
		u8 *	dir_offset,
		const char *	path
	)

Function to assign a file descriptor and necessary information to a file structure inorder to pursue subsequent operations.

Parameters

finfo	: Pointer to a file structure where the file information is stored
entry	: Pointer to the directory entry of the file/directory
mode	: Mode in which the file is requested to be opened
dir_offset	: directory offset
path	: path

Returns

returns : File descriptor of the file

void write_fat_table	(	u32	cluster,
		u32	value
	)

Function to write into the FAT table after assigning an empty cluster to a file.

Parameters

cluster	Cluster number for which the entry has to be made
value	Next cluster value of the cluster number provided

Variable Documentation

boot_sector

dir_entry