Device Virtual File System

Collaboration diagram for Device Virtual File System:

Modules
	File Descriptor
	File System API
	File API
	File POSIX API

Functions
rt_err_t	dfs_file_lock (void)
void	dfs_file_unlock (void)
int	dfs_init (void)
struct dfs_file *	dfs_file_create (void)
void	dfs_file_destroy (struct dfs_file *file)
void	fdt_fd_release (struct dfs_fdtable *fdt, int fd)
int	fdt_fd_associate_file (struct dfs_fdtable *fdt, int fd, struct dfs_file *file)
int	fd_new (void)
struct dfs_file *	fd_get (int fd)
struct dfs_fdtable *	dfs_fdtable_get (void)
struct dfs_fdtable *	dfs_fdtable_get_global (void)
int	dfs_fdtable_dup (struct dfs_fdtable *fdt_dst, struct dfs_fdtable *fdt_src, int fd_src)
int	dfs_fdtable_drop_fd (struct dfs_fdtable *fdt, int fd)
int	dfs_dup (int oldfd, int startfd)
int	dfs_dup_to (int oldfd, struct dfs_fdtable *fdtab)
int	dfs_dup_from (int oldfd, struct dfs_fdtable *fdtab)
int	sys_dup (int oldfd)
rt_err_t	sys_dup2 (int oldfd, int newfd)
const char *	dfs_subdir (const char *directory, const char *filename)
char *	dfs_normalize_path (const char *directory, const char *filename)
int	list_fd (void)
int	dfs_fd_dump (int argc, char **argv)

Detailed Description

DFS is a virtual file system in RT-Thread RTOS.

The DFS (Device Virtual File System) is a vfs file system of RT-Thread RTOS, which is focused on embedded device. VFS is an abstraction layer on top of a more concrete file system. The purpose of a VFS is to allow client applications to access different types of concrete file systems in a uniform way.

Figure 4: Device Virtual File System Architecture

The DFS specifies an interface between the kernel and a concrete file system. Therefore, it is easy to add support for new file system types to the kernel simply by fulfilling the interface.

Function Documentation

dfs_file_lock()

rt_err_t dfs_file_lock

(

void

)

Lock the file descriptor table mutex.

Returns

rt_err_t RT_EOK if lock acquired successfully, -RT_ENOSYS if filesystem not initialized, -RT_EBUSY if mutex is already locked (retries until acquired)

Note

This function will block indefinitely until the lock is acquired. Should not be called from interrupt service routines.

dfs_file_unlock()

void dfs_file_unlock

(

void

)

Unlock the file descriptor table mutex.

Note

This function releases the lock acquired by dfs_file_lock(). Should be called in the same context as the corresponding lock. Should not be called from interrupt service routines.

dfs_init()

int dfs_init

(

void

)

this function will initialize device file system.

dfs_file_create()

struct dfs_file* dfs_file_create

(

void

)

Create and initialize a new file descriptor structure.

Returns

struct dfs_file* Pointer to the newly created file descriptor structure, NULL if memory allocation failed

dfs_file_destroy()

void dfs_file_destroy

(

struct dfs_file *

file

)

Destroy and free a file descriptor structure.

Parameters

[in]

file

Pointer to the file descriptor structure to be destroyed

fdt_fd_release()

void fdt_fd_release	(	struct dfs_fdtable *	fdt,
		int	fd
	)

Release a file descriptor from the file descriptor table.

Parameters

[in,out]	fdt	Pointer to the file descriptor table
[in]	fd	The file descriptor to be released

fdt_fd_associate_file()

int fdt_fd_associate_file	(	struct dfs_fdtable *	fdt,
		int	fd,
		struct dfs_file *	file
	)

Associate a file structure with a file descriptor in the file descriptor table.

Parameters

[in,out]	fdt	Pointer to the file descriptor table
[in]	fd	The file descriptor to associate with
[in]	file	Pointer to the file structure to associate

Returns

int The file descriptor if successful (>= 0), -1 if association failed (invalid parameters or fd already in use), -RT_ENOSYS if filesystem lock failed

fd_new()

int fd_new

(

void

)

Allocate a new file descriptor in current process's file descriptor table.

Returns

int The allocated file descriptor index if successful (>= 0), -1 if allocation failed

fd_get()

struct dfs_file* fd_get

(

int

fd

)

Get file structure by file descriptor from current process's fd table.

Parameters

[in]

fd

The file descriptor to lookup

Returns

struct dfs_file* Pointer to the file structure if found, NULL if invalid fd or file not found

dfs_fdtable_get()

struct dfs_fdtable* dfs_fdtable_get

(

void

)

This function will get the file descriptor table of current process.

dfs_fdtable_get_global()

struct dfs_fdtable* dfs_fdtable_get_global

(

void

)

Get the global file descriptor table.

Returns

struct dfs_fdtable* Pointer to the global file descriptor table

dfs_fdtable_dup()

int dfs_fdtable_dup	(	struct dfs_fdtable *	fdt_dst,
		struct dfs_fdtable *	fdt_src,
		int	fd_src
	)

Dup the specified fd_src from fdt_src to fdt_dst.

Parameters

[out]	fdt_dst	is the fd table for destination, if empty, use global (_fdtab).
[in]	fdt_src	is the fd table for source, if empty, use global (_fdtab).
[in]	fd_src	is the fd in the designate fdt_src table.

Returns

-1 on failed or the allocated file descriptor.

dfs_fdtable_drop_fd()

int dfs_fdtable_drop_fd	(	struct dfs_fdtable *	fdt,
		int	fd
	)

drop fd from the fd table.

Parameters

fdt	is the fd table, if empty, use global (_fdtab).
fd	is the fd in the designate fd table.

Returns

-1 on failed the drop file descriptor.

dfs_dup()

int dfs_dup	(	int	oldfd,
		int	startfd
	)

Duplicate a file descriptor in the current process's file descriptor table.

Parameters

[in]	oldfd	The file descriptor to duplicate
[in]	startfd	The starting index to search for an available file descriptor slot

Returns

int The new file descriptor if successful (>=0), -1 if failed (invalid fd or allocation failed), -RT_ENOSYS if filesystem lock failed

dfs_dup_to()

int dfs_dup_to	(	int	oldfd,
		struct dfs_fdtable *	fdtab
	)

Duplicate a file descriptor from current process to target file descriptor table.

Parameters

[in]	oldfd	is the fd in current process.
[in,out]	fdtab	is the fd table to dup, if empty, use global (_fdtab).

Returns

-1 on failed or the allocated file descriptor.

dfs_dup_from()

int dfs_dup_from	(	int	oldfd,
		struct dfs_fdtable *	fdtab
	)

Duplicate a file descriptor from source table to current process.

Parameters

[in]	oldfd	is the fd in the designate fd table.
[in,out]	fdtab	is the fd table for oldfd, if empty, use global (_fdtab).

Returns

-1 on failed or the allocated file descriptor.

sys_dup()

int sys_dup

(

int

oldfd

)

System call to duplicate a file descriptor.

Parameters

[in]

oldfd

The file descriptor to duplicate

Returns

sysret_t/int The new file descriptor if successful (>=0), negative error code if failed

sys_dup2()

rt_err_t sys_dup2	(	int	oldfd,
		int	newfd
	)

System call to duplicate a file descriptor to a specific descriptor number.

Parameters

[in]	oldfd	The file descriptor to duplicate
[in]	newfd	The desired file descriptor number

Returns

rt_err_t The new file descriptor number if successful (>=0), -RT_ENOSYS if filesystem lock failed, -1 if operation failed (invalid descriptors or allocation failed)

dfs_subdir()

const char* dfs_subdir	(	const char *	directory,
		const char *	filename
	)

Get the subdirectory path relative to a parent directory.

Parameters

[in]	directory	The parent directory path
[in]	filename	The full path including parent directory and subpath

Returns

const char* Pointer to the subdirectory portion of filename, NULL if paths are identical or invalid

dfs_normalize_path()

char* dfs_normalize_path	(	const char *	directory,
		const char *	filename
	)

Normalize a path by combining directory and filename into an absolute path.

Parameters

[in]	directory	The parent directory path (NULL means use working directory)
[in]	filename	The filename or relative path to be normalized

Returns

char* The normalized absolute path (must be freed by caller), NULL if path is invalid or memory allocation fails

Note

This function will:

• Handle working directory when directory is NULL
• Join directory and filename with proper separators
• Resolve . and .. in paths
• Remove redundant slashes
• Ensure path starts with /
• Allocate memory for the returned path string

list_fd()

int list_fd

(

void

)

List all open file descriptors in the current process.

Returns

int 0 on success, -1 if failed to get file descriptor table

dfs_fd_dump()

int dfs_fd_dump	(	int	argc,
		char **	argv
	)

Dump all file descriptors information in the global file descriptor table.

Parameters

[in]	argc	Number of command line arguments (unused)
[in]	argv	Array of command line arguments (unused)

Returns

int 0 on success, -RT_ENOSYS if failed to acquire file system lock