Virtual Filesystem Component

Overview

Virtual filesystem (VFS) component provides a unified interface for drivers which can perform operations on file-like objects. These can be real filesystems (FAT, SPIFFS, etc.) or device drivers which provide a file-like interface.

This component allows C library functions, such as fopen and fprintf, to work with FS drivers. At a high level, each FS driver is associated with some path prefix. When one of C library functions needs to open a file, the VFS component searches for the FS driver associated with the file path and forwards the call to that driver. VFS also forwards read, write, and other calls for the given file to the same FS driver.

For example, one can register a FAT filesystem driver with the /fat prefix and call fopen("/fat/file.txt", "w"). Then the VFS component calls the function open of the FAT driver and pass the argument /file.txt to it together with appropriate mode flags. All subsequent calls to C library functions for the returned FILE* stream will also be forwarded to the FAT driver.

FS Registration

To register an FS driver, an application needs to define an instance of the esp_vfs_t structure and populate it with function pointers to FS APIs:

esp_vfs_t myfs = {
    .flags = ESP_VFS_FLAG_DEFAULT,
    .write = &myfs_write,
    .open = &myfs_open,
    .fstat = &myfs_fstat,
    .close = &myfs_close,
    .read = &myfs_read,
};

ESP_ERROR_CHECK(esp_vfs_register("/data", &myfs, NULL));

Depending on the way how the FS driver declares its API functions, either read, write, etc., or read_p, write_p, etc., should be used.

Case 1: API functions are declared without an extra context pointer (the FS driver is a singleton):

ssize_t myfs_write(int fd, const void * data, size_t size);

// In definition of esp_vfs_t:
    .flags = ESP_VFS_FLAG_DEFAULT,
    .write = &myfs_write,
// ... other members initialized

// When registering FS, context pointer (the third argument) is NULL:
ESP_ERROR_CHECK(esp_vfs_register("/data", &myfs, NULL));

Case 2: API functions are declared with an extra context pointer (the FS driver supports multiple instances):

ssize_t myfs_write(myfs_t* fs, int fd, const void * data, size_t size);

// In definition of esp_vfs_t:
    .flags = ESP_VFS_FLAG_CONTEXT_PTR,
    .write_p = &myfs_write,
// ... other members initialized

// When registering FS, pass the FS context pointer into the third argument
// (hypothetical myfs_mount function is used for illustrative purposes)
myfs_t* myfs_inst1 = myfs_mount(partition1->offset, partition1->size);
ESP_ERROR_CHECK(esp_vfs_register("/data1", &myfs, myfs_inst1));

// Can register another instance:
myfs_t* myfs_inst2 = myfs_mount(partition2->offset, partition2->size);
ESP_ERROR_CHECK(esp_vfs_register("/data2", &myfs, myfs_inst2));

Synchronous Input/Output Multiplexing

Synchronous input/output multiplexing by select() is supported in the VFS component. The implementation works in the following way.

select() is called with file descriptors which could belong to various VFS drivers.
The file descriptors are divided into groups each belonging to one VFS driver.
The file descriptors belonging to non-socket VFS drivers are handed over to the given VFS drivers by start_select(), described later on this page. This function represents the driver-specific implementation of select() for the given driver. This should be a non-blocking call which means the function should immediately return after setting up the environment for checking events related to the given file descriptors.
The file descriptors belonging to the socket VFS driver are handed over to the socket driver by socket_select() described later on this page. This is a blocking call which means that it will return only if there is an event related to socket file descriptors or a non-socket driver signals socket_select() to exit.
Results are collected from each VFS driver and all drivers are stopped by de-initialization of the environment for checking events.
The select() call ends and returns the appropriate results.

Non-Socket VFS Drivers

If you want to use select() with a file descriptor belonging to a non-socket VFS driver, then you need to register the driver with functions start_select() and end_select() similarly to the following example:

// In definition of esp_vfs_t:
    .start_select = &uart_start_select,
    .end_select = &uart_end_select,
// ... other members initialized

start_select() is called for setting up the environment for detection of read/write/error conditions on file descriptors belonging to the given VFS driver.

end_select() is called to stop/deinitialize/free the environment which was setup by start_select().

Note

end_select() might be called without a previous start_select() call in some rare circumstances. end_select() should fail gracefully if this is the case (i.e., should not crash but return an error instead).

Please refer to the reference implementation for the UART peripheral in esp_driver_uart/src/uart_vfs.c and most particularly to the functions uart_vfs_dev_register(), uart_start_select(), and uart_end_select() for more information.

Please check the following examples that demonstrate the use of select() with VFS file descriptors:

Socket VFS Drivers

A socket VFS driver is using its own internal implementation of select() and non-socket VFS drivers notify it upon read/write/error conditions.

A socket VFS driver needs to be registered with the following functions defined:

// In definition of esp_vfs_t:
    .socket_select = &lwip_select,
    .get_socket_select_semaphore = &lwip_get_socket_select_semaphore,
    .stop_socket_select = &lwip_stop_socket_select,
    .stop_socket_select_isr = &lwip_stop_socket_select_isr,
// ... other members initialized

socket_select() is the internal implementation of select() for the socket driver. It works only with file descriptors belonging to the socket VFS.

get_socket_select_semaphore() returns the signalization object (semaphore) which is used in non-socket drivers to stop the waiting in socket_select().

stop_socket_select() call is used to stop the waiting in socket_select() by passing the object returned by get_socket_select_semaphore().

stop_socket_select_isr() has the same functionality as stop_socket_select() but it can be used from ISR.

Please see lwip/port/esp32xx/vfs_lwip.c for a reference socket driver implementation using LWIP.

Note

If you use select() for socket file descriptors only then you can disable the CONFIG_VFS_SUPPORT_SELECT option to reduce the code size and improve performance.

You should not change the socket driver during an active select() call or you might experience some undefined behavior.

Paths

Each registered FS has a path prefix associated with it. This prefix can be considered as a "mount point" of this partition.

In case when mount points are nested, the mount point with the longest matching path prefix is used when opening the file. For instance, suppose that the following filesystems are registered in VFS:

FS 1 on /data
FS 2 on /data/static

Then:

FS 1 will be used when opening a file called /data/log.txt
FS 2 will be used when opening a file called /data/static/index.html
Even if /index.html" does not exist in FS 2, FS 1 will not be searched for /static/index.html.

As a general rule, mount point names must start with the path separator (/) and must contain at least one character after path separator. However, an empty mount point name is also supported and might be used in cases when an application needs to provide a "fallback" filesystem or to override VFS functionality altogether. Such filesystem will be used if no prefix matches the path given.

VFS does not handle dots (.) in path names in any special way. VFS does not treat .. as a reference to the parent directory. In the above example, using a path /data/static/../log.txt will not result in a call to FS 1 to open /log.txt. Specific FS drivers (such as FATFS) might handle dots in file names differently.

When opening files, the FS driver receives only relative paths to files. For example:

The myfs driver is registered with /data as a path prefix.
The application calls fopen("/data/config.json", ...).
The VFS component calls myfs_open("/config.json", ...).
The myfs driver opens the /config.json file.

VFS does not impose any limit on total file path length, but it does limit the FS path prefix to ESP_VFS_PATH_MAX characters. Individual FS drivers may have their own filename length limitations.

File Descriptors

File descriptors are small positive integers from 0 to FD_SETSIZE - 1, where FD_SETSIZE is defined in sys/select.h. The largest file descriptors (configured by CONFIG_LWIP_MAX_SOCKETS) are reserved for sockets. The VFS component contains a lookup-table called s_fd_table for mapping global file descriptors to VFS driver indexes registered in the s_vfs array.

Standard I/O streams (stdin, stdout, stderr) are mapped to file descriptors 0, 1, and 2 respectively. For more information on standard I/O, see Standard I/O and Console Output.

`eventfd()`

eventfd() call is a powerful tool to notify a select() based loop of custom events. The eventfd() implementation in ESP-IDF is generally the same as described in man(2) eventfd except for:

esp_vfs_eventfd_register() has to be called before calling eventfd()
Options EFD_CLOEXEC, EFD_NONBLOCK and EFD_SEMAPHORE are not supported in flags.
Option EFD_SUPPORT_ISR has been added in flags. This flag is required to read and write the eventfd in an interrupt handler.

Note that creating an eventfd with EFD_SUPPORT_ISR will cause interrupts to be temporarily disabled when reading, writing the file and during the beginning and the ending of the select() when this file is set.

Minified VFS

To minimize RAM usage, an alternative version of esp_vfs_register() function, esp_vfs_register_fs() is provided. This version accepts esp_vfs_fs_ops_t instead of esp_vfs_t alongside separate argument for OR-ed flags. Unlike esp_vfs_register(), it can handle statically allocated struct, as long as the ESP_VFS_FLAG_STATIC is provided.

The esp_vfs_fs_ops_t is split into separate structs based on features (directory operations, select support, termios support, ...). The main struct contains the basic functions (read, write, ...), alongside pointers to the feature-specific structs. These pointers can be NULL indicating lack of support for all the functions provided by that struct, which decreases the required memory.

Internally the VFS component uses this version of API, with additional steps to convert the esp_vfs_t to esp_vfs_fs_ops_t upon registration.

Well Known VFS Devices

IDF defines several VFS devices that can be used by applications. These devices are, among others:

/dev/uart/<UART NUMBER> - file mapping to an UART opened with the VFS driver. The UART number is the number of the UART peripheral.

/dev/null - file that discards all data written to it and returns EOF when read. It is automatically created if CONFIG_VFS_INITIALIZE_DEV_NULL is enabled.

/dev/console - file that is connected to the primary and secondary outputs specified in the menuconfig by CONFIG_ESP_CONSOLE_UART and CONFIG_ESP_CONSOLE_SECONDARY respectively. More information can be found here Standard I/O and Console Output.

Application Examples

system/eventfd demonstrates how to use eventfd() to collect events from tasks and ISRs in a select() based main loop, using two tasks and a timer ISR (interrupt service routine) callback.
system/select demonstrates how to use synchronous I/O multiplexing with the select() function, using UART and socket file descriptors, and configuring both to act as loopbacks to receive messages sent from other tasks.
storage/semihost_vfs demonstrates how to use the semihosting VFS driver, including registering a host directory, redirecting stdout from UART to a file on the host, and reading and printing the content of a text file.

API Reference

Header File

components/vfs/include/esp_vfs.h
This header file can be included with:
#include "esp_vfs.h"
This header file is a part of the API provided by the vfs component. To declare that your component depends on vfs, add the following to your CMakeLists.txt:
REQUIRES vfs
or
PRIV_REQUIRES vfs

Functions

ssize_t esp_vfs_write(struct _reent *r, int fd, const void *data, size_t size): These functions are to be used in newlib syscall table. They will be called by newlib when it needs to use any of the syscalls.

off_t esp_vfs_lseek(struct _reent *r, int fd, off_t size, int mode)

ssize_t esp_vfs_read(struct _reent *r, int fd, void *dst, size_t size)

int esp_vfs_open(struct _reent *r, const char *path, int flags, int mode)

int esp_vfs_close(struct _reent *r, int fd)

int esp_vfs_fstat(struct _reent *r, int fd, struct stat *st)

int esp_vfs_stat(struct _reent *r, const char *path, struct stat *st)

int esp_vfs_link(struct _reent *r, const char *n1, const char *n2)

int esp_vfs_unlink(struct _reent *r, const char *path)

int esp_vfs_rename(struct _reent *r, const char *src, const char *dst)

int esp_vfs_utime(const char *path, const struct utimbuf *times)

esp_err_t esp_vfs_register(const char *base_path, const esp_vfs_t *vfs, void *ctx)

Register a virtual filesystem for given path prefix.

Parameters

base_path -- file path prefix associated with the filesystem. Must be a zero-terminated C string, may be empty. If not empty, must be up to ESP_VFS_PATH_MAX characters long, and at least 2 characters long. Name must start with a "/" and must not end with "/". For example, "/data" or "/dev/spi" are valid. These VFSes would then be called to handle file paths such as "/data/myfile.txt" or "/dev/spi/0". In the special case of an empty base_path, a "fallback" VFS is registered. Such VFS will handle paths which are not matched by any other registered VFS.
vfs -- Pointer to esp_vfs_t, a structure which maps syscalls to the filesystem driver functions. VFS component doesn't assume ownership of this pointer.
ctx -- If vfs->flags has ESP_VFS_FLAG_CONTEXT_PTR set, a pointer which should be passed to VFS functions. Otherwise, NULL.

Returns

ESP_OK if successful, ESP_ERR_NO_MEM if too many VFSes are registered.

esp_err_t esp_vfs_register_fd_range(const esp_vfs_t *vfs, void *ctx, int min_fd, int max_fd)

Special case function for registering a VFS that uses a method other than open() to open new file descriptors from the interval <min_fd; max_fd).

This is a special-purpose function intended for registering LWIP sockets to VFS.

Parameters

vfs -- Pointer to esp_vfs_t. Meaning is the same as for esp_vfs_register().
ctx -- Pointer to context structure. Meaning is the same as for esp_vfs_register().
min_fd -- The smallest file descriptor this VFS will use.
max_fd -- Upper boundary for file descriptors this VFS will use (the biggest file descriptor plus one).

Returns

ESP_OK if successful, ESP_ERR_NO_MEM if too many VFSes are registered, ESP_ERR_INVALID_ARG if the file descriptor boundaries are incorrect.

esp_err_t esp_vfs_register_with_id(const esp_vfs_t *vfs, void *ctx, esp_vfs_id_t *vfs_id)

Special case function for registering a VFS that uses a method other than open() to open new file descriptors. In comparison with esp_vfs_register_fd_range, this function doesn't pre-registers an interval of file descriptors. File descriptors can be registered later, by using esp_vfs_register_fd.

Parameters

vfs -- Pointer to esp_vfs_t. Meaning is the same as for esp_vfs_register().
ctx -- Pointer to context structure. Meaning is the same as for esp_vfs_register().
vfs_id -- Here will be written the VFS ID which can be passed to esp_vfs_register_fd for registering file descriptors.

Returns

ESP_OK if successful, ESP_ERR_NO_MEM if too many VFSes are registered, ESP_ERR_INVALID_ARG if the file descriptor boundaries are incorrect.

esp_err_t esp_vfs_unregister(const char *base_path)

Unregister a virtual filesystem for given path prefix

Parameters: base_path -- file prefix previously used in esp_vfs_register call
Returns: ESP_OK if successful, ESP_ERR_INVALID_STATE if VFS for given prefix hasn't been registered

esp_err_t esp_vfs_unregister_with_id(esp_vfs_id_t vfs_id)

Unregister a virtual filesystem with the given index

Parameters: vfs_id -- The VFS ID returned by esp_vfs_register_with_id
Returns: ESP_OK if successful, ESP_ERR_INVALID_STATE if VFS for the given index hasn't been registered

esp_err_t esp_vfs_register_fd(esp_vfs_id_t vfs_id, int *fd)

Special function for registering another file descriptor for a VFS registered by esp_vfs_register_with_id. This function should only be used to register permanent file descriptors (socket fd) that are not removed after being closed.

Parameters

vfs_id -- VFS identificator returned by esp_vfs_register_with_id.
fd -- The registered file descriptor will be written to this address.

Returns

ESP_OK if the registration is successful, ESP_ERR_NO_MEM if too many file descriptors are registered, ESP_ERR_INVALID_ARG if the arguments are incorrect.

esp_err_t esp_vfs_register_fd_with_local_fd(esp_vfs_id_t vfs_id, int local_fd, bool permanent, int *fd)

Special function for registering another file descriptor with given local_fd for a VFS registered by esp_vfs_register_with_id.

Parameters

vfs_id -- VFS identificator returned by esp_vfs_register_with_id.
local_fd -- The fd in the local vfs. Passing -1 will set the local fd as the (*fd) value.
permanent -- Whether the fd should be treated as permannet (not removed after close())
fd -- The registered file descriptor will be written to this address.

Returns

ESP_OK if the registration is successful, ESP_ERR_NO_MEM if too many file descriptors are registered, ESP_ERR_INVALID_ARG if the arguments are incorrect.

esp_err_t esp_vfs_unregister_fd(esp_vfs_id_t vfs_id, int fd)

Special function for unregistering a file descriptor belonging to a VFS registered by esp_vfs_register_with_id.

Parameters

vfs_id -- VFS identificator returned by esp_vfs_register_with_id.
fd -- File descriptor which should be unregistered.

Returns

ESP_OK if the registration is successful, ESP_ERR_INVALID_ARG if the arguments are incorrect.

int esp_vfs_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout)

Synchronous I/O multiplexing which implements the functionality of POSIX select() for VFS.

Parameters

nfds -- Specifies the range of descriptors which should be checked. The first nfds descriptors will be checked in each set.
readfds -- If not NULL, then points to a descriptor set that on input specifies which descriptors should be checked for being ready to read, and on output indicates which descriptors are ready to read.
writefds -- If not NULL, then points to a descriptor set that on input specifies which descriptors should be checked for being ready to write, and on output indicates which descriptors are ready to write.
errorfds -- If not NULL, then points to a descriptor set that on input specifies which descriptors should be checked for error conditions, and on output indicates which descriptors have error conditions.
timeout -- If not NULL, then points to timeval structure which specifies the time period after which the functions should time-out and return. If it is NULL, then the function will not time-out. Note that the timeout period is rounded up to the system tick and incremented by one.

Returns

The number of descriptors set in the descriptor sets, or -1 when an error (specified by errno) have occurred.

void esp_vfs_select_triggered(esp_vfs_select_sem_t sem)

Notification from a VFS driver about a read/write/error condition.

This function is called when the VFS driver detects a read/write/error condition as it was requested by the previous call to start_select.

Parameters: sem -- semaphore structure which was passed to the driver by the start_select call

void esp_vfs_select_triggered_isr(esp_vfs_select_sem_t sem, BaseType_t *woken)

Notification from a VFS driver about a read/write/error condition (ISR version)

This function is called when the VFS driver detects a read/write/error condition as it was requested by the previous call to start_select.

Parameters

sem -- semaphore structure which was passed to the driver by the start_select call
woken -- is set to pdTRUE if the function wakes up a task with higher priority

ssize_t esp_vfs_pread(int fd, void *dst, size_t size, off_t offset)

Implements the VFS layer of POSIX pread()

Parameters

fd -- File descriptor used for read
dst -- Pointer to the buffer where the output will be written
size -- Number of bytes to be read
offset -- Starting offset of the read

Returns

A positive return value indicates the number of bytes read. -1 is return on failure and errno is set accordingly.

ssize_t esp_vfs_pwrite(int fd, const void *src, size_t size, off_t offset)

Implements the VFS layer of POSIX pwrite()

Parameters

fd -- File descriptor used for write
src -- Pointer to the buffer from where the output will be read
size -- Number of bytes to write
offset -- Starting offset of the write

Returns

A positive return value indicates the number of bytes written. -1 is return on failure and errno is set accordingly.

void esp_vfs_dump_fds(FILE *fp)

Dump the existing VFS FDs data to FILE* fp.

Dump the FDs in the format:

        <VFS Path Prefix>-<FD seen by App>-<FD seen by driver>

   where:
    VFS Path Prefix   : file prefix used in the esp_vfs_register call
    FD seen by App    : file descriptor returned by the vfs to the application for the path prefix
    FD seen by driver : file descriptor used by the driver for the same file prefix.

Parameters: fp -- File descriptor where data will be dumped

void esp_vfs_dump_registered_paths(FILE *fp)

Dump all registered FSs to the provided FILE*.

Dump the FSs in the format:

       <index>:<VFS Path Prefix> -> <VFS entry ptr>

   where:
       index           : internal index in the table of registered FSs (the same as returned when registering fd with id)
       VFS Path Prefix : file prefix used in the esp_vfs_register call or "NULL"
       VFS entry ptr   : pointer to the esp_vfs_fs_ops_t struct used internally when resolving the calls

Parameters: fp -- File descriptor where data will be dumped

Structures

struct esp_vfs_t

VFS definition structure.

This structure should be filled with pointers to corresponding FS driver functions.

VFS component will translate all FDs so that the filesystem implementation sees them starting at zero. The caller sees a global FD which is prefixed with an pre-filesystem-implementation.

Some FS implementations expect some state (e.g. pointer to some structure) to be passed in as a first argument. For these implementations, populate the members of this structure which have _p suffix, set flags member to ESP_VFS_FLAG_CONTEXT_PTR and provide the context pointer to esp_vfs_register function. If the implementation doesn't use this extra argument, populate the members without _p suffix and set flags member to ESP_VFS_FLAG_DEFAULT.

If the FS driver doesn't provide some of the functions, set corresponding members to NULL.

Public Members

int flags: ESP_VFS_FLAG_CONTEXT_PTR and/or ESP_VFS_FLAG_READONLY_FS or ESP_VFS_FLAG_DEFAULT

ssize_t (*write_p)(void *p, int fd, const void *data, size_t size): Write with context pointer

ssize_t (*write)(int fd, const void *data, size_t size): Write without context pointer

off_t (*lseek_p)(void *p, int fd, off_t size, int mode): Seek with context pointer

off_t (*lseek)(int fd, off_t size, int mode): Seek without context pointer

ssize_t (*read_p)(void *ctx, int fd, void *dst, size_t size): Read with context pointer

ssize_t (*read)(int fd, void *dst, size_t size): Read without context pointer

ssize_t (*pread_p)(void *ctx, int fd, void *dst, size_t size, off_t offset): pread with context pointer

ssize_t (*pread)(int fd, void *dst, size_t size, off_t offset): pread without context pointer

ssize_t (*pwrite_p)(void *ctx, int fd, const void *src, size_t size, off_t offset): pwrite with context pointer

ssize_t (*pwrite)(int fd, const void *src, size_t size, off_t offset): pwrite without context pointer

int (*open_p)(void *ctx, const char *path, int flags, int mode): open with context pointer

int (*open)(const char *path, int flags, int mode): open without context pointer

int (*close_p)(void *ctx, int fd): close with context pointer

int (*close)(int fd): close without context pointer

int (*fstat_p)(void *ctx, int fd, struct stat *st): fstat with context pointer

int (*fstat)(int fd, struct stat *st): fstat without context pointer

int (*stat_p)(void *ctx, const char *path, struct stat *st): stat with context pointer

int (*stat)(const char *path, struct stat *st): stat without context pointer

int (*link_p)(void *ctx, const char *n1, const char *n2): link with context pointer

int (*link)(const char *n1, const char *n2): link without context pointer

int (*unlink_p)(void *ctx, const char *path): unlink with context pointer

int (*unlink)(const char *path): unlink without context pointer

int (*rename_p)(void *ctx, const char *src, const char *dst): rename with context pointer

int (*rename)(const char *src, const char *dst): rename without context pointer

DIR *(*opendir_p)(void *ctx, const char *name): opendir with context pointer

DIR *(*opendir)(const char *name): opendir without context pointer

struct dirent *(*readdir_p)(void *ctx, DIR *pdir): readdir with context pointer

struct dirent *(*readdir)(DIR *pdir): readdir without context pointer

int (*readdir_r_p)(void *ctx, DIR *pdir, struct dirent *entry, struct dirent **out_dirent): readdir_r with context pointer

int (*readdir_r)(DIR *pdir, struct dirent *entry, struct dirent **out_dirent): readdir_r without context pointer

long (*telldir_p)(void *ctx, DIR *pdir): telldir with context pointer

long (*telldir)(DIR *pdir): telldir without context pointer

void (*seekdir_p)(void *ctx, DIR *pdir, long offset): seekdir with context pointer

void (*seekdir)(DIR *pdir, long offset): seekdir without context pointer

int (*closedir_p)(void *ctx, DIR *pdir): closedir with context pointer

int (*closedir)(DIR *pdir): closedir without context pointer

int (*mkdir_p)(void *ctx, const char *name, mode_t mode): mkdir with context pointer

int (*mkdir)(const char *name, mode_t mode): mkdir without context pointer

int (*rmdir_p)(void *ctx, const char *name): rmdir with context pointer

int (*rmdir)(const char *name): rmdir without context pointer

int (*fcntl_p)(void *ctx, int fd, int cmd, int arg): fcntl with context pointer

int (*fcntl)(int fd, int cmd, int arg): fcntl without context pointer

int (*ioctl_p)(void *ctx, int fd, int cmd, va_list args): ioctl with context pointer

int (*ioctl)(int fd, int cmd, va_list args): ioctl without context pointer

int (*fsync_p)(void *ctx, int fd): fsync with context pointer

int (*fsync)(int fd): fsync without context pointer

int (*access_p)(void *ctx, const char *path, int amode): access with context pointer

int (*access)(const char *path, int amode): access without context pointer

int (*truncate_p)(void *ctx, const char *path, off_t length): truncate with context pointer

int (*truncate)(const char *path, off_t length): truncate without context pointer

int (*ftruncate_p)(void *ctx, int fd, off_t length): ftruncate with context pointer

int (*ftruncate)(int fd, off_t length): ftruncate without context pointer

int (*utime_p)(void *ctx, const char *path, const struct utimbuf *times): utime with context pointer

int (*utime)(const char *path, const struct utimbuf *times): utime without context pointer

int (*tcsetattr_p)(void *ctx, int fd, int optional_actions, const struct termios *p): tcsetattr with context pointer

int (*tcsetattr)(int fd, int optional_actions, const struct termios *p): tcsetattr without context pointer

int (*tcgetattr_p)(void *ctx, int fd, struct termios *p): tcgetattr with context pointer

int (*tcgetattr)(int fd, struct termios *p): tcgetattr without context pointer

int (*tcdrain_p)(void *ctx, int fd): tcdrain with context pointer

int (*tcdrain)(int fd): tcdrain without context pointer

int (*tcflush_p)(void *ctx, int fd, int select): tcflush with context pointer

int (*tcflush)(int fd, int select): tcflush without context pointer

int (*tcflow_p)(void *ctx, int fd, int action): tcflow with context pointer

int (*tcflow)(int fd, int action): tcflow without context pointer

pid_t (*tcgetsid_p)(void *ctx, int fd): tcgetsid with context pointer

pid_t (*tcgetsid)(int fd): tcgetsid without context pointer

int (*tcsendbreak_p)(void *ctx, int fd, int duration): tcsendbreak with context pointer

int (*tcsendbreak)(int fd, int duration): tcsendbreak without context pointer

esp_err_t (*start_select)(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, esp_vfs_select_sem_t sem, void **end_select_args): start_select is called for setting up synchronous I/O multiplexing of the desired file descriptors in the given VFS

int (*socket_select)(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout): socket select function for socket FDs with the functionality of POSIX select(); this should be set only for the socket VFS

void (*stop_socket_select)(void *sem): called by VFS to interrupt the socket_select call when select is activated from a non-socket VFS driver; set only for the socket driver

void (*stop_socket_select_isr)(void *sem, BaseType_t *woken): stop_socket_select which can be called from ISR; set only for the socket driver

void *(*get_socket_select_semaphore)(void): end_select is called to stop the I/O multiplexing and deinitialize the environment created by start_select for the given VFS

esp_err_t (*end_select)(void *end_select_args): get_socket_select_semaphore returns semaphore allocated in the socket driver; set only for the socket driver

Macros

MAX_FDS: Maximum number of (global) file descriptors.

ESP_VFS_PATH_MAX: Maximum length of path prefix (not including zero terminator)

ESP_VFS_FLAG_DEFAULT: Default value of flags member in esp_vfs_t structure.

ESP_VFS_FLAG_CONTEXT_PTR: Flag which indicates that FS needs extra context pointer in syscalls.

ESP_VFS_FLAG_READONLY_FS: Flag which indicates that FS is located on read-only partition.

ESP_VFS_FLAG_STATIC: Flag which indicates that VFS structure should be freed upon unregistering.

Note

Free if false, do not free if true

Header File

components/vfs/include/esp_vfs_ops.h
This header file can be included with:
#include "esp_vfs_ops.h"
This header file is a part of the API provided by the vfs component. To declare that your component depends on vfs, add the following to your CMakeLists.txt:
REQUIRES vfs
or
PRIV_REQUIRES vfs

Functions

esp_err_t esp_vfs_register_fs(const char *base_path, const esp_vfs_fs_ops_t *vfs, int flags, void *ctx)

Register a virtual filesystem for given path prefix.

Parameters

base_path -- file path prefix associated with the filesystem. Must be a zero-terminated C string, may be empty. If not empty, must be up to ESP_VFS_PATH_MAX characters long, and at least 2 characters long. Name must start with a "/" and must not end with "/". For example, "/data" or "/dev/spi" are valid. These VFSes would then be called to handle file paths such as "/data/myfile.txt" or "/dev/spi/0". In the special case of an empty base_path, a "fallback" VFS is registered. Such VFS will handle paths which are not matched by any other registered VFS.
vfs -- Pointer to esp_vfs_fs_ops_t, a structure which maps syscalls to the filesystem driver functions. VFS component does not assume ownership of this struct, but see flags for more info
flags -- Set of binary flags controlling how the registered FS should be treated
- ESP_VFS_FLAG_STATIC - if this flag is specified VFS assumes the provided esp_vfs_fs_ops_t and all its subcomponents are statically allocated, if it is not enabled a deep copy of the provided struct will be created, which will be managed by the VFS component
- ESP_VFS_FLAG_CONTEXT_PTR - If set, the VFS will use the context-aware versions of the filesystem operation functions (suffixed with _p) in esp_vfs_fs_ops_t and its subcomponents. The ctx parameter will be passed as the context argument when these functions are invoked.
ctx -- Context pointer for fs operation functions, see the ESP_VFS_FLAG_CONTEXT_PTR. Should be NULL if not used.

Returns

ESP_OK if successful, ESP_ERR_NO_MEM if too many FSes are registered.

esp_err_t esp_vfs_register_fs_with_id(const esp_vfs_fs_ops_t *vfs, int flags, void *ctx, esp_vfs_id_t *id): Analog of esp_vfs_register_with_id which accepts esp_vfs_fs_ops_t instead.

esp_err_t esp_vfs_unregister_fs(const char *base_path): Alias for esp_vfs_unregister for naming consistency

esp_err_t esp_vfs_unregister_fs_with_id(esp_vfs_id_t id): Alias for esp_vfs_unregister_with_id for naming consistency

Structures

struct esp_vfs_select_sem_t

VFS semaphore type for select()

Public Members

bool is_sem_local: type of "sem" is SemaphoreHandle_t when true, defined by socket driver otherwise

void *sem: semaphore instance

struct esp_vfs_dir_ops_t

Struct containing function pointers to directory related functionality.

Public Members

int (*stat_p)(void *ctx, const char *path, struct stat *st): stat with context pointer

int (*stat)(const char *path, struct stat *st): stat without context pointer

int (*link_p)(void *ctx, const char *n1, const char *n2): link with context pointer

int (*link)(const char *n1, const char *n2): link without context pointer

int (*unlink_p)(void *ctx, const char *path): unlink with context pointer

int (*unlink)(const char *path): unlink without context pointer

int (*rename_p)(void *ctx, const char *src, const char *dst): rename with context pointer

int (*rename)(const char *src, const char *dst): rename without context pointer

DIR *(*opendir_p)(void *ctx, const char *name): opendir with context pointer

DIR *(*opendir)(const char *name): opendir without context pointer

struct dirent *(*readdir_p)(void *ctx, DIR *pdir): readdir with context pointer

struct dirent *(*readdir)(DIR *pdir): readdir without context pointer

int (*readdir_r_p)(void *ctx, DIR *pdir, struct dirent *entry, struct dirent **out_dirent): readdir_r with context pointer

int (*readdir_r)(DIR *pdir, struct dirent *entry, struct dirent **out_dirent): readdir_r without context pointer

long (*telldir_p)(void *ctx, DIR *pdir): telldir with context pointer

long (*telldir)(DIR *pdir): telldir without context pointer

void (*seekdir_p)(void *ctx, DIR *pdir, long offset): seekdir with context pointer

void (*seekdir)(DIR *pdir, long offset): seekdir without context pointer

int (*closedir_p)(void *ctx, DIR *pdir): closedir with context pointer

int (*closedir)(DIR *pdir): closedir without context pointer

int (*mkdir_p)(void *ctx, const char *name, mode_t mode): mkdir with context pointer

int (*mkdir)(const char *name, mode_t mode): mkdir without context pointer

int (*rmdir_p)(void *ctx, const char *name): rmdir with context pointer

int (*rmdir)(const char *name): rmdir without context pointer

int (*access_p)(void *ctx, const char *path, int amode): access with context pointer

int (*access)(const char *path, int amode): access without context pointer

int (*truncate_p)(void *ctx, const char *path, off_t length): truncate with context pointer

int (*truncate)(const char *path, off_t length): truncate without context pointer

int (*ftruncate_p)(void *ctx, int fd, off_t length): ftruncate with context pointer

int (*ftruncate)(int fd, off_t length): ftruncate without context pointer

int (*utime_p)(void *ctx, const char *path, const struct utimbuf *times): utime with context pointer

int (*utime)(const char *path, const struct utimbuf *times): utime without context pointer

struct esp_vfs_termios_ops_t

Struct containing function pointers to termios related functionality.

Public Members

int (*tcsetattr_p)(void *ctx, int fd, int optional_actions, const struct termios *p): tcsetattr with context pointer

int (*tcsetattr)(int fd, int optional_actions, const struct termios *p): tcsetattr without context pointer

int (*tcgetattr_p)(void *ctx, int fd, struct termios *p): tcgetattr with context pointer

int (*tcgetattr)(int fd, struct termios *p): tcgetattr without context pointer

int (*tcdrain_p)(void *ctx, int fd): tcdrain with context pointer

int (*tcdrain)(int fd): tcdrain without context pointer

int (*tcflush_p)(void *ctx, int fd, int select): tcflush with context pointer

int (*tcflush)(int fd, int select): tcflush without context pointer

int (*tcflow_p)(void *ctx, int fd, int action): tcflow with context pointer

int (*tcflow)(int fd, int action): tcflow without context pointer

pid_t (*tcgetsid_p)(void *ctx, int fd): tcgetsid with context pointer

pid_t (*tcgetsid)(int fd): tcgetsid without context pointer

int (*tcsendbreak_p)(void *ctx, int fd, int duration): tcsendbreak with context pointer

int (*tcsendbreak)(int fd, int duration): tcsendbreak without context pointer

struct esp_vfs_select_ops_t

Struct containing function pointers to select related functionality.

Public Members

esp_err_t (*start_select)(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, esp_vfs_select_sem_t sem, void **end_select_args): start_select is called for setting up synchronous I/O multiplexing of the desired file descriptors in the given VFS

int (*socket_select)(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout): socket select function for socket FDs with the functionality of POSIX select(); this should be set only for the socket VFS

void (*stop_socket_select)(void *sem): called by VFS to interrupt the socket_select call when select is activated from a non-socket VFS driver; set only for the socket driver

void (*stop_socket_select_isr)(void *sem, BaseType_t *woken): stop_socket_select which can be called from ISR; set only for the socket driver

void *(*get_socket_select_semaphore)(void): end_select is called to stop the I/O multiplexing and deinitialize the environment created by start_select for the given VFS

esp_err_t (*end_select)(void *end_select_args): get_socket_select_semaphore returns semaphore allocated in the socket driver; set only for the socket driver

struct esp_vfs_fs_ops_t

Main struct of the minified vfs API, containing basic function pointers as well as pointers to the other subcomponents.

Public Members

ssize_t (*write_p)(void *p, int fd, const void *data, size_t size): Write with context pointer

ssize_t (*write)(int fd, const void *data, size_t size): Write without context pointer

off_t (*lseek_p)(void *p, int fd, off_t size, int mode): Seek with context pointer

off_t (*lseek)(int fd, off_t size, int mode): Seek without context pointer

ssize_t (*read_p)(void *ctx, int fd, void *dst, size_t size): Read with context pointer

ssize_t (*read)(int fd, void *dst, size_t size): Read without context pointer

ssize_t (*pread_p)(void *ctx, int fd, void *dst, size_t size, off_t offset): pread with context pointer

ssize_t (*pread)(int fd, void *dst, size_t size, off_t offset): pread without context pointer

ssize_t (*pwrite_p)(void *ctx, int fd, const void *src, size_t size, off_t offset): pwrite with context pointer

ssize_t (*pwrite)(int fd, const void *src, size_t size, off_t offset): pwrite without context pointer

int (*open_p)(void *ctx, const char *path, int flags, int mode): open with context pointer

int (*open)(const char *path, int flags, int mode): open without context pointer

int (*close_p)(void *ctx, int fd): close with context pointer

int (*close)(int fd): close without context pointer

int (*fstat_p)(void *ctx, int fd, struct stat *st): fstat with context pointer

int (*fstat)(int fd, struct stat *st): fstat without context pointer

int (*fcntl_p)(void *ctx, int fd, int cmd, int arg): fcntl with context pointer

int (*fcntl)(int fd, int cmd, int arg): fcntl without context pointer

int (*ioctl_p)(void *ctx, int fd, int cmd, va_list args): ioctl with context pointer

int (*ioctl)(int fd, int cmd, va_list args): ioctl without context pointer

int (*fsync_p)(void *ctx, int fd): fsync with context pointer

int (*fsync)(int fd): fsync without context pointer

esp_vfs_dir_ops_t *dir: pointer to the dir subcomponent

esp_vfs_termios_ops_t *termios: pointer to the termios subcomponent

esp_vfs_select_ops_t *select: pointer to the select subcomponent

Type Definitions

typedef int esp_vfs_id_t

Header File

components/vfs/include/esp_vfs_dev.h
This header file can be included with:
#include "esp_vfs_dev.h"
This header file is a part of the API provided by the vfs component. To declare that your component depends on vfs, add the following to your CMakeLists.txt:
REQUIRES vfs
or
PRIV_REQUIRES vfs

Functions

void esp_vfs_dev_uart_register(void)

void esp_vfs_dev_uart_use_nonblocking(int uart_num)

void esp_vfs_dev_uart_use_driver(int uart_num)

int esp_vfs_dev_uart_port_set_rx_line_endings(int uart_num, esp_line_endings_t mode)

int esp_vfs_dev_uart_port_set_tx_line_endings(int uart_num, esp_line_endings_t mode)

void esp_vfs_dev_uart_set_rx_line_endings(esp_line_endings_t mode)

Set the line endings expected to be received on UART.

This specifies the conversion between line endings received on UART and newlines ('

', LF) passed into stdin:

ESP_LINE_ENDINGS_CRLF: convert CRLF to LF
ESP_LINE_ENDINGS_CR: convert CR to LF
ESP_LINE_ENDINGS_LF: no modification

Note

this function is not thread safe w.r.t. reading from UART

Parameters: mode -- line endings expected on UART

void esp_vfs_dev_uart_set_tx_line_endings(esp_line_endings_t mode)

Set the line endings to sent to UART.

This specifies the conversion between newlines ('

', LF) on stdout and line endings sent over UART:

ESP_LINE_ENDINGS_CRLF: convert LF to CRLF
ESP_LINE_ENDINGS_CR: convert LF to CR
ESP_LINE_ENDINGS_LF: no modification

Note

this function is not thread safe w.r.t. writing to UART

Parameters: mode -- line endings to send to UART

void esp_vfs_usb_serial_jtag_use_driver(void): set VFS to use USB-SERIAL-JTAG driver for reading and writing

Note

application must configure USB-SERIAL-JTAG driver before calling these functions With these functions, read and write are blocking and interrupt-driven.

void esp_vfs_usb_serial_jtag_use_nonblocking(void): set VFS to use simple functions for reading and writing UART Read is non-blocking, write is busy waiting until TX FIFO has enough space. These functions are used by default.

Header File

components/esp_driver_uart/include/driver/uart_vfs.h
This header file can be included with:
#include "driver/uart_vfs.h"
This header file is a part of the API provided by the esp_driver_uart component. To declare that your component depends on esp_driver_uart, add the following to your CMakeLists.txt:
REQUIRES esp_driver_uart
or
PRIV_REQUIRES esp_driver_uart

Functions

void uart_vfs_dev_register(void)

Add /dev/uart virtual filesystem driver.

This function is called from startup code to enable serial output

int uart_vfs_dev_port_set_rx_line_endings(int uart_num, esp_line_endings_t mode)

Set the line endings expected to be received on specified UART.

This specifies the conversion between line endings received on UART and newlines ('

', LF) passed into stdin:

ESP_LINE_ENDINGS_CRLF: convert CRLF to LF
ESP_LINE_ENDINGS_CR: convert CR to LF
ESP_LINE_ENDINGS_LF: no modification

Note

this function is not thread safe w.r.t. reading from UART

Parameters

uart_num -- the UART number
mode -- line endings to send to UART

Returns

0 if succeeded, or -1 when an error (specified by errno) have occurred.

int uart_vfs_dev_port_set_tx_line_endings(int uart_num, esp_line_endings_t mode)

Set the line endings to sent to specified UART.

This specifies the conversion between newlines ('

', LF) on stdout and line endings sent over UART:

ESP_LINE_ENDINGS_CRLF: convert LF to CRLF
ESP_LINE_ENDINGS_CR: convert LF to CR
ESP_LINE_ENDINGS_LF: no modification

Note

this function is not thread safe w.r.t. writing to UART

Parameters

uart_num -- the UART number
mode -- line endings to send to UART

Returns

0 if succeeded, or -1 when an error (specified by errno) have occurred.

void uart_vfs_dev_use_nonblocking(int uart_num)

set VFS to use simple functions for reading and writing UART

Read is non-blocking, write is busy waiting until TX FIFO has enough space. These functions are used by default.

Parameters: uart_num -- UART peripheral number

void uart_vfs_dev_use_driver(int uart_num)

set VFS to use UART driver for reading and writing

Note

Application must configure UART driver before calling these functions With these functions, read and write are blocking and interrupt-driven.

Parameters: uart_num -- UART peripheral number

Header File

components/vfs/include/esp_vfs_eventfd.h
This header file can be included with:
#include "esp_vfs_eventfd.h"
This header file is a part of the API provided by the vfs component. To declare that your component depends on vfs, add the following to your CMakeLists.txt:
REQUIRES vfs
or
PRIV_REQUIRES vfs

Functions

esp_err_t esp_vfs_eventfd_register(const esp_vfs_eventfd_config_t *config)

Registers the event vfs.

Returns: ESP_OK if successful, ESP_ERR_NO_MEM if too many VFSes are registered.

esp_err_t esp_vfs_eventfd_unregister(void)

Unregisters the event vfs.

Returns: ESP_OK if successful, ESP_ERR_INVALID_STATE if VFS for given prefix hasn't been registered

int eventfd(unsigned int initval, int flags)

Structures

struct esp_vfs_eventfd_config_t

Eventfd vfs initialization settings.

Public Members

size_t max_fds: The maximum number of eventfds supported

Macros

EFD_SUPPORT_ISR

ESP_VFS_EVENTD_CONFIG_DEFAULT()

Header File

components/vfs/include/esp_vfs_null.h
This header file can be included with:
#include "esp_vfs_null.h"
This header file is a part of the API provided by the vfs component. To declare that your component depends on vfs, add the following to your CMakeLists.txt:
REQUIRES vfs
or
PRIV_REQUIRES vfs

Functions

const esp_vfs_t *esp_vfs_null_get_vfs(void)

Get VFS structure for /dev/null.

Returns: VFS structure for /dev/null

esp_err_t esp_vfs_null_register(void)

Register filesystem for /dev/null.

Returns: ESP_OK on success; any other value indicates an error

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Virtual Filesystem Component

Overview

FS Registration

Synchronous Input/Output Multiplexing

Non-Socket VFS Drivers

Socket VFS Drivers

Paths

File Descriptors

eventfd()

Minified VFS

Well Known VFS Devices

Application Examples

API Reference

Header File

Functions

Structures

Macros

Header File

Functions

Structures

Type Definitions

Header File

Functions

Header File

Functions

Header File

Functions

Structures

Macros

Header File

Functions

`eventfd()`