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FileSystem

The file system API provides a common interface for implementing a file system on a block-based storage device. The file system API is a class-based interface, but implementing the file system API provides the standard POSIX file API familiar to C users.

The main purpose of a FileSystem is to be instantiated. The FileSystem's constructor can take in a BlockDevice and mount point specified as a string, as well as other implementation-specific configuration options. The mount point can then act as the first directory in any paths in Mbed OS when used with the POSIX API. This gives you access to files inside the file system. The mount point can be NULL if you only need to use the FileSystem as a C++ object.

The FileSystem's file and dir functions are protected because you should not use the FileSystem file and dir functions directly. They are only a convenience for implementors. Instead, the File and Dir classes provide access to file and directory operations in a C++ class that respects RAII and other C++ conventions.

File system class reference

Public Member Functions
 FileSystem (const char *name=NULL)
virtual int mount (BlockDevice *bd)=0
virtual int unmount ()=0
virtual int reformat (BlockDevice *bd=NULL)
virtual int remove (const char *path)
virtual int rename (const char *path, const char *newpath)
virtual int stat (const char *path, struct stat *st)
virtual int mkdir (const char *path, mode_t mode)
virtual int statvfs (const char *path, struct statvfs *buf)
 Public Member Functions inherited from mbed::FileSystemLike
 FileSystemLike (const char *name=NULL)
FileHandleopen (const char *path, int flags)
DirHandleopendir (const char *path)
 Public Member Functions inherited from mbed::FileSystemHandle
virtual ~FileSystemHandle ()
 Public Member Functions inherited from mbed::FileBase
 FileBase (const char *name, PathType t)
const char * getName (void)
PathType getPathType (void)
Protected Member Functions
virtual int file_open (fs_file_t *file, const char *path, int flags)=0
virtual int file_close (fs_file_t file)=0
virtual ssize_t file_read (fs_file_t file, void *buffer, size_t size)=0
virtual ssize_t file_write (fs_file_t file, const void *buffer, size_t size)=0
virtual int file_sync (fs_file_t file)
virtual int file_isatty (fs_file_t file)
virtual off_t file_seek (fs_file_t file, off_t offset, int whence)=0
virtual off_t file_tell (fs_file_t file)
virtual void file_rewind (fs_file_t file)
virtual off_t file_size (fs_file_t file)
virtual int dir_open (fs_dir_t *dir, const char *path)
virtual int dir_close (fs_dir_t dir)
virtual ssize_t dir_read (fs_dir_t dir, struct dirent *ent)
virtual void dir_seek (fs_dir_t dir, off_t offset)
virtual off_t dir_tell (fs_dir_t dir)
virtual void dir_rewind (fs_dir_t dir)
virtual size_t dir_size (fs_dir_t dir)
virtual int open (FileHandle **file, const char *path, int flags)
virtual int open (DirHandle **dir, const char *path)
Friends
class File
class Dir
Additional Inherited Members
 Static Public Member Functions inherited from mbed::FileBase
static FileBaselookup (const char *name, unsigned int len)
static FileBaseget (int n)

File system example

/* mbed Microcontroller Library
 * Copyright (c) 2006-2013 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include "mbed.h"
#include <stdio.h>
#include <errno.h>

// Block devices
#include "SPIFBlockDevice.h"
#include "DataFlashBlockDevice.h"
#include "SDBlockDevice.h"
#include "HeapBlockDevice.h"

// File systems
#include "LittleFileSystem.h"
#include "FATFileSystem.h"


// Physical block device, can be any device that supports the BlockDevice API
SPIFBlockDevice bd(
        MBED_CONF_SPIF_DRIVER_SPI_MOSI,
        MBED_CONF_SPIF_DRIVER_SPI_MISO,
        MBED_CONF_SPIF_DRIVER_SPI_CLK,
        MBED_CONF_SPIF_DRIVER_SPI_CS);

// File system declaration
LittleFileSystem fs("fs");


// Set up the button to trigger an erase
InterruptIn irq(BUTTON1);
void erase() {
    printf("Initializing the block device... ");
    fflush(stdout);
    int err = bd.init();
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        error("error: %s (%d)\n", strerror(-err), err);
    }

    printf("Erasing the block device... ");
    fflush(stdout);
    err = bd.erase(0, bd.size());
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        error("error: %s (%d)\n", strerror(-err), err);
    }

    printf("Deinitializing the block device... ");
    fflush(stdout);
    err = bd.deinit();
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        error("error: %s (%d)\n", strerror(-err), err);
    }
}


// Entry point for the example
int main() {
    printf("--- Mbed OS filesystem example ---\n");

    // Setup the erase event on button press, use the event queue
    // to avoid running in interrupt context
    irq.fall(mbed_event_queue()->event(erase));

    // Try to mount the filesystem
    printf("Mounting the filesystem... ");
    fflush(stdout);
    int err = fs.mount(&bd);
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        // Reformat if we can't mount the filesystem
        // this should only happen on the first boot
        printf("No filesystem found, formatting... ");
        fflush(stdout);
        err = fs.reformat(&bd);
        printf("%s\n", (err ? "Fail :(" : "OK"));
        if (err) {
            error("error: %s (%d)\n", strerror(-err), err);
        }
    }

    // Open the numbers file
    printf("Opening \"/fs/numbers.txt\"... ");
    fflush(stdout);
    FILE *f = fopen("/fs/numbers.txt", "r+");
    printf("%s\n", (!f ? "Fail :(" : "OK"));
    if (!f) {
        // Create the numbers file if it doesn't exist
        printf("No file found, creating a new file... ");
        fflush(stdout);
        f = fopen("/fs/numbers.txt", "w+");
        printf("%s\n", (!f ? "Fail :(" : "OK"));
        if (!f) {
            error("error: %s (%d)\n", strerror(errno), -errno);
        }

        for (int i = 0; i < 10; i++) {
            printf("\rWriting numbers (%d/%d)... ", i, 10);
            fflush(stdout);
            err = fprintf(f, "    %d\n", i);
            if (err < 0) {
                printf("Fail :(\n");
                error("error: %s (%d)\n", strerror(errno), -errno);
            }
        }
        printf("\rWriting numbers (%d/%d)... OK\n", 10, 10);

        printf("Seeking file... ");
        fflush(stdout);
        err = fseek(f, 0, SEEK_SET);
        printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
        if (err < 0) {
            error("error: %s (%d)\n", strerror(errno), -errno);
        }
    }

    // Go through and increment the numbers
    for (int i = 0; i < 10; i++) {
        printf("\rIncrementing numbers (%d/%d)... ", i, 10);
        fflush(stdout);

        // Get current stream position
        long pos = ftell(f);

        // Parse out the number and increment
        int32_t number;
        fscanf(f, "%d", &number);
        number += 1;

        // Seek to beginning of number
        fseek(f, pos, SEEK_SET);
    
        // Store number
        fprintf(f, "    %d\n", number);

        // Flush between write and read on same file
        fflush(f);
    }
    printf("\rIncrementing numbers (%d/%d)... OK\n", 10, 10);

    // Close the file which also flushes any cached writes
    printf("Closing \"/fs/numbers.txt\"... ");
    fflush(stdout);
    err = fclose(f);
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }
    
    // Display the root directory
    printf("Opening the root directory... ");
    fflush(stdout);
    DIR *d = opendir("/fs/");
    printf("%s\n", (!d ? "Fail :(" : "OK"));
    if (!d) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    printf("root directory:\n");
    while (true) {
        struct dirent *e = readdir(d);
        if (!e) {
            break;
        }

        printf("    %s\n", e->d_name);
    }

    printf("Closing the root directory... ");
    fflush(stdout);
    err = closedir(d);
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    // Display the numbers file
    printf("Opening \"/fs/numbers.txt\"... ");
    fflush(stdout);
    f = fopen("/fs/numbers.txt", "r");
    printf("%s\n", (!f ? "Fail :(" : "OK"));
    if (!f) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    printf("numbers:\n");
    while (!feof(f)) {
        int c = fgetc(f);
        printf("%c", c);
    }

    printf("\rClosing \"/fs/numbers.txt\"... ");
    fflush(stdout);
    err = fclose(f);
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    // Tidy up
    printf("Unmounting... ");
    fflush(stdout);
    err = fs.unmount();
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(-err), err);
    }
        
    printf("Mbed OS filesystem example done!\n");
}


Sector requirements

LittleFS requirements:

  • 4 blocks root dir.
  • 2 blocks per dir.
  • 1 block per file.

FATFS requirements:

  • Hard minimum: 256 blocks.
  • 128 blocks for FAT table.
  • 1 block per dir.
  • 1 block per file.
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