File Systems

Zephyr RTOS Virtual Filesystem Switch (VFS) allows applications to mount multiple file systems at different mount points (e.g., /fatfs and /lfs). The mount point data structure contains all the necessary information required to instantiate, mount, and operate on a file system. The File system Switch decouples the applications from directly accessing an individual file system’s specific API or internal functions by introducing file system registration mechanisms.

In Zephyr, any file system implementation or library can be plugged into or pulled out through a file system registration API. Each file system implementation must have a globally unique integer identifier; use FS_TYPE_EXTERNAL_BASE to avoid clashes with in-tree identifiers.

int fs_register(int type, const struct fs_file_system_t *fs);

int fs_unregister(int type, const struct fs_file_system_t *fs);

Zephyr RTOS supports multiple instances of a file system by making use of the mount point as the disk volume name, which is used by the file system library while formatting or mounting a disk.

A file system is declared as:

static struct fs_mount_t mp = {
.type = FS_FATFS,
.mnt_point = FATFS_MNTP,
.fs_data = &fat_fs,
};

where

  • FS_FATFS is the file system type like FATFS or LittleFS.

  • FATFS_MNTP is the mount point where the file system will be mounted.

  • fat_fs is the file system data which will be used by fs_mount() API.

Samples

Samples for the VFS are mainly supplied in samples/subsys/fs, although various examples of the VFS usage are provided as important functionalities in samples for different subsystems. Here is the list of samples worth looking at:

  • samples/subsys/fs/fat_fs is an example of FAT file system usage with SDHC media;

  • samples/subsys/shell/fs is an example of Shell fs subsystem, using internal flash partition

    formatted to LittleFS;

  • samples/subsys/usb/mass/ example of USB Mass Storage device that uses FAT FS driver with RAM

    or SPI connected FLASH, or LittleFS in flash, depending on the sample configuration.

API Reference

File System APIs

Related code samples