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Module scope

This module implements an abstraction layer for POSIX-like file system APIs, to allow Pelion Device Management Client to perform file I/O operations.

Supported key functionality:

  • Folder operations: create and delete directory.
  • File operations: open, seek, read, write , close and delete (unlink).
  • Special operations:
    • Delete folder content: files only, non-recursive deletion (no folder iteration).
    • Nonrecursively copy all files in the folder to a different folder.
    • Format partition.

The pal_plat_fileSystem.h header declares the FileSystem functions.

Note: You need to implement all APIs in this module.

Prerequisites for this porting stage

  • An RTOS module (successfully ported).

  • Storage with at least one partition and a file system (on Linux, you can use gparted for partition management). One or more additional partitions may be used as backup. Note: Mbed OS supports only primary partitions. MBRBlockDevice includes a partition method that you can use for creating partitions.

  • The FileSystem module must receive at least one mount point.

  • The name of the primary and secondary mount points must be set in the PAL_FS_MOUNT_POINT_PRIMARY and PAL_FS_MOUNT_POINT_SECONDARY environment variables, respectively.

    Note: The primary and secondary mount points may be the same (for example, for single-partition systems).


The file system folder access assumes that folders are separated with the / character.


Key and Configuration Management data (KCM) files are in the ESFS folders ESFS_WORKING_DIRECTORY, in case of partition PAL_FS_MOUNT_POINT_PRIMARY, and ESFS_BACKUP_DIRECTORY, in case of partition PAL_FS_PARTITION_SECONDARY. You can override ESFS_WORKING_DIRECTORY and ESFS_BACKUP_DIRECTORY in the application configuration file. More specific details about KCM are available in Using FCC and KCM in your application.

OS-specific notes


  • You do not need a special configuration; the FileSystem functionality uses the Linux stdio.h library.
  • The default format type is ext4. If you need a different format, set PAL_PARTITION_FORMAT_TYPE (in pal_plat_filesystem.c) to the desired type.

Mbed OS

Mbed OS storage configuration.

Dual partition porting

To enable dual partition, change the value of PAL_NUMBER_OF_PARTITIONS to 2.

You must override the FileSystem::get_default_instance()method, because it is for the whole blockdevice. The PAL mount point defines PAL_FS_MOUNT_POINT_PRIMARY and PAL_FS_MOUNT_POINT_SECONDARY must match with the mount points of the filesystem instances. The default value for PAL_FS_MOUNT_POINT_PRIMARY is "/default" and "/default2" for PAL_FS_MOUNT_POINT_SECONDARY. You can override the values in the mbed_app.json file.