SPIFFS Filesystem

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Overview

SPIFFS is a file system intended for SPI NOR flash devices on embedded targets. It supports wear levelling, file system consistency checks, and more.

Notes

  • Currently, SPIFFS does not support directories, it produces a flat structure. If SPIFFS is mounted under /spiffs, then creating a file with the path /spiffs/tmp/myfile.txt will create a file called /tmp/myfile.txt in SPIFFS, instead of myfile.txt in the directory /spiffs/tmp.

  • It is not a real-time stack. One write operation might take much longer than another.

  • For now, it does not detect or handle bad blocks.

  • SPIFFS is able to reliably utilize only around 75% of assigned partition space.

  • When the filesystem is running out of space, the garbage collector is trying to find free space by scanning the filesystem multiple times, which can take up to several seconds per write function call, depending on required space. This is caused by the SPIFFS design and the issue has been reported multiple times (e.g. here) and in the official SPIFFS github repository. The issue can be partially mitigated by the SPIFFS configuration.

  • Deleting a file does not always remove the whole file, which leaves unusable sections throughout the filesystem.

  • When the chip experiences a power loss during a file system operation it could result in SPIFFS corruption. However the file system still might be recovered via esp_spiffs_check function. More details in the official SPIFFS FAQ.

Tools

spiffsgen.py

spiffsgen.py is a write-only Python SPIFFS implementation used to create filesystem images from the contents of a host folder. To use spiffsgen.py, open Terminal and run:

python spiffsgen.py <image_size> <base_dir> <output_file>

The required arguments are as follows:

  • image_size: size of the partition onto which the created SPIFFS image will be flashed.

  • base_dir: directory for which the SPIFFS image needs to be created.

  • output_file: SPIFFS image output file.

There are also other arguments that control image generation. Documentation on these arguments can be found in the tool's help:

python spiffsgen.py --help

These optional arguments correspond to a possible SPIFFS build configuration. To generate the right image, please make sure that you use the same arguments/configuration as were used to build SPIFFS. As a guide, the help output indicates the SPIFFS build configuration to which the argument corresponds. In cases when these arguments are not specified, the default values shown in the help output will be used.

When the image is created, it can be flashed using esptool.py or parttool.py.

Aside from invoking the spiffsgen.py standalone by manually running it from the command line or a script, it is also possible to invoke spiffsgen.py directly from the build system by calling spiffs_create_partition_image:

spiffs_create_partition_image(<partition> <base_dir> [FLASH_IN_PROJECT] [DEPENDS dep dep dep...])

This is more convenient as the build configuration is automatically passed to the tool, ensuring that the generated image is valid for that build. An example of this is while the image_size is required for the standalone invocation, only the partition name is required when using spiffs_create_partition_image -- the image size is automatically obtained from the project's partition table.

spiffs_create_partition_image must be called from one of the component CMakeLists.txt files.

Optionally, users can opt to have the image automatically flashed together with the app binaries, partition tables, etc. on idf.py flash by specifying FLASH_IN_PROJECT. For example:

spiffs_create_partition_image(my_spiffs_partition my_folder FLASH_IN_PROJECT)

If FLASH_IN_PROJECT/SPIFFS_IMAGE_FLASH_IN_PROJECT is not specified, the image will still be generated, but you will have to flash it manually using esptool.py, parttool.py, or a custom build system target.

There are cases where the contents of the base directory itself is generated at build time. Users can use DEPENDS/SPIFFS_IMAGE_DEPENDS to specify targets that should be executed before generating the image:

add_custom_target(dep COMMAND ...)

spiffs_create_partition_image(my_spiffs_partition my_folder DEPENDS dep)

For an example, see storage/spiffsgen.

mkspiffs

Another tool for creating SPIFFS partition images is mkspiffs. Similar to spiffsgen.py, it can be used to create an image from a given folder and then flash that image using esptool.py

For that, you need to obtain the following parameters:

  • Block Size: 4096 (standard for SPI Flash)

  • Page Size: 256 (standard for SPI Flash)

  • Image Size: Size of the partition in bytes (can be obtained from a partition table)

  • Partition Offset: Starting address of the partition (can be obtained from a partition table)

To pack a folder into a 1-Megabyte image, run:

mkspiffs -c [src_folder] -b 4096 -p 256 -s 0x100000 spiffs.bin

To flash the image onto ESP32-H2 at offset 0x110000, run:

python esptool.py --chip esp32h2 --port [port] --baud [baud] write_flash -z 0x110000 spiffs.bin

Notes on which SPIFFS tool to use

The two tools presented above offer very similar functionality. However, there are reasons to prefer one over the other, depending on the use case.

Use spiffsgen.py in the following cases:

  1. If you want to simply generate a SPIFFS image during the build. spiffsgen.py makes it very convenient by providing functions/commands from the build system itself.

  2. If the host has no C/C++ compiler available, because spiffsgen.py does not require compilation.

Use mkspiffs in the following cases:

  1. If you need to unpack SPIFFS images in addition to image generation. For now, it is not possible with spiffsgen.py.

  2. If you have an environment where a Python interpreter is not available, but a host compiler is available. Otherwise, a pre-compiled mkspiffs binary can do the job. However, there is no build system integration for mkspiffs and the user has to do the corresponding work: compiling mkspiffs during build (if a pre-compiled binary is not used), creating build rules/targets for the output files, passing proper parameters to the tool, etc.

See also

Application Example

An example of using SPIFFS is provided in the storage/spiffs directory. This example initializes and mounts a SPIFFS partition, then writes and reads data from it using POSIX and C library APIs. See the README.md file in the example directory for more information.

High-level API Reference

Header File

Functions

esp_err_t esp_vfs_spiffs_register(const esp_vfs_spiffs_conf_t *conf)

Register and mount SPIFFS to VFS with given path prefix.

Parameters

conf -- Pointer to esp_vfs_spiffs_conf_t configuration structure

Returns

  • ESP_OK if success

  • ESP_ERR_NO_MEM if objects could not be allocated

  • ESP_ERR_INVALID_STATE if already mounted or partition is encrypted

  • ESP_ERR_NOT_FOUND if partition for SPIFFS was not found

  • ESP_FAIL if mount or format fails

esp_err_t esp_vfs_spiffs_unregister(const char *partition_label)

Unregister and unmount SPIFFS from VFS

Parameters

partition_label -- Same label as passed to esp_vfs_spiffs_register.

Returns

  • ESP_OK if successful

  • ESP_ERR_INVALID_STATE already unregistered

bool esp_spiffs_mounted(const char *partition_label)

Check if SPIFFS is mounted

Parameters

partition_label -- Optional, label of the partition to check. If not specified, first partition with subtype=spiffs is used.

Returns

  • true if mounted

  • false if not mounted

esp_err_t esp_spiffs_format(const char *partition_label)

Format the SPIFFS partition

Parameters

partition_label -- Same label as passed to esp_vfs_spiffs_register.

Returns

  • ESP_OK if successful

  • ESP_FAIL on error

esp_err_t esp_spiffs_info(const char *partition_label, size_t *total_bytes, size_t *used_bytes)

Get information for SPIFFS

Parameters

  • partition_label -- Same label as passed to esp_vfs_spiffs_register

  • total_bytes -- [out] Size of the file system

  • used_bytes -- [out] Current used bytes in the file system

Returns

  • ESP_OK if success

  • ESP_ERR_INVALID_STATE if not mounted

esp_err_t esp_spiffs_check(const char *partition_label)

Check integrity of SPIFFS

Parameters

partition_label -- Same label as passed to esp_vfs_spiffs_register

Returns

  • ESP_OK if successful

  • ESP_ERR_INVALID_STATE if not mounted

  • ESP_FAIL on error

esp_err_t esp_spiffs_gc(const char *partition_label, size_t size_to_gc)

Perform garbage collection in SPIFFS partition.

Call this function to run GC and ensure that at least the given amount of space is available in the partition. This function will fail with ESP_ERR_NOT_FINISHED if it is not possible to reclaim the requested space (that is, not enough free or deleted pages in the filesystem). This function will also fail if it fails to reclaim the requested space after CONFIG_SPIFFS_GC_MAX_RUNS number of GC iterations. On one GC iteration, SPIFFS will erase one logical block (4kB). Therefore the value of CONFIG_SPIFFS_GC_MAX_RUNS should be set at least to the maximum expected size_to_gc, divided by 4096. For example, if the application expects to make room for a 1MB file and calls esp_spiffs_gc(label, 1024 * 1024), CONFIG_SPIFFS_GC_MAX_RUNS should be set to at least 256. On the other hand, increasing CONFIG_SPIFFS_GC_MAX_RUNS value increases the maximum amount of time for which any SPIFFS GC or write operation may potentially block.

Parameters

  • partition_label -- Label of the partition to be garbage-collected. The partition must be already mounted.

  • size_to_gc -- The number of bytes that the GC process should attempt to make available.

Returns

  • ESP_OK on success

  • ESP_ERR_NOT_FINISHED if GC fails to reclaim the size given by size_to_gc

  • ESP_ERR_INVALID_STATE if the partition is not mounted

  • ESP_FAIL on all other errors

Structures

struct esp_vfs_spiffs_conf_t

Configuration structure for esp_vfs_spiffs_register.

Public Members

const char *base_path

File path prefix associated with the filesystem.

const char *partition_label

Optional, label of SPIFFS partition to use. If set to NULL, first partition with subtype=spiffs will be used.

size_t max_files

Maximum files that could be open at the same time.

bool format_if_mount_failed

If true, it will format the file system if it fails to mount.

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