File system usage example

Description

This basic example shows how to use a file system with RIOT in your embedded application.

In particular, this example shows:

• how to mount/format/unmount a file system, either with constfs for all devices and the default fs for devices that have a filesystem mountpoint configured by the board.
• how to open/read/write/close a file with and without newlib

A constfs file system is demonstrated with two files for all targets to demonstrate the file system functionality without an external mass storage device.

For targets that feature an onboard external mass storage device with a mount point configured, like the Nordic nRF52840 Development Kit (see boards/nrf52840dk), the flash chip is automatically added by VFS.

All the RIOT file systems are used through the vfs interface, and on most platforms files can be accessed transparently with open/close/read/write/... functions. With newlib, fopen/fclose/fread/fwrite/... can also be used transparently.

Shell commands

The following commands are available:

• vfs format /nvm0: should be called the first time only, it will format the /nvm0 mountpoint with the configured file system
• vfs mount /nvm0: mount the file system on the configured mount point The constfs file system is mounted automatically on /const when the application starts
• vfs umount /nvm0: unmount /nvm0
• cat <file>: similarly to unix cat unix command, it prints the given <file> on stdout
• tee <file> <str>: similarly to tee unix command, it writes <str> in <file>

Besides of these commands, the default vfs commands can be used, for instance:

• vfs df: shows all mountpoints and used/available file system space
• vfs ls <path>: list files

Example on native with constfs

• Build and run the filesystem example application on the native target:

make -C examples/filesystem all term
[...]
main(): This is RIOT! (Version: 2018.04-devel-/examples/filesystem)
constfs mounted successfully

• List the available files in the constfs predefined partition:

> ls /const
ls /const
/hello-world
/hello-riot
total 2 files

• Print the content of the files:

> cat /const/hello-world
cat /const/hello-world
Hello World!
> cat /const/hello-riot
cat /const/hello-riot
Hello RIOT!

Example on nrf52840dk with littlefs

• Build and flash filesystem example application of the nrf52840dk target

make BOARD=nrf52840dk -C examples/filesystem all flash
[...]

• When connecting to the board via the serial console, it should display the following output:

main(): This is RIOT! (Version: 2024.04-devel-254-gee0f6d)
constfs mounted successfully
>

• The flash chip is empty by default and has to be formatted, which can be done with the vfs format /nvm0 command. After that it has to be mounted with vfs mount /nvm0. Once the flash is formatted, it will be automatically mounted during boot.

> vfs format /nvm0
> vfs mount /nvm0
> vfs df
Mountpoint              Total         Used    Available     Use%
/const                   27 B         27 B          0 B     100%
/nvm0                   8 MiB        8 KiB     8184 KiB       0%

• After formatting, the flash is empty, but new files can be created with tee and printed with cat.

> ls /nvm0
./
../
total 0 files
>
> tee /nvm0/testfile "This is written to the flash!"
> cat /nvm0/testfile
This is written to the flash!>
> vfs ls /nvm0
./
../
testfile	30 B
total 1 files