How to use configfs
Configuration file system introduction
configfs is a ram-based filesystem that provides the converse of sysfs's functionality. Where sysfs is a filesystem-based view of kernel objects, configfs is a filesystem-based manager of kernel objects, or config_items.
Both sysfs and configfs can and should exist together on the same system. One is not a replacement for the other.
Symbol: CONFIGFS_FS [=n] Prompt: Userspace-driven configuration filesystem Defined at fs/configfs/Kconfig:1 Depends on: SYSFS Location: -> Kernel configuration -> File systems -> Pseudo filesystems Selected by: NETCONSOLE_DYNAMIC && NETDEVICES && NETCONSOLE && SYSFS && EXPERIMENTAL || DLM && EXPERIMENT
PWM - example driver that uses the configuration file system
A driver is needed that uses configfs, so the Bill Gatliff PWM driver will be used as the example. If your kernel doesn't have the PWM driver, you can get it from one Bill's PWM Linux git repository.
Symbol: GPIO_PWM [=y] Prompt: GPIO+hrtimer PWM device emulation Defined at drivers/pwm/Kconfig:11 Depends on: GENERIC_PWM Location: -> Kernel configuration -> Device Drivers -> PWM Support (GENERIC_PWM [=y])
Mounting the configuration file system
First, verify your kernel has support for configfs.
fgrep configfs /proc/filesystems
with the expected output being:
Mount the configuration file system at the conventional location:
mkdir -p /config mount -t configfs none /config
Accessing the configuration file system
You can verify the PWM entries are present in the configuration file system:
with expected output:
Using PWM via the configuration file system
The PWM driver will be used as the example of how to use the configuration file system
GPIO=102 # create configurable GPIO PWM mkdir /config/gpio_pwm/$GPIO echo 1 > /sys/class/pwm/gpio_pwm\:$GPIO/export # configure for 10 ms with a 50% duty cycle - simple 100 hz square wave echo 10000000 > /sys/class/pwm/gpio_pwm\:$GPIO/period_ns echo 5000000 > /sys/class/pwm/gpio_pwm\:$GPIO/duty_ns # start the PWM echo 1 > /sys/class/pwm/gpio_pwm\:$GPIO/run # stop the PWM echo 0 > /sys/class/pwm/gpio_pwm\:$GPIO/run # destroy the configurable GPIO PWM echo 1 > /sys/class/pwm/gpio_pwm\:$GPIO/unexport rm -rf /config/gpio_pwm/$GPIO