Linux GPIOs handling

Question

I have some question about Linux kernel and GPIOs. I know that in Linux everything is file so when I do something like

echo 30 > /sys/class/gpio/export

and

echo 1 > /sys/class/gpio/gpio30/value

what really happens? I mean how does sysfs handle that? Does it call system calls implemented in gpiolib?

Answer 1

The gpiolib registers the value attribute in this way:

 static const DEVICE_ATTR(value, 0644, gpio_value_show, gpio_value_store);

It creates a device attribute named value, with permission 644; on read it calls gpio_value_show, on write it calls gpio_value_store

What sysfs does, is to redirect read and write to the correspondent function of a sysfs attribute.