Linux/PROCESSOR-SDK-AM335X: initialization of SYSFS / export GPIO

Tool/software: Linux

I can export gpio by using the echo shell command: echo <gipo num> > /sys/class/gpio/export  .

I'm using the prebuild file system of the SDK and I would like to know to how do the same when linux is started.

Is it done by init script? if so, which script in the SDK file system?

Thanks