Thank you, that provides a welcome solution. The Fedora case is
slightly different:
[ryniker@RPi3-1 ~]$ ls /sys/class/gpio
export gpiochip970 unexport
[ryniker@RPi3-1 ~]$ cat /sys/class/gpio/gpiochip970/base
970
Now the following works (at least there is no complaint; I will run a
real application later to check actual output, but expect no trouble):
[root@RPi3-1 ryniker]# echo 993 >/sys/class/gpio/export
[ryniker@RPi3-1 ~]$ ls /sys/class/gpio/gpio993
active_low device direction edge power subsystem uevent value
[root@RPi3-1 ryniker]# echo 993 >/sys/class/gpio/unexport
I wonder how stable the "970" is. Will it be the same for all Raspberry
Pi models? Will it be the same for all Fedora builds to run on a
specific hardware model? I suspect the safe answer is "No." Even if
this has been true for previous cases, without some explicit design
assurance it may change in the future.
Next question: how do I get /dev/i2c and /dev/spi in Fedora when there is
no /boot/config.txt file?