Looking up the port(s) via /proc/ioports

The kernel provides a viewport into the port address space via the /proc/ioports pseudo-file. Let's check it out on our x86_64 guest VM (again, we're only showing part of the output):

$ sudo cat /proc/ioports 
[sudo] password for llkd: 
0000-0cf7 : PCI Bus 0000:00
  0000-001f : dma1
  0020-0021 : pic1
  0040-0043 : timer0
  0050-0053 : timer1
  0060-0060 : keyboard
  0064-0064 : keyboard
  0070-0071 : rtc_cmos
  0070-0071 : rtc0
[...]
  d270-d27f : 0000:00:0d.0
  d270-d27f : ahci
$ 

We've highlighted the keyboard ports in bold. Notice how the port numbers match what the i8042 driver code we saw previously specifies. Interestingly, running the same command on the Raspberry Pi yields nothing; this is because no driver or subsystem is using any I/O ports. Analogous with MMIO, an entry in /proc/ioports is generated when the request_region() API runs, and, conversely, is removed when the corresponding release_region...