Given this struct

struct pcap_if {
	struct pcap_if *next;
	char *name;		/* name to hand to "pcap_open_live()" */
	char *description;	/* textual description of interface, or NULL */
	struct pcap_addr *addresses;
	bpf_u_int32 flags;	/* PCAP_IF_ interface flags */
};

The code to fill the list:

pcap_if_t* find_devs()
{
   pcap_if_t *devs;
   char errbuf[PCAP_ERRBUF_SIZE];
   int res;
   res=pcap_findalldevs(&devs, errbuf);
   return devs;
 }


And the FFI code

module Pcap
  extend FFI::Library
  ffi_lib 'pcap'
  ffi_lib "#{Dir.pwd}/libpcap_ffi.so"

  attach_function :pcap_lookupdev,[:string],:string

  attach_function :find_devs,[],:pointer
  class Pcap_if_t < FFI::Struct
    layout :next,:pointer,
	   :name,:string,
	   :description,:string,
	   :pcap_addr,:pointer,
 	   :flags,:int
    def self.release ptr
      Pcap.free_object ptr
    end
  end
end

How do you iterate over the linked list using FFI?

I have tried read_array_of_pointer, it didn't seem to work.

I tried

ptr = FFI::MemoryPointer.new :pointer
ptr = Pcap.find_devs

devs = Pcap::Pcap_if_t.new ptr
puts devs[:name]

And I can get the first name, but I can't figure out how to iterate
over it.

This works but it feels wrong

while true
devs = Pcap::Pcap_if_t.new ptr
break if devs[:name].nil? or devs[:name].empty?
puts devs[:name]
ptr=devs[:next]


end


So I guess all I need is to figure out the number of elements in a
list?

******

Also is it true that FFI can not handle a multidimensional array? The
actual function to do the above has a signature of int
pcap_findalldevs(pcap_if_t **, char *); and I couldn't get it to work
without creating a C function to return pcap_if_t*.

pcap_if_t* find_devs()
{
   pcap_if_t *devs;
   char errbuf[PCAP_ERRBUF_SIZE];
   int res;
   res=pcap_findalldevs(&devs, errbuf);
   return devs;
 }