receive UDP on a very wide range of multiple ports
 

i have a use for a way for a program to receive datagrams (UDP) on a very wide range of ports, wider than the number of file descriptors a single process could have open. i am wondering if there is some way to bind a single socket to receive datagrams over a specified range of ports, or every port. the process can be initialized with root permissions.

You can add a hook on netfilter. If incoming packet meet condition, it is inserted into a FIFO. In user space, a socket program read the FIFO and process it.

how is the condition expressed? would it be possible to just send ALL UDP to one process (one condition, that it is UDP)?

Netfilter handles all incoming packet no matter UDP or TCP.

but ... how do you express a netfilter rule to send all UDP packets destined for ports 4000..7999 on this host to be sent to the process running program "foo" or a named socket "foo" or a named fifo "foo"? do you have examples?

Netfilter doesn't like iptable, iptable has rule concept. Netfilter is C code hook.
Here is example, http://heapspray.net/post/writing-a-...r-3xx-kernels/

the rules get put in place in the kernel. i am talking about the rule form itself. that would be how the iptables command communicates with the kernel. but for discussion i am only talking about rules conceptually since the real goal is something else. so the input to iptables or the output (to the kernel) from iptables is what i am wanting to know.

Iptable should have some limitation because it is command line. But netfilter is C code hook, no limitation.