Setting BPF_SPECIAL_VLAN_HANDLING on a "dead" handle

[Bill Fenner <fenner () gmail com>]

Hi all,

I have a little program that basically
calls pcap_open_dead(), pcap_compile(), and then dumps the instructions
like a C struct, so that we can include a bpf program in some other code
that will use it later.  (Like "tcpdump -dd", but with a little extra
formatting.)

We may know that we will be using this code on a kernel that
requires BPF_SPECIAL_VLAN_HANDLING, and so I'd like to be able to set that
flag on a "dead" handle.  Obviously, the current mechanism is to test this
dynamically when the handle is live.

Does anyone have any opinions about how to implement this, through the
generic pcap interface?  I can think of two possibilities:

1. implement set_special_vlan_handling_op, and have it implemented by dead
and linux, and have the default version return an error
2. implement set_bpf_codegen_flags_op, and have a generic implementation,
assuming that the caller completely knows what they are doing. Then move
the definition of BPF_SPECIAL_VLAN_HANDLING from pcap-int.h to the public
header.

Anyone have a preference of which one I should go with, and/or have a
better suggestion?

Thanks,
  Bill
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