Re: [PATCH net-next 1/4] bpf: allow bpf programs to tail-call other bpf programs

On Tue, May 19, 2015 at 5:18 PM, Alexei Starovoitov [off-list ref] wrote:

On 5/19/15 5:13 PM, Andy Lutomirski wrote:

quoted

IMO this is starting to get a bit ugly.  Would it be possible to have
the program dereference the subprogram reference itself from the jump
table?  There would have to be a verifier type that represents a
reference to a program tail-call entry point, but that seems better
than having this weird indirection.

Which part? I don't think you've looked at examples yet.
network parser has to call itself. Otherwise we cannot parse 10 mpls
labels or TLVs.
Indirection via jump_table also has to be there.
We need to dynamically add and remove programs form this jump table.
It cannot be all static.

What I mean is: why do we need the interface to be "look up this index
in an array and just to what it references" as a single atomic
instruction?  Can't we break it down into first "look up this index in
an array" and then "do this tail call"?

I don't see why everything needs to be a map.

--Andy