Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932556AbbEUQVK (ORCPT ); Thu, 21 May 2015 12:21:10 -0400 Received: from mail-la0-f50.google.com ([209.85.215.50]:36176 "EHLO mail-la0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932499AbbEUQVI (ORCPT ); Thu, 21 May 2015 12:21:08 -0400 MIME-Version: 1.0 In-Reply-To: <555BD2E4.5050608@plumgrid.com> References: <1432079946-9878-1-git-send-email-ast@plumgrid.com> <1432079946-9878-2-git-send-email-ast@plumgrid.com> <555BD2E4.5050608@plumgrid.com> From: Andy Lutomirski Date: Thu, 21 May 2015 09:20:46 -0700 Message-ID: Subject: Re: [PATCH net-next 1/4] bpf: allow bpf programs to tail-call other bpf programs To: Alexei Starovoitov Cc: "David S. Miller" , Ingo Molnar , Daniel Borkmann , Michael Holzheu , Zi Shen Lim , Linux API , Network Development , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1302 Lines: 32 On Tue, May 19, 2015 at 5:18 PM, Alexei Starovoitov wrote: > On 5/19/15 5:13 PM, Andy Lutomirski wrote: >> >> >> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/