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

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Message-ID: <555BD2E4.5050608@plumgrid.com>
Date:	Tue, 19 May 2015 17:18:44 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Zi Shen Lim <zlim.lnx@...il.com>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 1/4] bpf: allow bpf programs to tail-call other
 bpf programs

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.

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