netdev - Re: [PATCH] net: introduce SO_BPF

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Date:	Thu, 05 Dec 2013 09:32:50 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michal Sekletár <sekletar.m@...il.com>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	Michal Sekletar <msekleta@...hat.com>, netdev@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH] net: introduce SO_BPF_EXTENSIONS

On Thu, 2013-12-05 at 18:28 +0100, Michal Sekletár wrote:
> On Fri, Nov 29, 2013 at 3:13 PM, Daniel Borkmann <dborkman@...hat.com> wrote:
> > On 11/28/2013 06:31 PM, Eric Dumazet wrote:
> >>
> >> On Thu, 2013-11-28 at 12:57 +0100, Michal Sekletar wrote:
> >>
> >>> +enum {
> >>> +       BPF_ANC_FLAG_PROTOCOL         = (1 << 0),
> >>> +       BPF_ANC_FLAG_PKTTYPE          = (1 << 1),
> >>> +       BPF_ANC_FLAG_IFINDEX          = (1 << 2),
> >>> +       BPF_ANC_FLAG_NLATTR           = (1 << 3),
> >>> +       BPF_ANC_FLAG_NLATTR_NEST      = (1 << 4),
> >>> +       BPF_ANC_FLAG_MARK             = (1 << 5),
> >>> +       BPF_ANC_FLAG_QUEUE            = (1 << 6),
> >>> +       BPF_ANC_FLAG_HATYPE           = (1 << 7),
> >>> +       BPF_ANC_FLAG_RXHASH           = (1 << 8),
> >>> +       BPF_ANC_FLAG_CPU              = (1 << 9),
> >>> +       BPF_ANC_FLAG_ALU_XOR_X        = (1 << 10),
> >>> +       BPF_ANC_FLAG_SECCOMP_LD_W     = (1 << 11),
> >>> +       BPF_ANC_FLAG_VLAN_TAG         = (1 << 12),
> >>> +       BPF_ANC_FLAG_VLAN_TAG_PRESENT = (1 << 13),
> >>> +       BPF_ANC_FLAG_PAY_OFFSET       = (1 << 14),
> >>> +};
> >>> +
> >>
> >>
> >> Why spending 15 bits (out of 32), for all these extensions ?
> >>
> >> It seems a single one should be enough.
> >>
> >> I do not think we will ever remove one of these extension.
> >
> >
> > Agreed, this will just cripple of us adding other extensions in
> > terms of uapi. I assume there won't be so much more extensions,
> > but it's of course hard to predict the future. ;-)
> >
> 
> Not sure I follow. Can you please elaborate on the explanation. Please
> bare with me this is my first kernel patch submission.

if SO_BPF_EXTENSIONS is supported, than you can assume that all current
extensions are supported.

No need to consume one bit per feature, as all these features wont ever
disappear from linux.



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