netdev - Re: [PATCHv2 bpf 1/2] bpf: Support sk lookup in netns with id 0

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Date:   Fri, 30 Nov 2018 15:27:27 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Joe Stringer <joe@...d.net.nz>
Cc:     daniel@...earbox.net, ast@...nel.org,
        netdev <netdev@...r.kernel.org>, David Ahern <dsahern@...il.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: Re: [PATCHv2 bpf 1/2] bpf: Support sk lookup in netns with id 0

On Fri, Nov 30, 2018 at 03:18:25PM -0800, Joe Stringer wrote:
> On Fri, 30 Nov 2018 at 14:42, Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Thu, Nov 29, 2018 at 04:29:33PM -0800, Joe Stringer wrote:
> > > David Ahern and Nicolas Dichtel report that the handling of the netns id
> > > 0 is incorrect for the BPF socket lookup helpers: rather than finding
> > > the netns with id 0, it is resolving to the current netns. This renders
> > > the netns_id 0 inaccessible.
> > >
> > > To fix this, adjust the API for the netns to treat all negative s32
> > > values as a lookup in the current netns, while any values with a
> > > positive value in the signed 32-bit integer space would result in a
> > > lookup for a socket in the netns corresponding to that id. As before, if
> > > the netns with that ID does not exist, no socket will be found.
> > > Furthermore, if any bits are set in the upper 32-bits, then no socket
> > > will be found.
> > >
> > > Signed-off-by: Joe Stringer <joe@...d.net.nz>
> > ..
> > > +/* Current network namespace */
> > > +#define BPF_CURRENT_NETNS            (-1L)
> >
> > I was about to apply it, but then noticed that the name doesn't match
> > the rest of the names.
> > Could you rename it to BPF_F_CURRENT_NETNS ?
> 
> I skipped the F_ part since it's not really a flag, it's a value. I
> can put it back though.

BPF_F_ prefix has smaller chance of conflicts.
I wish we did that sooner.
In retrospect BPF_ANY, BPF_EXIST were poorly picked names.