On Fri, 2018-01-19 at 19:52 -0800, Alexei Starovoitov wrote:
> On Fri, Jan 19, 2018 at 05:45:42PM -0800, Lawrence Brakmo wrote:
> > Adds field bpf_sock_ops_cb_flags to tcp_sock and bpf_sock_ops. Its primary
> > use is to determine if there should be calls to sock_ops bpf program at
> > various points in the TCP code. The field is initialized to zero,
> > disabling the calls. A sock_ops BPF program can set it, per connection and
> > as necessary, when the connection is established.
> >
> > It also adds support for reading and writting the field within a
> > sock_ops BPF program. Reading is done by accessing the field directly.
> > However, writing is done through the helper function
> > bpf_sock_ops_cb_flags_set, in order to return an error if a BPF program
> > is trying to set a callback that is not supported in the current kernel
> > (i.e. running an older kernel). The helper function returns 0 if it was
> > able to set all of the bits set in the argument, a positive number
> > containing the bits that could not be set, or -EINVAL if the socket is
> > not a full TCP socket.
>
> ...
> > +/* Sock_ops bpf program related variables */
> > +#ifdef CONFIG_BPF
> > + u8 bpf_sock_ops_cb_flags; /* Control calling BPF programs
> > + * values defined in uapi/linux/tcp.h
>
> I guess we can extend u8 into u16 or more if necessary in the future.
>
> > + * int bpf_sock_ops_cb_flags_set(bpf_sock_ops, flags)
> > + * Set callback flags for sock_ops
> > + * @bpf_sock_ops: pointer to bpf_sock_ops_kern struct
> > + * @flags: flags value
> > + * Return: 0 for no error
> > + * -EINVAL if there is no full tcp socket
> > + * bits in flags that are not supported by current kernel
>
> ...
> > +BPF_CALL_2(bpf_sock_ops_cb_flags_set, struct bpf_sock_ops_kern *, bpf_sock,
> > + int, argval)
> > +{
> > + struct sock *sk = bpf_sock->sk;
> > + int val = argval & BPF_SOCK_OPS_ALL_CB_FLAGS;
> > +
> > + if (!sk_fullsock(sk))
> > + return -EINVAL;
> > +
> > +#ifdef CONFIG_INET
> > + if (val)
> > + tcp_sk(sk)->bpf_sock_ops_cb_flags = val;
> > +
> > + return argval & (~BPF_SOCK_OPS_ALL_CB_FLAGS);
>
> interesting idea! took me some time to realize the potential
> of such semantics, but now I like it a lot.
> It blends 'set good flag' with 'which flags are supported' logic
> into single helper. Nice.
> Thanks for adding a test for both ways.
> Acked-by: Alexei Starovoitov <a...@kernel.org>
>
> Eric, does this approach address your concerns?
Yes, this seems fine, thanks.
