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?