Re: [PATCH bpf-next v6 05/11] bpf: Adds field bpf_sock_ops_cb_flags to tcp_sock
From: Alexei Starovoitov <hidden>
Date: 2018-01-20 03:52:25
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 <ast@kernel.org> Eric, does this approach address your concerns?