Jason Xing wrote:
> This patch introduces a new callback in tcp_tx_timestamp() to correlate
> tcp_sendmsg timestamp with timestamps from other tx timestamping
> callbacks (e.g., SND/SW/ACK).
>
> Without this patch, BPF program wouldn't know which timestamps belong
> to which flow because of no socket lock protection. This new callback
> is inserted in tcp_tx_timestamp() to address this issue because
> tcp_tx_timestamp() still owns the same socket lock with
> tcp_sendmsg_locked() in the meanwhile tcp_tx_timestamp() initializes
> the timestamping related fields for the skb, especially tskey. The
> tskey is the bridge to do the correlation.
>
> For TCP, BPF program hooks the beginning of tcp_sendmsg_locked() and
> then stores the sendmsg timestamp at the bpf_sk_storage, correlating
> this timestamp with its tskey that are later used in other sending
> timestamping callbacks.
>
> Signed-off-by: Jason Xing <kerneljasonxing@xxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 5 +++++
> net/ipv4/tcp.c | 4 ++++
> tools/include/uapi/linux/bpf.h | 5 +++++
> 3 files changed, 14 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 9355d617767f..86fca729fbd8 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7052,6 +7052,11 @@ enum {
> * when SK_BPF_CB_TX_TIMESTAMPING
> * feature is on.
> */
> + BPF_SOCK_OPS_TS_SND_CB, /* Called when every sendmsg syscall
> + * is triggered. It's used to correlate
> + * sendmsg timestamp with corresponding
> + * tskey.
> + */
> };
>
> /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 12b9c4f9c151..4b9739cd3bc5 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -492,6 +492,10 @@ static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
> if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK)
> shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
> }
> +
> + if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
> + SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING) && skb)
> + bpf_skops_tx_timestamping(sk, skb, BPF_SOCK_OPS_TS_SND_CB);
> }
>
> static bool tcp_stream_is_readable(struct sock *sk, int target)
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index d3e2988b3b4c..2739ee0154a0 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -7042,6 +7042,11 @@ enum {
> * when SK_BPF_CB_TX_TIMESTAMPING
> * feature is on.
> */
> + BPF_SOCK_OPS_TS_SND_CB, /* Called when every sendmsg syscall
> + * is triggered. It's used to correlate
> + * sendmsg timestamp with corresponding
> + * tskey.
> + */
Feel free to decline this late in the review process, but a bit more
bikeshedding..
Can we spell out TSTAMP instead of TS in these definitions? Within
the context of this series it is self-explanatory, but when reading
kernel code the meaning of a two letter acronym is not that clear.
And instead of SND can we use SENDMSG or something like that?
SND here confused me as the software timestamp is SCM_TSTAMP_SND.
For instance:
BPF_SOCK_OPS_TSTAMP_SENDMSG_CB,
BPF_SOCK_OPS_TSTAMP_SCHED_CB,
BPF_SOCK_OPS_TSTAMP_SND_SW_CB,
BPF_SOCK_OPS_TSTAMP_SND_HW_CB,
(BPF_SOCK_OPS_TSTAMP_TX_COMPLETION_CB,)
BPF_SOCK_OPS_TSTAMP_ACK_CB,
(not sure what the OPT in OPT_CB added).
