On Thu, Dec 30, 2021 at 10:12 AM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Wed, Dec 29, 2021 at 6:07 PM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote: > > > > On Thu, Dec 30, 2021 at 12:46 AM Alexei Starovoitov > > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > > On Wed, Dec 29, 2021 at 3:33 AM <menglong8.dong@xxxxxxxxx> wrote: > > > > > > > > From: Menglong Dong <imagedong@xxxxxxxxxxx> > > > > > > > > The cgroup eBPF attach type 'CGROUP_SOCK_OPS' is able to monitor the > > > > state change of a tcp connect with 'BPF_SOCK_OPS_STATE_CB' ops. > > > > > > > > However, it can't trace the whole state change of a tcp connect. While > > > > a connect becomes 'TCP_TIME_WAIT' state, this sock will be release and > > > > a tw sock will be created. While tcp sock release, 'TCP_CLOSE' state > > > > change will be passed to eBPF program. Howeven, the real state of this > > > > connect is 'TCP_TIME_WAIT'. > > > > > > > > To make eBPF get the real state change of a tcp connect, add > > > > 'CGROUP_TWSK_CLOSE' cgroup attach type, which will be called when > > > > tw sock release and tcp connect become CLOSE. > > > > > > The use case is not explained. > > > > Sorry for the absence of use cases and selftests. In my case, it is for NAT of > > a docker container. > > > > Simply speaking, I'll add an element to a hash map during sys_connect() with > > 'BPF_SOCK_OPS_TCP_CONNECT_CB' ops of 'BPF_CGROUP_SOCK_OPS' > > cgroup attach type. Therefore, the received packet of the host can do DNAT > > according to the hash map. > > > > I need to release the element in the hashmap when the connection closes. > > With the help of 'BPF_SOCK_OPS_STATE_CB', I can monitor the TCP_CLOSE > > of the connection. However, as I mentioned above, it doesn't work well when > > it comes to tw sock. When the connect become 'FIN_WAIT2' or 'TIME_WAIT', > > the state of the tcp sock becomes 'TCP_CLOSE', which doesn't match the connect > > state. Therefore, the 'fin' packet that the host received can't be DNAT, as the > > element is already removed. > > > > In this patch, BPF_SOCK_OPS_TW_CLOSE_FLAG is introduced, which is used > > make 'BPF_SOCK_OPS_STATE_CB' not called when this sock becomes > > TCP_CLOSE if it is being replaced with a tw sock. > > > > > Why bpf tracing cannot be used to achieve the same? > > > > En...do you mean kprobe based eBPF trace? It can work, but I don't think it's > > high-performance, especially for network NAT. Strictly speaking, attach types, > > such as 'CGROUP_INET_SOCK_RELEASE', can be replaced by bpf tracing, but > > they exist out of performance. > > kprobe at the entry is pretty fast. > fentry is even faster. It's actually faster than cgroup based hook. Really? Doesn't it already consider the data copy of bpf_probe_read()? After all, sock based eBPF can read sock data directly. What's more, I'm not sure bpf tracing is enough, because I do NAT not for all the docker containers, which means not all tcp connect close should call my eBPF program, and that's the advantage of cgroup based eBPF. Thanks! Menglong Dong > Give it a shot.
