On Mon, May 24, 2021 at 10:22 PM Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote: > > On Mon, May 24, 2021 at 12:13 PM Andrii Nakryiko > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > I second the use of BPF_PROG_TEST_RUN (a.k.a. BPF_PROG_RUN now) to > > "mirror" such APIs to user-space. We have so much BPF-side > > Except the expiration time is stored in user-space too if you just > use user-space timers to trigger BPF_PROG_TEST_RUN. > Modifying expiration based on its current value in timer callbacks > is very common. For example in conntrack use case, we want the > GC timer to run sooner in the next run if we get certain amount of > expired items in current run. I'm not entirely sure what all this means, sorry. My general point is that instead of doing bpf() syscall with a new custom command (e.g., BPF_TIMER_UPDATE), you can just fire your custom BPF program with BPF_TEST_RUN. You can pass custom timeouts or any other user-space-provided settings either through global variables, custom maps, or directly as a context. So you have full control over what should be set when and why, we just avoid adding tons of custom bpf() syscall commands for every single feature. > > > > functionality and APIs that reflecting all of that with special > > user-space-facing BPF commands is becoming quite impractical. E.g., a > > long time ago there was a proposal to add commands to push data to BPF > > ringbuf from user-space for all kinds of testing scenarios. We never > > did that because no one bothered enough, but now I'd advocate that a > > small custom BPF program that is single-shot through BPF_PROG_RUN is a > > better way to do this. Similarly for timers and whatever other > > functionality. By doing everything from BPF program we also side-step > > potential subtle differences in semantics between BPF-side and > > user-space-side. > > I am confused about what you are saying, because we can already > trigger BPF_PROG_RUN with a user-space timer for a single shot, > with the current kernel, without any modification. So this sounds like > you are against adding any timer on the eBPF side, but on the other > hand, you are secoding to Alexei's patch... I am completely lost. I'm arguing against adding more custom commands to bpf() syscall. And I was talking about triggering BPF program directly from user-space with BPF_PROG_TEST_RUN/BPF_PROG_RUN command, not through some timers. > > Very clearly, whatever you described as "single shot" is not what we > want from any perspective. I'm not sure we are even talking about the same things, so I doubt "clearly" in this case. > > Thanks.
