# Re: \[PATCH v2 linux-trace 1/8\] tracing: attach eBPF programs to tracepoints and syscalls

- List: linux-api
- 2 messages, 2 authors
- Page: https://ratatoskr.run/linux-api/2015/01/4421083/t

## Re: \[PATCH v2 linux-trace 1/8\] tracing: attach eBPF programs to tracepoints and syscalls

- From: Alexei Starovoitov \<hidden\>
- Date: 2015-01-29 07:05:16 
- Message: https://ratatoskr.run/linux-api/2015/01/4421083.md

```text
On Wed, Jan 28, 2015 at 10:41 PM, Namhyung Kim [ref] wrote:
>
> I think it's not a problem of bpf.  An user process can be killed
> anytime while it enabed events without bpf.  The only thing it should
> care is the auto-unload IMHO.

ok. I think it does indeed make sense to decouple the logic.
We can add 'auto_enable' file to achieve desired Ctrl-C behavior.
While the 'auto_enable' file is open the event will be enabled
and writes to 'enable' file will be ignored.
As soon as file closes, the event is auto-disabled.
Then user space will use 'bpf' file to attach/auto-unload
and 'auto_enable' file together.
Seem there would be a use for such 'auto_enable'
without bpf as well.

> I'm okay for not calling bpf program in NMI but not for disabling events.
>
> Suppose an user was collecting an event (including in NMI) and then
> [s]he also wanted to run a bpf program.  So [s]he wrote a program
> always return 1.  But after attaching the program, it didn't record
> the event in NMI..  Isn't that a problem?

ok, I think 'if (in_nmi()) return 1;' will work then, right?
Or you're thinking something else ?

> Right.  I think bpf programs belong to a user process but events are
> global resource.  Maybe you also need to consider attaching bpf
> program via perf (ioctl?) interface..

yes. I did. Please see my reply to Masami.
ioctl only works for tracepoints.
```

## Re: \[PATCH v2 linux-trace 1/8\] tracing: attach eBPF programs to tracepoints and syscalls

- From: Namhyung Kim \<namhyung@kernel.org\>
- Date: 2015-01-29 12:36:08 
- Message: https://ratatoskr.run/linux-api/2015/01/4421319.md

```text
On Thu, Jan 29, 2015 at 4:04 PM, Alexei Starovoitov [ref] wrote:
> On Wed, Jan 28, 2015 at 10:41 PM, Namhyung Kim [ref] wrote:
>>
>> I think it's not a problem of bpf.  An user process can be killed
>> anytime while it enabed events without bpf.  The only thing it should
>> care is the auto-unload IMHO.
>
> ok. I think it does indeed make sense to decouple the logic.
> We can add 'auto_enable' file to achieve desired Ctrl-C behavior.
> While the 'auto_enable' file is open the event will be enabled
> and writes to 'enable' file will be ignored.
> As soon as file closes, the event is auto-disabled.
> Then user space will use 'bpf' file to attach/auto-unload
> and 'auto_enable' file together.
> Seem there would be a use for such 'auto_enable'
> without bpf as well.

Why do you want such an 'auto_enable' feature?  I guess it's enough
just to keep an event in the soft-disabled state and run a bpf program
before the check.


>
>> I'm okay for not calling bpf program in NMI but not for disabling events.
>>
>> Suppose an user was collecting an event (including in NMI) and then
>> [s]he also wanted to run a bpf program.  So [s]he wrote a program
>> always return 1.  But after attaching the program, it didn't record
>> the event in NMI..  Isn't that a problem?
>
> ok, I think 'if (in_nmi()) return 1;' will work then, right?
> Or you're thinking something else ?

Nope, returning 1 would be okay..


>
>> Right.  I think bpf programs belong to a user process but events are
>> global resource.  Maybe you also need to consider attaching bpf
>> program via perf (ioctl?) interface..
>
> yes. I did. Please see my reply to Masami.
> ioctl only works for tracepoints.

What was the problem of kprobes then? :)

Thanks,
Namhyung
```