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

On Wed, Jan 28, 2015 at 10:41 PM, Namhyung Kim [off-list 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.