On Tue, Jul 16, 2019 at 06:31:17PM -0400, Steven Rostedt wrote:
On Tue, 16 Jul 2019 17:30:50 -0400 Joel Fernandes joel@joelfernandes.org wrote:
I don't see why a new bpf node for a trace event is a bad idea, really. tracefs is how we deal with trace events on Android. We do it in production systems. This is a natural extension to that and fits with the security model well.
What I would like to see is a way to have BPF inject data into the ftrace ring buffer directly. There's a bpf_trace_printk() that I find a bit of a hack (especially since it hooks into trace_printk() which is only for debugging purposes). Have a dedicated bpf ftrace ring buffer event that can be triggered is what I am looking for. Then comes the issue of what ring buffer to place it in, as ftrace can have multiple ring buffer instances. But these instances are defined by the tracefs instances directory. Having a way to associate a bpf program to a specific event in a specific tracefs directory could allow for ways to trigger writing into the correct ftrace buffer.
But his problem is with doing the association of a BPF program with tracefs itself. How would you attach a BPF program with tracefs without doing a text based approach? His problem is with the text based approach per his last email.
But looking over the patches, I see what Alexei means that there's no overlap with ftrace and these patches except for the tracefs directory itself (which is part of the ftrace infrastructure). And the trace events are technically part of the ftrace infrastructure too. I see the tracefs interface being used, but I don't see how the bpf programs being added affect the ftrace ring buffer or other parts of ftrace. And I'm guessing that's what is confusing Alexei.
In a follow-up patch which I am still writing, I am using the trace ring buffer as temporary storage since I am formatting the trace event into it. This patch you are replying to is just for raw tracepoint and yes, I agree this one does not use the ring buffer, but a future addition to it does. So I don't think the association of this patch series with ftrace is going to be an issue IMO.
thanks,
- Joel