Add tracepoint example about rust-bcc

[brayniac]

Have a look at the softirqs example. https://github.com/jvns/rust-bcc/blob/master/examples/softirqs.rs

[poonai]

Hey @brayniac
I'm trying perf output with tracepoint, I'm getting the output as todo: oh no
my code :

#include <uapi/linux/ptrace.h>

BPF_PERF_OUTPUT(events);

struct kmalloc_data
{
    u32 pid;
    u64 byte_alloc;
};

int kmalloc_collector(struct tracepoint__kmem__kmalloc *args)
{
    u32 pid = bpf_get_current_pid_tgid();
    u64 alloc = args->bytes_alloc;
    struct kmalloc_data data = {};
    data.pid = pid;
    data.byte_alloc = alloc;
    events.perf_submit(args, &data, sizeof(data));
    return 0;
}

extern crate bcc;
extern crate failure;
use bcc::core::BPF;
use bcc::perf::init_perf_map;
use failure::Error;
use std::{mem, ptr, thread, time};

fn do_main() -> Result<(), Error> {
    let code = include_str!("kmalloc.c");
    let mut module = match BPF::new(code) {
        Ok(x) => x,
        Err(x) => return Err(x),
    };
    let kmalloc_collector = module.load_tracepoint("kmalloc_collector")?;
    module.attach_tracepoint("kmem", "kmalloc", kmalloc_collector)?;
    let table = module.table("events");
    let mut perfmap = init_perf_map(table, perf_callback)?;
    loop {
        perfmap.poll(200);
    }
    Ok(())
}

fn perf_callback() -> Box<FnMut(&[u8]) + Send> {
    Box::new(|x| {
        let data = parse_struct(x);
        println!("pid {} bytes allocated {}", data.pid, data.byte_alloc);
    })
}

#[repr(C)]
struct kmalloc_data {
    pid: u32,
    byte_alloc: u64,
}
fn parse_struct(x: &[u8]) -> kmalloc_data {
    unsafe { ptr::read(x.as_ptr() as *const kmalloc_data) }
}

fn main() {
    match do_main() {
        Ok(()) => println!("{}", "sup?"),
        Err(x) => eprintln!("{}", x),
    }
}

But it is working for HASH
PS: I just started rust so, my code may not be idiomatic