bpftrace – How do I print a tree of parents for the calling process?

Have you ever wondered how to print a tree of parents for the calling process using bpftrace? Look no further! In this article, we’ll dive into the world of bpftrace and explore the ways to achieve this feat. But before we begin, let’s take a step back and understand what bpftrace is and why it’s an essential tool for system debugging and observability.

What is bpftrace?

bpftrace is a high-level tracing language that allows you to write efficient and safe tracing programs. It’s built on top of the Linux kernel’s eBPF (extended Berkeley Packet Filter) technology, which provides a sandboxed environment for executing bpftrace programs. bpftrace allows you to write programs that can attach to various kernel events, such as system calls, network events, and more, and extract valuable information from them.

Why use bpftrace?

bpftrace is an excellent tool for system debugging and observability because of its:

• Low overhead: bpftrace programs have a minimal impact on system performance.
• Safety: bpftrace runs in a sandboxed environment, ensuring that even if a program crashes, it won’t bring down the entire system.
• Flexibility: bpftrace allows you to write custom programs that can attach to various kernel events and extract specific information.
• High-level language: bpftrace has a simple and intuitive syntax, making it easy to write tracing programs.

Printing a tree of parents for the calling process

Now that we’ve covered the basics of bpftrace, let’s dive into the main topic: printing a tree of parents for the calling process. To achieve this, we’ll use bpftrace’s built-in `pid` and `ppid` fields, which represent the current process ID and parent process ID, respectively.

Using the `ppid` field

The simplest way to print the parent process ID is by using the `ppid` field. Here’s an example program:

tracepoint:syscalls:sys_enter_execve
{
  printf("%d %d\n", pid, ppid);
}

This program attaches to the `sys_enter_execve` tracepoint, which is triggered whenever a process calls the `execve` system call. The `printf` statement prints the current process ID (`pid`) and parent process ID (`ppid`) to the console.

Recursively printing parent processes

While the previous program prints the parent process ID, it doesn’t provide a tree-like structure showing the hierarchy of parent processes. To achieve this, we can use a recursive function that calls itself with the parent process ID as an argument.

func print_parents(pid_t pid)
{
  printf("%d ", pid);
  if (pid != 0) {
    print_parents(ppid);
  }
}

tracepoint:syscalls:sys_enter_execve
{
  print_parents(pid);
  printf("\n");
}

This program defines a `print_parents` function that takes a process ID as an argument. The function prints the process ID and then calls itself with the parent process ID (`ppid`) as an argument, recursively printing the parent process IDs until it reaches the root process (PID 0). The `tracepoint` attaches to the same `sys_enter_execve` event as before, and the `print_parents` function is called with the current process ID (`pid`) as an argument.

Printing a tree of parents

To print a tree-like structure showing the hierarchy of parent processes, we can modify the previous program to use indentation to represent the parent-child relationships.

func print_parents(pid_t pid, int indent)
{
  for (i = 0; i < indent; i++) {
    printf("  ");
  }
  printf("%d\n", pid);
  if (pid != 0) {
    print_parents(ppid, indent + 1);
  }
}

tracepoint:syscalls:sys_enter_execve
{
  print_parents(pid, 0);
}

This program defines the same `print_parents` function as before, but with an additional `indent` parameter. The function prints the process ID with the specified indentation level, and then calls itself with the parent process ID and increased indentation level. The `tracepoint` attaches to the same `sys_enter_execve` event as before, and the `print_parents` function is called with the current process ID (`pid`) and an initial indentation level of 0.

Conclusion

In this article, we’ve explored the world of bpftrace and learned how to print a tree of parents for the calling process. We’ve covered the basics of bpftrace, including its advantages and uses, and then dived into the specifics of printing parent process IDs and recursively printing parent processes. Finally, we modified the program to print a tree-like structure showing the hierarchy of parent processes.

bpftrace is a powerful tool for system debugging and observability, and with its high-level language and flexibility, it’s an essential tool for anyone working with Linux systems.

Additional resources

For more information on bpftrace, check out the following resources:

• bpftrace GitHub repository
• bpftrace manual page
• bpftrace tutorial by Brendan Gregg

With bpftrace, the possibilities are endless, and we hope this article has sparked your interest in exploring the world of tracing and system observability.

Frequently Asked Question

Get ready to master the art of tracing process parents with bpftrace!