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

Question

For the 'tracepoint:syscalls:sys_enter_fchownat' I'm trying to print the program name and pid of the calling but also of all the parent programs.

I know pid and comm but how do I go up the tree?

I tried a number of things..

$current_pid = $pid_ns[$current_pid]->parent; parent_pid = task_struct_ptr->parent->pid;

I checked the LLMs as well but they hallucinated up a storm.

Answer 1

bpftrace questions never get any answers here :( Anyway I've been struggling towards an answer..

Tried just doing a pid/parent tree in a system() call to awk, but the calling process is long dead before awk is booted up.

Then I found that curtask->parent->pid works..

So I put that in a while loop until pid == 1 (which is basically the process top level). But then bpftrace invalidly accuses my script of having an infinite loop. So I unroll loops as a ghetto solution. Also the fact that bpftrace does not support functions... oof.

So if you read this script, it works, and it looks like jank for reasons.

#!/usr/bin/bpftrace

// touch example
// while true; do chown $RANDOM.$RANDOM example; sleep 5; done

// sys_enter_fchownat fmt: "dfd: 0x%08lx, filename: 0x%08lx, user: 0x%08lx, group: 0x%08lx, flag: 0x%08lx", ((unsigned long)(REC->dfd)), ((unsigned long)(REC->filename)), ((unsigned long)(REC->user)), ((unsigned long)(REC->group)), ((unsigned long)(REC->flag))
tracepoint:syscalls:sys_enter_fchownat
{
printf(">%llu\t%d\t%s(%s,%d,%d)", nsecs, uid, probe, str(args->filename), args->user, args->group);

$c = curtask;
$t = 0;
while($t == 0)
  {
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 1
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 2
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 3
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 4
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 5
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 6
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 7
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 8
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 9
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 10
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 11
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 12
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 13
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 14
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 15
  printf("\t...");
  $t=1;
  }

printf("\n");
}

//sys_enter_chown    fmt: "filename: 0x%08lx, user: 0x%08lx, group: 0x%08lx", ((unsigned long)(REC->filename)), ((unsigned long)(REC->user)), ((unsigned long)(REC->group))
tracepoint:syscalls:sys_enter_chown
{
printf(">%llu\t%d\t%s(%s,%d,%d)", nsecs, uid, probe, str(args->filename), args->user, args->group);

$c = curtask;
$t = 0;
while($t == 0)
  {
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 1
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 2
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 3
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 4
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 5
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 6
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 7
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 8
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 9
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 10
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 11
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 12
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 13
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 14
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 15
  printf("\t...");
  $t=1;
  }

printf("\n");
}

// sys_enter_fchown   fmt: "fd: 0x%08lx, user: 0x%08lx, group: 0x%08lx", ((unsigned long)(REC->fd)), ((unsigned long)(REC->user)), ((unsigned long)(REC->group))
tracepoint:syscalls:sys_enter_fchown
{
printf(">%llu\t%d\t%s(%d,%d)", nsecs, uid, probe, args->user, args->group);

$c = curtask;
$t = 0;
while($t == 0)
  {
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 1
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 2
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 3
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 4
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 5
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 6
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 7
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 8
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 9
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 10
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 11
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 12
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 13
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 14
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 15
  printf("\t...");
  $t=1;
  }

printf("\n");
}

// sys_enter_lchown   fmt: "filename: 0x%08lx, user: 0x%08lx, group: 0x%08lx", ((unsigned long)(REC->filename)), ((unsigned long)(REC->user)), ((unsigned long)(REC->group))
tracepoint:syscalls:sys_enter_lchown
{
printf(">%llu\t%d\t%s(%s,%d,%d))", nsecs, uid, probe, str(args->filename), args->user, args->group);

$c = curtask;
$t = 0;
while($t == 0)
  {
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 1
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 2
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 3
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 4
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 5
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 6
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 7
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 8
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 9
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 10
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 11
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 12
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 13
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 14
  if($c->pid == 1) {break;} printf("\t%s(%d)", $c->comm, $c->pid); $c = $c->parent;  // 15
  printf("\t...");
  $t=1;
  }

printf("\n");
}

// EOF