This is my bpf program to profile a kernel function pick_next_task_fiar
.
#include <uapi/linux/ptrace.h>
#include <linux/sched.h>
#include <linux/nsproxy.h>
#include <linux/pid_namespace.h>
struct rq; // forward declaration
struct val_t {
pid_t pid;
u64 vruntime;
int type; // Note, 0 for previous task, 1 for next task.
};
BPF_PERF_OUTPUT(events);
int kprobe_pick_next_fair(struct pt_regs *ctx, struct rq *rq,
struct task_struct *prev)
{
int cpu = rq->cpu;
struct val_t data = {};
data.pid = prev->pid;
data.vruntime = prev->se.vruntime;
data.type = 0;
events.perf_submit(ctx, &data, sizeof(data));
return 0;
};
It reports error as follow:
int cpu = rq->cpu;
~~^
/virtual/main.c:8:8: note: forward declaration of 'struct rq'
struct rq; // forward declaration
^
1 error generated.
Traceback (most recent call last):
File "picknextfair__back.py", line 73, in <module>
b = BPF(text=bpf_text)
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 297, in __init__
raise Exception("Failed to compile BPF text:\n%s" % text)
Exception: Failed to compile BPF text:
My question why the bpf can not recognise the struct rq
since I have already included the # include <linux/sched.h>
. However, it does recognise the struct task_struct
. These two structs are in the same head file.
Kernel version: 4.4.0-141-generic on ubuntu 16.04
struct rq
is actually not part of the kernel headers, as you can see on Bootlin.
You can either:
rq->cpu
from the rq
pointer and hardcode it in your BPF program, but I wouldn't recommend it;prev
or the current task (e.g., prev->cpu
).