On Sun, Mar 31, 2024 at 3:34 AM Steven Rostedt rostedt@goodmis.org wrote:
On Sat, 30 Mar 2024 11:18:29 +0800 梦龙董 dongmenglong.8@bytedance.com wrote:
If you really want to have thousands of functions, why not just register it with ftrace itself. It will give you the arguments via the ftrace_regs structure. Can't you just register a program as the callback?
Ennn...I don't understand. The main purpose for me to use TRACING is:
- we can directly access the memory, which is more efficient.
I'm not sure what you mean by the above. Access what memory?
We need to use the helper of bpf_probe_read_kernel when we read "skb->sk" in kprobe, and the "skb" is the 1st arg in ip_rcv(). And we can directly read "skb->sk" in tracing, which is more efficient. Isn't it?
- we can obtain the function args in FEXIT, which kretprobe can't do it. And this is the main reason.
I didn't mention kretprobe. If you need access to the exit of the function, you can use Masami's fgraph update.
fentry -> ftrace_trampoline -> your_code
For fgraph:
fentry -> ftrace_trampoline -> fgraph [sets up return call] -> your_entry_code
function ret -> fgraph_ret_handler -> your_exit_code
And you will be able to pass data from the entry to the exit code, including parameters.
Yeah, the fgraph sounds like a nice solution to my problem. I'll have a try on it.
Thanks! Menglong Dong
-- Steve