Re: [PATCH bpf-next v4 0/7] Introduce BPF_MODIFY_RET tracing progs

On 04-Mar 14:17, Alexei Starovoitov wrote:

On Wed, Mar 04, 2020 at 08:18:46PM +0100, KP Singh wrote:

quoted

Here is an example of how a fmod_ret program behaves:

int func_to_be_attached(int a, int b)

V> {  <--- do_fentry

quoted

do_fmod_ret:
   <update ret by calling fmod_ret>
   if (ret != 0)
        goto do_fexit;

original_function:

    <side_effects_happen_here>

}  <--- do_fexit

ALLOW_ERROR_INJECTION(func_to_be_attached, ERRNO)

The fmod_ret program attached to this function can be defined as:

SEC("fmod_ret/func_to_be_attached")
int BPF_PROG(func_name, int a, int b, int ret)
{
        // This will skip the original function logic.
        return -1;
}

Applied to bpf-next. Thanks.

Thanks.

I think it sets up a great base to parallelize further work.

Totally Agreed!

1. I'm rebasing my sleepable BPF patches on top.
It's necessary to read enviroment variables without the
'opportunistic copy before hand' hack I saw in your github tree

:) Sleepable BPF would indeed make it much simpler.

to do bpf_get_env_var() helper.

2. please continue on LSM_HOOK patches to go via security tree.

3. we need a volunteer to generalize bpf_sk_storage to task and inode structs.

This is quite important, especially for some of the examples we had
brought up.

I can take a look at the generalization of bpf_sk_storage.

Thanks!
- KP

This work will be super useful for all bpf tracing too.
Sleepable progs are useful for tracing as well.