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Date: Fri, 10 Nov 2017 12:14:29 -0500 From: Josef Bacik <josef@...icpanda.com> To: Ingo Molnar <mingo@...nel.org> Cc: Josef Bacik <josef@...icpanda.com>, rostedt@...dmis.org, mingo@...hat.com, davem@...emloft.net, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, ast@...nel.org, kernel-team@...com, daniel@...earbox.net, Josef Bacik <jbacik@...com> Subject: Re: [PATCH 1/2] bpf: add a bpf_override_function helper On Fri, Nov 10, 2017 at 10:34:59AM +0100, Ingo Molnar wrote: > > * Josef Bacik <josef@...icpanda.com> wrote: > > > @@ -551,6 +578,10 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func > > return &bpf_get_stackid_proto; > > case BPF_FUNC_perf_event_read_value: > > return &bpf_perf_event_read_value_proto; > > + case BPF_FUNC_override_return: > > + pr_warn_ratelimited("%s[%d] is installing a program with bpf_override_return helper that may cause unexpected behavior!", > > + current->comm, task_pid_nr(current)); > > + return &bpf_override_return_proto; > > So if this new functionality is used we'll always print this into the syslog? > > The warning is also a bit passive aggressive about informing the user: what > unexpected behavior can happen, what is the worst case? > It's modeled after the other warnings bpf will spit out, but with this feature you are skipping a function and instead returning some arbitrary value, so anything could go wrong if you mess something up. For instance I screwed up my initial test case and made every IO submitted return an error instead of just on the one file system I was attempting to test, so all sorts of hilarity ensued. Thanks, Josef
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