From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexei Starovoitov <ast@fb.com>
Subject: Re: [PATCH 1/2] bpf: add a bpf_override_function helper
Date: Wed, 1 Nov 2017 10:18:02 -0700
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Cc: Josef Bacik <jbacik@fb.com>
To: Josef Bacik <josef@toxicpanda.com>, <rostedt@goodmis.org>,
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On 11/1/17 10:00 AM, Josef Bacik wrote:
> From: Josef Bacik <jbacik@fb.com>
>
> Error injection is sloppy and very ad-hoc.  BPF could fill this niche
> perfectly with it's kprobe functionality.  We could make sure errors are
> only triggered in specific call chains that we care about with very
> specific situations.  Accomplish this with the bpf_override_funciton
> helper.  This will modify the probe'd callers return value to the
> specified value and set the PC to an override function that simply
> returns, bypassing the originally probed function.  This gives us a nice
> clean way to implement systematic error injection for all of our code
> paths.
>
> Signed-off-by: Josef Bacik <jbacik@fb.com>

Both bpf and tracing bits look great to me.
Acked-by: Alexei Starovoitov <ast@kernel.org>