linux-kernel - Re: [RFC PATCH -tip 0/5] kprobes: Abolish jprobe APIs

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Message-ID: <20171007085500.r7d2hscgotxjyfkg@gmail.com>
Date:   Sat, 7 Oct 2017 10:55:00 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Ian McDonald <ian.mcdonald@...di.co.nz>,
        Vlad Yasevich <vyasevich@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [RFC PATCH -tip 0/5] kprobes: Abolish jprobe APIs


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 6 Oct 2017 13:49:59 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > Steve, could you write a documentation how to use ftrace callback?
> > I think I should update the Documentation/kprobes.txt so that jprobe
> > user can easily migrate on that.
> 
> I decided to do this now. Here's a first draft. What do you think?
> 
> -- Steve
> 
> 		Using ftrace to hook to functions
> 		=================================
> 
> Copyright 2017 VMware Inc.
>    Author:   Steven Rostedt <srostedt@...dmis.org>
>   License:   The GNU Free Documentation License, Version 1.2
>                (dual licensed under the GPL v2)
> 
> Written for: 4.14
> 
> Introduction
> ------------
> 
> The ftrace infrastructure was originially created to attach hooks to the
> beginning of functions in order to record and trace the flow of the kernel.
> But hooks to the start of a function can have other use cases. Either
> for live kernel patching, or for security monitoring. This document describes
> how to use ftrace to implement your own function hooks.
> 
> 
> The ftrace context
> ==================
> 
> WARNING: The ability to add a callback to almost any function within the
> kernel comes with risks. A callback can be called from any context
> (normal, softirq, irq, and NMI). Callbacks can also be called just before
> going to idle, during CPU bring up and takedown, or going to user space.
> This requires extra care to what can be done inside a callback. A callback
> can be called outside the protective scope of RCU.
> 
> The ftrace infrastructure has some protections agains recursions and RCU
> but one must still be very careful how they use the callbacks.
> 
> 
> The ftrace_ops structure
> ========================
> 
> To register a function callback, a ftrace_ops is required. This structure
> is used to tell ftrace what function should be called as the callback
> as well as what protections the callback will perform and not require
> ftrace to handle.

So the text first starts talking about 'hooks' then uses the 'callback' 
terminology in the rest of th document. Could we please change it all to 
'callback'?

[ This is a pet peeve of mine as 'hook' gives me the cringe! ;-) ]

Thanks,

	Ingo