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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
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