linux-kernel - Re: [PATCH v5 2/9] fprobe: Add ftrace based probe APIs

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Message-ID: <YfGVab8kNW1AkYXk@krava>
Date:   Wed, 26 Jan 2022 19:39:37 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH v5 2/9] fprobe: Add ftrace based probe APIs

On Thu, Jan 27, 2022 at 12:59:52AM +0900, Masami Hiramatsu wrote:
> On Wed, 26 Jan 2022 11:50:22 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > > one more question..
> > > 
> > > I'm adding support for user to pass function symbols to bpf fprobe link
> > > and I thought I'd pass symbols array to register_fprobe, but I'd need to
> > > copy the whole array of strings from user space first, which could take
> > > lot of memory considering attachment of 10k+ functions
> > > 
> > > so I'm thinking better way is to resolve symbols already in bpf fprobe
> > > link code and pass just addresses to register_fprobe
> > 
> > That is OK. Fprobe accepts either ::syms or ::addrs.
> > 
> > > 
> > > I assume you want to keep symbol interface, right? could we have some
> > > flag ensuring the conversion code is skipped, so we don't go through
> > > it twice?
> > 
> > Yeah, we still have many unused bits in fprobe::flags. :)
> 
> Instead of that, according to Steve's comment, I would like to introduce
> 3 registration APIs.
> 
> int register_fprobe(struct fprobe *fp, const char *filter, const char *notrace);
> int register_fprobe_ips(struct fprobe *fp, unsigned long *addrs, int num);
> int register_fprobe_syms(struct fprobe *fp, const char **syms, int num);
> 
> The register_fprobe_ips() will not touch the @addrs. You have to set the
> correct ftrace location address in the @addrs.

ok, sounds good

thanks,
jirka