netdev - Re: [PATCH v5 bpf-next 06/10] tracepoint: compute num

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Message-ID: <20180326123530.66ced6ae@gandalf.local.home>
Date:   Mon, 26 Mar 2018 12:35:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        netdev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        linux-api <linux-api@...r.kernel.org>,
        "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [PATCH v5 bpf-next 06/10] tracepoint: compute num_args at build
 time

On Mon, 26 Mar 2018 09:25:07 -0700
Alexei Starovoitov <ast@...com> wrote:

> commit log of patch 6 states:
> 
> "for_each_tracepoint_range() api has no users inside the kernel.
> Make it more useful with ability to stop for_each() loop depending
> via callback return value.
> In such form it's used in subsequent patch."
> 
> and in patch 7:
> 
> +static void *__find_tp(struct tracepoint *tp, void *priv)
> +{
> +       char *name = priv;
> +
> +       if (!strcmp(tp->name, name))
> +               return tp;
> +       return NULL;
> +}
> ...
> +       struct tracepoint *tp;
> ...
> +       tp = for_each_kernel_tracepoint(__find_tp, tp_name);
> +       if (!tp)
> +               return -ENOENT;
> 
> still not obvious?

Please just create a new function called tracepoint_find_by_name(), and
use that. I don't see any benefit in using a for_each* function for
such a simple routine. Not to mention, you then don't need to know the
internals of a tracepoint in kernel/bpf/syscall.c.

-- Steve