linux-kernel - Re: [GIT PULL] tracing: Updates for v6.17

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Message-ID: <6z7h63sg3ljhy2k2ymnysm7hhcmtb76follkdy2y2iu54npxqj@wppxbg2qok2p>
Date: Thu, 31 Jul 2025 10:29:49 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, 
	LKML <linux-kernel@...r.kernel.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Mark Rutland <mark.rutland@....com>, Arnd Bergmann <arnd@...db.de>, Nam Cao <namcao@...utronix.de>, 
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, Yury Norov <yury.norov@...il.com>
Subject: Re: [GIT PULL] tracing: Updates for v6.17

On Thu, Jul 31, 2025 at 10:17:17AM -0400, Steven Rostedt wrote:
> 
>   When tracefs is accessed from /sys/kernel/debug/tracing, the following
>   printk is triggerd:
> 
>    pr_warn("NOTICE: Automounting of tracing to debugfs is deprecated and will be removed in 2030\n");
> 
>   This gives users another 5 years to fix their scripts.

Not objecting to PR, but I don't get the point of the warn.

In libbpf we have this logic:
#define DEBUGFS "/sys/kernel/debug/tracing"
#define TRACEFS "/sys/kernel/tracing"

static bool use_debugfs(void)
{
        static int has_debugfs = -1;

        if (has_debugfs < 0)
                has_debugfs = faccessat(AT_FDCWD, DEBUGFS, F_OK, AT_EACCESS) == 0;

        return has_debugfs == 1;
}

static const char *tracefs_path(void)
{
        return use_debugfs() ? DEBUGFS : TRACEFS;
}

So it will trigger the warn just because libbpf tries to find tracefs
in debugfs first ?
We can switch the order, no big deal.
What about other tools ?

bpftrace has similar logic:
#define DEBUGFS_TRACEFS "/sys/kernel/debug/tracing"
#define TRACEFS "/sys/kernel/tracing"

std::string path()
{
  static bool use_debugfs = access(DEBUGFS_TRACEFS, F_OK) == 0;
  return use_debugfs ? DEBUGFS_TRACEFS : TRACEFS;
}

In 5 years all these tools can switch the order, no problem,
but I don't get the point. Most, it not all tools, have similar tracefs
detection logic. Just remove automount right now without warn,
since the warn is only noise and churn to tools to swap the order
of detection ?