From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ABB9031AF17 for ; Mon, 15 Sep 2025 13:42:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757943764; cv=none; b=kAwg4U3zZO9m1QWZR5I0Xoe3Y4Boijb7tKzJttSN82IwsXxbg6Ctp3oVUA+ABFycH11tMlBuG2rdwDZB1Y+Q3QMfEELU+5Z6Pj3eYNtDyDAwPcxKnxrX6QXDWXzjaBkE+gk8zMmC+Wpa4H0tpCnxKXEh1dJxD2658WbmhxQ2XHo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757943764; c=relaxed/simple; bh=erZuEyerCGfoLXbAbs1rFxxW+uqCP4CezBqIlHGLdGM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=hjcL/LAnpmBm4Kz83D8xf7zNLsAJD+CIG8BK9oc6IBXxrGLUOMRmG5BWasYDv+k+a8uxVMOIfFW6P3n5M9pYyM5WUQRqBeVKr7CpO9r7kGNFm9sIHcNS/EYf+f6IERF97/0ijLBobqN/lFXvXiixUWGuB4pvX5rE+/V4YOxVNAQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XuTkTb4j; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XuTkTb4j" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0124FC4CEF1; Mon, 15 Sep 2025 13:42:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757943764; bh=erZuEyerCGfoLXbAbs1rFxxW+uqCP4CezBqIlHGLdGM=; h=From:To:Cc:Subject:Date:From; b=XuTkTb4je1tozHIqzmUc6KGyUG87bmKDRsnCHHyR3qVEEzulh/LkpKh6CgGrJHigJ nqPDq+jjO9PAxODpprM0AdjUhSkTyL36ZVsptrwKiBmV7Yz6/bbxIVdG3wF7gdzMWu ZhxVSfOL8V378+Z0S5Y2GvYm++T2U8uBinYvPzW44WmgeTwKUoCJtb4DaXEeXWnfzu VXtl8Vzv0AdzMYeNpkBG3FLVbUJB9GvojLAtvRYU8TJES7sZTX6eEksBrmwzEqlvgK R0MmuxSdzwlX1mhFTxNdb99itUtXu9PsEjAgg0JjavsuNk9lgqKWyzVqn8C+RM+RdJ Cd8cd/DwBJ+Yg== From: Quentin Monnet To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Steven Rostedt , bpf@vger.kernel.org, Quentin Monnet Subject: [PATCH bpf-next v2] bpftool: Search for tracefs at /sys/kernel/tracing first Date: Mon, 15 Sep 2025 14:42:09 +0100 Message-ID: <20250915134209.36568-1-qmo@kernel.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit With "bpftool prog tracelog", bpftool prints messages from the trace pipe. To do so, it first needs to find the tracefs mount point to open the pipe. Bpftool looks at a few "default" locations, including /sys/kernel/debug/tracing and /sys/kernel/tracing. Some of these locations, namely /tracing and /trace, are not standard. They are in the list because some users used to hardcode the tracing directory to short names; but we have no compelling reason to look at these locations. If we fail to find the tracefs at the default locations, we have an additional step to find it by parsing /proc/mounts anyway, so it's safe to remove these entries from the list of default locations to check. Additionally, Alexei reports that looking for the tracefs at /sys/kernel/debug/tracing may automatically mount the file system under that location, and generate a kernel log message telling that auto-mounting there is deprecated. To avoid this message, let's swap the order for checking the potential mount points: try /sys/kernel/tracing first, which should be the standard location nowadays. The kernel log message may still appear if the tracefs is not mounted on /sys/kernel/tracing when we run bpftool. Reported-by: Alexei Starovoitov Closes: https://lore.kernel.org/r/CAADnVQLcMi5YQhZKsU4z3S2uVUAGu_62C33G2Zx_ruG3uXa-Ug@mail.gmail.com/ Signed-off-by: Quentin Monnet --- v2: Remove outdated comment entirely --- tools/bpf/bpftool/tracelog.c | 11 ++--------- 1 file changed, 2 insertions(+), 9 deletions(-) diff --git a/tools/bpf/bpftool/tracelog.c b/tools/bpf/bpftool/tracelog.c index 31d806e3bdaa..573a8d99f009 100644 --- a/tools/bpf/bpftool/tracelog.c +++ b/tools/bpf/bpftool/tracelog.c @@ -57,10 +57,8 @@ find_tracefs_mnt_single(unsigned long magic, char *mnt, const char *mntpt) static bool get_tracefs_pipe(char *mnt) { static const char * const known_mnts[] = { - "/sys/kernel/debug/tracing", "/sys/kernel/tracing", - "/tracing", - "/trace", + "/sys/kernel/debug/tracing", }; const char *pipe_name = "/trace_pipe"; const char *fstype = "tracefs"; @@ -95,12 +93,7 @@ static bool get_tracefs_pipe(char *mnt) return false; p_info("could not find tracefs, attempting to mount it now"); - /* Most of the time, tracefs is automatically mounted by debugfs at - * /sys/kernel/debug/tracing when we try to access it. If we could not - * find it, it is likely that debugfs is not mounted. Let's give one - * attempt at mounting just tracefs at /sys/kernel/tracing. - */ - strcpy(mnt, known_mnts[1]); + strcpy(mnt, known_mnts[0]); if (mount_tracefs(mnt)) return false; -- 2.43.0