From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (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 B96571096F; Fri, 17 Jan 2025 02:20:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737080458; cv=none; b=sU6dTauo8qyRSqeC6WZKqqPPawaVmodSVojFFVjpN9G7vyz/yrMKhJ7K8zMDWAgYTDhtvQ49tJ0s2dmrFYSLGAMREz2B91QGWUHMO1TtNv0v3dkXQvTIH1cLvvBjQmvUpaPxm6nV5x90Pd69WJXEvPBgqS9SoDhJYLo3QWpLq4M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737080458; c=relaxed/simple; bh=JBTt/Z9N7iV2G4ysKTG/4TQLBwC2L4Iv5ftPog5zH2M=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e3ljQLHevNOz67CKkDg0gPyK1IUDGxZC7Zj4ZixQaJd1vDf65N5GHStou9NyjJ5rjbbeZUf8QljOWSqnWgwtJLZnUPPyhtDINPzCRvj1W8UWk0pl/XrvTR9h41rUvzF5td8rTJuSn75HVE0XSoMiAG25GJxamA8vDDZrs+G+4ec= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=WdgojwVN; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="WdgojwVN" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=R+0iTCh5BnZffFpeZ7Q9d0IL57elABKcSRb0Ed4n1rY=; b=WdgojwVN2p1xjODo/ipBJE4rzn bg3gKYAimrBl/UTfkCGfrpSlDR+e2rSF05rpXMR9evje4nBRBcXMJe+ma8ZKjW39HNAzKC9IrYwcW Fm9jnAP4cWZ261RT7ayFIEqbSVqAStb9l/JXSmvaRCRv2dyLDwl4HPL7NGApf5UHg+Obhf13J1wrv pLaW5fmleTteTTwQ6p5lM6xGpeGBZaa5vAtA9mepM0U/kXCTrfTmwTfNaon03ukCp2XSkEvFdegJv KrkjqRQklyyah1jjlvYgwYMG5TsqUuMyzyIWJPNvdQICGmqEYhEmzcwPQG1+ZOGAn/t4DE4012mmN /vuRuuSg==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.98 #2 (Red Hat Linux)) id 1tYbyc-00000002pqv-33T6; Fri, 17 Jan 2025 02:20:50 +0000 Date: Fri, 17 Jan 2025 02:20:50 +0000 From: Al Viro To: Andrii Nakryiko Cc: Dave Chinner , Theodore Ts'o , lsf-pc@lists.linux-foundation.org, Linux Filesystem Development List , bpf@vger.kernel.org Subject: Re: [LSF/MM/BPF TOPIC] time to reconsider tracepoints in the vfs? Message-ID: <20250117022050.GO1977892@ZenIV> References: <20250116124949.GA2446417@mit.edu> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro On Thu, Jan 16, 2025 at 01:43:39PM -0800, Andrii Nakryiko wrote: > - relative stability of tracepoints in terms of naming, semantics, > arguments. While not stable APIs, tracepoints are "more stable" in > practice due to more deliberate and strategic placement (usually), so > they tend to get renamed or changed much less frequently. > > So, as far as BPF is concerned, tracepoints are still preferable to > kprobes for something like VFS, and just because BPF can be used with > kprobes easily doesn't mean BPF users don't need useful tracepoints. The problem is, exact same reasons invite their use by LSM-in-BPF and similar projects, and once that happens, the rules regarding stability will bite and bite _hard_. And from what I've seen from the same LSM-in-BPF folks, it won't stay within relatively stable areas - not for long, anyway.