From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83410E7E635 for ; Tue, 26 Sep 2023 13:49:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234854AbjIZNtz (ORCPT ); Tue, 26 Sep 2023 09:49:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44876 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234876AbjIZNty (ORCPT ); Tue, 26 Sep 2023 09:49:54 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6FF510E for ; Tue, 26 Sep 2023 06:49:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695736141; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4a0+/j3wqqmi1vR/kPX5Kqapr51Hnx898rdCOogEsLU=; b=BEzsnhIAJFuHg5/vBw0yXAxQ53zKFrFp2dYvamwG/o/o/YDUfcaYA1HdE2WEVd0C4ylCUH jRhVDyFVQ6ZFpn+npqH65vWdtGs3vdegAZ5qxbJZc1nxxYihEVKaLlnUAeMbapFPDxBN8k IFrkviWQtRzHaln6mIMvpplTC4DeM9A= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-75-td5N-bvqNoevhu9VjagDWQ-1; Tue, 26 Sep 2023 09:48:57 -0400 X-MC-Unique: td5N-bvqNoevhu9VjagDWQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A2B45101A529; Tue, 26 Sep 2023 13:48:56 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.53]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3291A140273D; Tue, 26 Sep 2023 13:48:53 +0000 (UTC) From: Florian Weimer To: Miklos Szeredi Cc: Christian Brauner , Miklos Szeredi , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-man@vger.kernel.org, linux-security-module@vger.kernel.org, Karel Zak , Ian Kent , David Howells , Al Viro , Christian Brauner , Amir Goldstein Subject: Re: [RFC PATCH 2/3] add statmnt(2) syscall References: <20230913152238.905247-1-mszeredi@redhat.com> <20230913152238.905247-3-mszeredi@redhat.com> <20230914-salzig-manifest-f6c3adb1b7b4@brauner> <20230914-lockmittel-verknallen-d1a18d76ba44@brauner> <20230918-grafik-zutreffen-995b321017ae@brauner> Date: Tue, 26 Sep 2023 15:48:51 +0200 In-Reply-To: (Miklos Szeredi's message of "Mon, 18 Sep 2023 16:14:02 +0200") Message-ID: <871qeloxj0.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Precedence: bulk List-ID: * Miklos Szeredi: > On Mon, Sep 18, 2023 at 3:51=E2=80=AFPM Christian Brauner wrote: > >> I really would prefer a properly typed struct and that's what everyone >> was happy with in the session as well. So I would not like to change the >> main parameters. > > I completely agree. Just would like to understand this point: > > struct statmnt *statmnt(u64 mntid, u64 mask, unsigned int flags); > > What's not properly typed about this interface? > > I guess the answer is that it's not a syscall interface, which will > have an added [void *buf, size_t bufsize], while the buffer sizing is > done by a simple libc wrapper. > > Do you think that's a problem? If so, why? Try-and-resize interfaces can be quite bad for data obtained from the network. If the first call provides the minimum buffer size (like getgroups, but unlike readlink or the glibc *_r interfaces for NSS), this could at least allow us to avoid allocating too much. In userspace, we cannot reduce the size of the heap allocation without knowing where the pointers are and what they mean. I also don't quite understand the dislike of variable-sized records. Don't getdents, inotify, Netlink all use them? And I think at least for Netlink, more stuff is added all the time? Thanks, Florian