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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E3D4C3A5A7 for ; Wed, 28 Aug 2019 15:55:56 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 75BF32064A for ; Wed, 28 Aug 2019 15:55:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="VGRi8Mk2"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="pqTccn5J" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 75BF32064A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Date:To:From:Subject:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=HSRejY/IPv/i3uaHyzBvbZHY5fjqf0llHOKx57GdUTI=; b=VGRi8Mk2wv62ZD uqV/uRc0EY9bAd7k6gSqFsCfsIgRDoJEr2AsOai+2mtN46Z22ezYvaXEsvqFmpLdXIwVARRprOb8E KSiuvmGi9eUO9oGJ/E0HGjClIIXKsGctEZXBXTjiMzJRzz+ZkeTMa3z/nx1g6dpPyI8tqZy/+QSsp oUMK91/uOtkwT9fBNQs7I4ow3NR3gGJyasMxId/rZ7T1JDwkKXXJK86LYODquU5TFUfMSDKV3TLHA wfSUtjQCpoxbX3w9iMjeDM/V3AILpkKqYpdqJTwWdpaXaKFltV6DhQ76/kat1xAcT5jIp2k729YjT jIYMplEt2kUZK+jz40QQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i30Ie-0007KK-3a; Wed, 28 Aug 2019 15:55:56 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1i30Ia-0007J7-Mk for linux-arm-kernel@lists.infradead.org; Wed, 28 Aug 2019 15:55:54 +0000 Received: from tleilax.poochiereds.net (68-20-15-154.lightspeed.rlghnc.sbcglobal.net [68.20.15.154]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 765322064A; Wed, 28 Aug 2019 15:55:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567007749; bh=tm23iPOHz5qNiVmbKBRthv6o0H14qpr8dY7bd4MTQKs=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=pqTccn5JcnucNCAhPvukewbhK7LnqfZiA1JhrrT1FDFY4mCrVB8AZyQ8GN7mLjP8y 7s9EDdOPkKuIVFWDEaVrPbihjrm8teyPYUCsz+WciUJXkEpW4kr0ySk55f/ASUGrn8 zpEFoJeA5Hy5XDMtaE0vrkdWUVKHa2wWQhJO2xxg= Message-ID: <4da231cd52880991d8a038adb8fbb2ef3d724db9.camel@kernel.org> Subject: Re: [PATCH RESEND v11 7/8] open: openat2(2) syscall From: Jeff Layton To: sbaugh@catern.com, linux-fsdevel@vger.kernel.org Date: Wed, 28 Aug 2019 11:55:47 -0400 In-Reply-To: <854l2366zp.fsf@catern.com> References: <20190820033406.29796-1-cyphar@cyphar.com> <20190820033406.29796-8-cyphar@cyphar.com> <854l2366zp.fsf@catern.com> User-Agent: Evolution 3.32.4 (3.32.4-1.fc30) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190828_085552_766294_04D6F40B X-CRM114-Status: GOOD ( 19.07 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, linux-sh@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@ozlabs.org, linux-alpha@vger.kernel.org, sparclinux@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 2019-08-26 at 19:50 +0000, sbaugh@catern.com wrote: > Aleksa Sarai writes: > > To this end, we introduce the openat2(2) syscall. It provides all of the > > features of openat(2) through the @how->flags argument, but also > > also provides a new @how->resolve argument which exposes RESOLVE_* flags > > that map to our new LOOKUP_* flags. It also eliminates the long-standing > > ugliness of variadic-open(2) by embedding it in a struct. > > I don't like this usage of a structure in memory to pass arguments that > would fit in registers. This would be quite inconvenient for me as a > userspace developer. > > Others have brought up issues with this: the issue of seccomp, and the > issue of mismatch between the userspace interface and the kernel > interface, are the most important for me. I want to add another, > admittedly somewhat niche, concern. > > This interfaces requires a program to allocate memory (even on the > stack) just to pass arguments to the kernel which could be passed > without allocating that memory. That makes it more difficult and less > efficient to use this syscall in any case where memory is not so easily > allocatable: such as early program startup or assembly, where the stack > may be limited in size or not even available yet, or when injecting a > syscall while ptracing. > > A struct-passing interface was needed for clone, since we ran out of > registers; but we have not run out of registers yet for openat, so it > would be nice to avoid this if we can. We can always expand later... > We can't really expand later like you suggest. Suppose in a couple of years that we need to add some new argument to openat2 that isn't just a new flag. If all these values are passed by individual arguments, you can't add one later without adding yet another syscall. Using a struct for this allows this to be extended later, OTOH. You can extend it, and add a flag that tells the kernel that it can access the new field. No new syscall required. -- Jeff Layton _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel