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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 D38F9C3A59F for ; Tue, 27 Aug 2019 00:23:30 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 5FED22080C for ; Tue, 27 Aug 2019 00:23:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5FED22080C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=catern.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 46HV340ZLBzDqY7 for ; Tue, 27 Aug 2019 10:23:28 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 46HNfP4WxkzDqWQ for ; Tue, 27 Aug 2019 06:20:13 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=fail (p=none dis=none) header.from=catern.com Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) by bilbo.ozlabs.org (Postfix) with ESMTP id 46HNfN4nNYz8vhn for ; Tue, 27 Aug 2019 06:20:12 +1000 (AEST) Received: by ozlabs.org (Postfix) id 46HNfN2PHsz9sMr; Tue, 27 Aug 2019 06:20:12 +1000 (AEST) Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=m.gmane.org (client-ip=195.159.176.226; helo=blaine.gmane.org; envelope-from=glppd-linuxppc64-dev@m.gmane.org; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=catern.com X-Greylist: delayed 903 seconds by postgrey-1.36 at bilbo; Tue, 27 Aug 2019 06:20:11 AEST Received: from blaine.gmane.org (195-159-176-226.customer.powertech.no [195.159.176.226]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 46HNfM5sfxz9sML for ; Tue, 27 Aug 2019 06:20:11 +1000 (AEST) Received: from list by blaine.gmane.org with local (Exim 4.89) (envelope-from ) id 1i2LEc-000X1s-An for linuxppc-dev@ozlabs.org; Mon, 26 Aug 2019 22:05:02 +0200 X-Injected-Via-Gmane: http://gmane.org/ To: linuxppc-dev@ozlabs.org From: sbaugh@catern.com Subject: Re: [PATCH RESEND v11 7/8] open: openat2(2) syscall Date: Mon, 26 Aug 2019 19:50:50 +0000 Message-ID: <854l2366zp.fsf@catern.com> References: <20190820033406.29796-1-cyphar@cyphar.com> <20190820033406.29796-8-cyphar@cyphar.com> Mime-Version: 1.0 Content-Type: text/plain User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) Cancel-Lock: sha1:ym8TD2+JE56rxevrCvTf9T8Ptcg= X-Mailman-Approved-At: Tue, 27 Aug 2019 10:19:41 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List 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, sparclinux@vger.kernel.org, linux-alpha@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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...