From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: io_uring vs in_compat_syscall() Date: Wed, 22 Jul 2020 08:30:50 +0200 Message-ID: <20200722063050.GA24968@lst.de> References: <8987E376-6B13-4798-BDBA-616A457447CF@amacapital.net> <20200721070709.GB11432@lst.de> <20200721143412.GA8099@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andy Lutomirski Cc: Christoph Hellwig , Jens Axboe , linux-arch , Linux API , LKML , io-uring-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-arch.vger.kernel.org On Tue, Jul 21, 2020 at 10:25:24AM -0700, Andy Lutomirski wrote: > On Tue, Jul 21, 2020 at 7:34 AM Christoph Hellwig wrote: > > > > On Tue, Jul 21, 2020 at 07:31:02AM -0700, Andy Lutomirski wrote: > > > > What do you mean with "properly wired up". Do you really want to spread > > > > ->compat_foo methods everywhere, including read and write? I found > > > > in_compat_syscall() a lot small and easier to maintain than all the > > > > separate compat cruft. > > > > > > I was imagining using a flag. Some of the net code uses > > > MSG_CMSG_COMPAT for this purpose. > > > > Killing that nightmarish monster is what actually got me into looking > > io_uring and starting this thread. > > I agree that MSG_CMSG_COMPAT is nasty, but I think the concept is > sound -- rather than tracking whether we're compat by using a > different function or a per-thread variable, actually explicitly > tracking the mode seems sensible. I very strongly disagree. Two recent projects I did was to remove the compat_exec mess, and the compat get/setsockopt mess, and each time it removed hundreds of lines of code duplicating native functionality, often in slightly broken ways. We need a generic out of band way to transfer the information down and just check in in a few strategic places, and in_compat_syscall() does the right thing for that. > If we're going to play in_compat_syscall() games, let's please make > io_uring_enter() return -EINVAL if in_compat_syscall() != ctx->compat. That sounds like a plan, but still doesn't help with submissions from the offload WQ or the sqpoll thread. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from verein.lst.de ([213.95.11.211]:54974 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728649AbgGVGay (ORCPT ); Wed, 22 Jul 2020 02:30:54 -0400 Date: Wed, 22 Jul 2020 08:30:50 +0200 From: Christoph Hellwig Subject: Re: io_uring vs in_compat_syscall() Message-ID: <20200722063050.GA24968@lst.de> References: <8987E376-6B13-4798-BDBA-616A457447CF@amacapital.net> <20200721070709.GB11432@lst.de> <20200721143412.GA8099@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andy Lutomirski Cc: Christoph Hellwig , Jens Axboe , linux-arch , Linux API , LKML , io-uring@vger.kernel.org Message-ID: <20200722063050.Mt_q5eGXqrKHWy_mFcLVDWT6l5bHHvB3ho6cPERJNps@z> On Tue, Jul 21, 2020 at 10:25:24AM -0700, Andy Lutomirski wrote: > On Tue, Jul 21, 2020 at 7:34 AM Christoph Hellwig wrote: > > > > On Tue, Jul 21, 2020 at 07:31:02AM -0700, Andy Lutomirski wrote: > > > > What do you mean with "properly wired up". Do you really want to spread > > > > ->compat_foo methods everywhere, including read and write? I found > > > > in_compat_syscall() a lot small and easier to maintain than all the > > > > separate compat cruft. > > > > > > I was imagining using a flag. Some of the net code uses > > > MSG_CMSG_COMPAT for this purpose. > > > > Killing that nightmarish monster is what actually got me into looking > > io_uring and starting this thread. > > I agree that MSG_CMSG_COMPAT is nasty, but I think the concept is > sound -- rather than tracking whether we're compat by using a > different function or a per-thread variable, actually explicitly > tracking the mode seems sensible. I very strongly disagree. Two recent projects I did was to remove the compat_exec mess, and the compat get/setsockopt mess, and each time it removed hundreds of lines of code duplicating native functionality, often in slightly broken ways. We need a generic out of band way to transfer the information down and just check in in a few strategic places, and in_compat_syscall() does the right thing for that. > If we're going to play in_compat_syscall() games, let's please make > io_uring_enter() return -EINVAL if in_compat_syscall() != ctx->compat. That sounds like a plan, but still doesn't help with submissions from the offload WQ or the sqpoll thread.