Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751911AbaJSUy1 (ORCPT ); Sun, 19 Oct 2014 16:54:27 -0400 Received: from terminus.zytor.com ([198.137.202.10]:34985 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751092AbaJSUyY (ORCPT ); Sun, 19 Oct 2014 16:54:24 -0400 Message-ID: <544424E6.1060002@zytor.com> Date: Sun, 19 Oct 2014 13:53:58 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.1 MIME-Version: 1.0 To: Al Viro , Andy Lutomirski CC: David Drysdale , "Eric W. Biederman" , Meredydd Luff , "linux-kernel@vger.kernel.org" , Thomas Gleixner , Ingo Molnar , Andrew Morton , Kees Cook , Arnd Bergmann , X86 ML , linux-arch , Linux API Subject: Re: [PATCHv4 RESEND 0/3] syscalls,x86: Add execveat() system call References: <1401975635-6162-1-git-send-email-drysdale@google.com> <20141019202034.GH7996@ZenIV.linux.org.uk> In-Reply-To: <20141019202034.GH7996@ZenIV.linux.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/19/2014 01:20 PM, Al Viro wrote: > On Fri, Oct 17, 2014 at 02:45:03PM -0700, Andy Lutomirski wrote: > >> For example, I want to be able to reliably do something like nsenter >> --namespace-flags-here toybox sh. Toybox's shell is unusual in that >> it is more or less fully functional, so this should Just Work (tm), >> except that the toybox binary might not exist in the namespace being >> entered. If execveat were available, I could rig nsenter or a similar >> tool to open it with O_CLOEXEC, enter the namespace, and then call >> execveat. > > The question I hadn't seen really answered through all of that was how to > deal with #!... "Just use d_path()" isn't particulary appealing - if that > file has a pathname reachable for you, you could bloody well use _that_ > from the very beginning. > > Frankly, I wonder if it would make sense to provide something like > dupfs. We can't mount it by default on /dev/fd (more's the pity), but > it might be a good thing to have. > > What it is, for those who are not familiar with Plan 9: a filesystem with > one directory and a bunch of files in it. Directory contents depends on > who's looking; for each opened descriptor in your descriptor table, you'll > see two files there. One series is 0, 1, ... - opening one of those gives > dup(). IOW, it's *not* giving you a new struct file; it gives you a new > reference to existing one, complete with sharing IO position, etc. Another > is 0ctl, 1ctl, ... - those are read-only and reading from them gives pretty > much a combination of our /proc/self/fdinfo/n with readlink of /proc/self/fd/n. > > It's actually a better match for what one would expect at /dev/fd than what > we do. Example: > Yes, it is really unfortunate that /proc/self/fd/* had the wrong semantics for the start, due to then-existing implementation issues. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/