From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753417AbbCMVwL (ORCPT ); Fri, 13 Mar 2015 17:52:11 -0400 Received: from mail-lb0-f182.google.com ([209.85.217.182]:45960 "EHLO mail-lb0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751172AbbCMVwJ (ORCPT ); Fri, 13 Mar 2015 17:52:09 -0400 MIME-Version: 1.0 In-Reply-To: <20150313214556.GB10954@cloud> References: <20150313194252.GA10317@cloud> <20150313214556.GB10954@cloud> From: Andy Lutomirski Date: Fri, 13 Mar 2015 14:51:47 -0700 Message-ID: Subject: Re: [PATCH 0/6] CLONE_FD: Task exit notification via file descriptor To: Josh Triplett Cc: David Drysdale , Al Viro , Andrew Morton , Ingo Molnar , Kees Cook , Oleg Nesterov , "Paul E. McKenney" , "H. Peter Anvin" , Rik van Riel , Thomas Gleixner , Thiago Macieira , Michael Kerrisk , "linux-kernel@vger.kernel.org" , Linux API , Linux FS Devel , X86 ML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 13, 2015 at 2:45 PM, wrote: > On Fri, Mar 13, 2015 at 02:33:44PM -0700, Andy Lutomirski wrote: >> On Fri, Mar 13, 2015 at 12:42 PM, Josh Triplett wrote: >> > On Fri, Mar 13, 2015 at 04:05:29PM +0000, David Drysdale wrote: >> >> On Fri, Mar 13, 2015 at 1:40 AM, Josh Triplett wrote: >> >> > This patch series introduces a new clone flag, CLONE_FD, which lets the caller >> >> > handle child process exit notification via a file descriptor rather than >> >> > SIGCHLD. CLONE_FD makes it possible for libraries to safely launch and manage >> >> > child processes on behalf of their caller, *without* taking over process-wide >> >> > SIGCHLD handling (either via signal handler or signalfd). >> >> >> >> Hi Josh, >> >> >> >> From the overall description (i.e. I haven't looked at the code yet) >> >> this looks very interesting. However, it seems to cover a lot of the >> >> same ground as the process descriptor feature that was added to FreeBSD >> >> in 9.x/10.x: >> >> https://www.freebsd.org/cgi/man.cgi?query=pdfork&sektion=2 >> > >> > Interesting. >> > >> >> I think it would ideally be nice for a userspace library developer to be >> >> able to do subprocess management (without SIGCHLD) in a similar way >> >> across both platforms, without lots of complicated autoconf shenanigans. >> >> >> >> So could we look at the overlap and seeing if we can come up with >> >> something that covers your requirements and also allows for something >> >> that looks like FreeBSD's process descriptors? >> > >> > Agreed; however, I think it's reasonable to provide appropriate Linux >> > system calls, and then let glibc or libbsd or similar provide the >> > BSD-compatible calls on top of those. I don't think the kernel >> > interface needs to exactly match FreeBSD's, as long as it's a superset >> > of the functionality. >> >> We need to be careful with things like read(2), though. It's hard to >> write a glibc function that makes read(2) do something other than what >> the kernel thinks. Similarly, poll(2) is defined by the kernel. It >> would be really nice to be consistent here. > > It doesn't sound like FreeBSD implements read(2) on the pdfork file > descriptor at all. If it does, yes, we're not going to be able to be > compatible with that. There's an argument that using read(2) for stuff like this is a bad idea. If anyone tried to do this in C++ (or any other OO language): class GenericInterface { public: virtual void DoAction(const char *value, size_t len) = 0; }; class Process : public GenericInterface { public: virtual void DoAction(const char *value, size_t len) = 0; }; void Kill(Process *p) { p->DoAction("kill", 4); }; They'd be re-educated very quickly. This is like duck typing, but taken to a whole new level: *everything* is a duck, and ducks have a grand total of three operations. On the other hand, this seems to be UNIX tradition. It's not as if using echo on pidfds is going to be a common idiom, though. In any event, we should find out what FreeBSD does in response to read(2) on the fd. --Andy From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [PATCH 0/6] CLONE_FD: Task exit notification via file descriptor Date: Fri, 13 Mar 2015 14:51:47 -0700 Message-ID: References: <20150313194252.GA10317@cloud> <20150313214556.GB10954@cloud> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: David Drysdale , Al Viro , Andrew Morton , Ingo Molnar , Kees Cook , Oleg Nesterov , "Paul E. McKenney" , "H. Peter Anvin" , Rik van Riel , Thomas Gleixner , Thiago Macieira , Michael Kerrisk , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Linux API , Linux FS Devel , X86 ML To: Josh Triplett Return-path: In-Reply-To: <20150313214556.GB10954@cloud> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Fri, Mar 13, 2015 at 2:45 PM, wrote: > On Fri, Mar 13, 2015 at 02:33:44PM -0700, Andy Lutomirski wrote: >> On Fri, Mar 13, 2015 at 12:42 PM, Josh Triplett wrote: >> > On Fri, Mar 13, 2015 at 04:05:29PM +0000, David Drysdale wrote: >> >> On Fri, Mar 13, 2015 at 1:40 AM, Josh Triplett wrote: >> >> > This patch series introduces a new clone flag, CLONE_FD, which lets the caller >> >> > handle child process exit notification via a file descriptor rather than >> >> > SIGCHLD. CLONE_FD makes it possible for libraries to safely launch and manage >> >> > child processes on behalf of their caller, *without* taking over process-wide >> >> > SIGCHLD handling (either via signal handler or signalfd). >> >> >> >> Hi Josh, >> >> >> >> From the overall description (i.e. I haven't looked at the code yet) >> >> this looks very interesting. However, it seems to cover a lot of the >> >> same ground as the process descriptor feature that was added to FreeBSD >> >> in 9.x/10.x: >> >> https://www.freebsd.org/cgi/man.cgi?query=pdfork&sektion=2 >> > >> > Interesting. >> > >> >> I think it would ideally be nice for a userspace library developer to be >> >> able to do subprocess management (without SIGCHLD) in a similar way >> >> across both platforms, without lots of complicated autoconf shenanigans. >> >> >> >> So could we look at the overlap and seeing if we can come up with >> >> something that covers your requirements and also allows for something >> >> that looks like FreeBSD's process descriptors? >> > >> > Agreed; however, I think it's reasonable to provide appropriate Linux >> > system calls, and then let glibc or libbsd or similar provide the >> > BSD-compatible calls on top of those. I don't think the kernel >> > interface needs to exactly match FreeBSD's, as long as it's a superset >> > of the functionality. >> >> We need to be careful with things like read(2), though. It's hard to >> write a glibc function that makes read(2) do something other than what >> the kernel thinks. Similarly, poll(2) is defined by the kernel. It >> would be really nice to be consistent here. > > It doesn't sound like FreeBSD implements read(2) on the pdfork file > descriptor at all. If it does, yes, we're not going to be able to be > compatible with that. There's an argument that using read(2) for stuff like this is a bad idea. If anyone tried to do this in C++ (or any other OO language): class GenericInterface { public: virtual void DoAction(const char *value, size_t len) = 0; }; class Process : public GenericInterface { public: virtual void DoAction(const char *value, size_t len) = 0; }; void Kill(Process *p) { p->DoAction("kill", 4); }; They'd be re-educated very quickly. This is like duck typing, but taken to a whole new level: *everything* is a duck, and ducks have a grand total of three operations. On the other hand, this seems to be UNIX tradition. It's not as if using echo on pidfds is going to be a common idiom, though. In any event, we should find out what FreeBSD does in response to read(2) on the fd. --Andy