From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751424AbaLCDkX (ORCPT ); Tue, 2 Dec 2014 22:40:23 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:42968 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750963AbaLCDkW (ORCPT ); Tue, 2 Dec 2014 22:40:22 -0500 Date: Wed, 3 Dec 2014 03:40:20 +0000 From: Al Viro To: Alex Dubov Cc: "linux-kernel@vger.kernel.org" , Alex Dubov Subject: Re: [PATCH 1/2] fs: introduce sendfd() syscall Message-ID: <20141203034020.GI29748@ZenIV.linux.org.uk> References: <1417494919-4577-1-git-send-email-oakad@yahoo.com> <1417494919-4577-2-git-send-email-oakad@yahoo.com> <20141202170037.GG29748@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 03, 2014 at 01:22:33PM +1100, Alex Dubov wrote: > On a less related note, I hope you will agree that the simpler > mechanism for this very in-demand feature is long overdue on Linux > (every man and his dog are passing fds around these days). ... and I'm less than sure that it's a good thing. If nothing else, once the pieces of your program are passing descriptors around freely, you have created a barfball that will be impossible to split between several boxen if you run into scalability issues. Descriptor-passing is limited to a single system; you *can't* do that between e.g. components of a cluster. So it's not an unmixed blessing, just as overuse of shared memory segments, etc. They do have their uses, but that needs to be carefully considered every time, or you'll create a major headache a few years down the road.