Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754436AbbGBSsP (ORCPT ); Thu, 2 Jul 2015 14:48:15 -0400 Received: from cantor2.suse.de ([195.135.220.15]:60488 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754248AbbGBSsE (ORCPT ); Thu, 2 Jul 2015 14:48:04 -0400 Message-ID: <1435862819.1749.1.camel@suse.com> Subject: Re: [Spice-devel] [RFC PATCH 1/1] Add a usbredir kernel module to remotely connect USB devices over IP. From: Oliver Neukum To: Jeremy White Cc: Hans de Goede , "Daniel P. Berrange" , spice-devel@lists.freedesktop.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 02 Jul 2015 20:46:59 +0200 In-Reply-To: <55955F4F.4050500@codeweavers.com> References: <1435700650-640-1-git-send-email-jwhite@codeweavers.com> <1435700650-640-2-git-send-email-jwhite@codeweavers.com> <20150701090619.GB16822@redhat.com> <1435826719.13145.10.camel@suse.com> <559521E5.2090400@redhat.com> <1435839045.2424.9.camel@suse.com> <55955F4F.4050500@codeweavers.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2484 Lines: 58 On Thu, 2015-07-02 at 10:57 -0500, Jeremy White wrote: > On 07/02/2015 07:10 AM, Oliver Neukum wrote: > > On Thu, 2015-07-02 at 13:35 +0200, Hans de Goede wrote: > >> Hi, > >> > >> On 02-07-15 10:45, Oliver Neukum wrote: > >>> On Wed, 2015-07-01 at 10:06 +0100, Daniel P. Berrange wrote: > >>> > >>>> I don't really think it is sensible to be defining & implementing new > >>>> network services which can't support strong encryption and authentication. > >>>> Rather than passing the file descriptor to the kernel and having it do > >>>> the I/O directly, I think it would be better to dissassociate the kernel > >>>> from the network transport, and thus leave all sockets layer data I/O > >>>> to userspace daemons so they can layer in TLS or SASL or whatever else > >>>> is appropriate for the security need. > >>> > >>> Hi, > >>> > >>> this hits a fundamental limit. Block IO must be done entirely in kernel > >>> space or the system will deadlock. The USB stack is part of the block > >>> layer and the SCSI error handling. Thus if you involve user space you > >>> cannot honor memory allocation with GFP_NOFS and you break all APIs > >>> where we pass GFP_NOIO in the USB stack. > >>> > >>> Supposed you need to reset a storage device for error handling. > >>> Your user space programm does a syscall, which allocates memory > >>> and needs to launder pages. It proceeds to write to the storage device > >>> you wish to reset. > >>> > >>> It is the same problem FUSE has with writable mmap. You cannot do > >>> block devices in user space sanely. > >> > >> So how is this dealt with for usbip ? > > > > As far as I can tell, it isn't. Running a storage device over usbip > > is a bit dangerous. > > I don't follow that analysis. The usbip interactions with the usb stack > all seem to be atomic, and never trigger a syscall, as far as I can > tell. A port reset will flip a few bits and return. A urb enqueue > queues and wakes a different thread, and returns. The alternate thread > performs the sendmsg. > > I'm not suggesting that running a storage device over usbip is > especially safe, but I don't see the limit on the design. Are you referring to the current code or the proposed user space pipe? Regards Oliver -- 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/