From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO Date: Mon, 15 Dec 2008 08:23:12 +0200 Message-ID: <4945F7D0.1070200@redhat.com> References: <49456337.4000000@redhat.com> <494591F7.3080002@codemonkey.ws> <200812150057.10162.paul@codesourcery.com> <4945BC63.1080600@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Paul Brook , qemu-devel@nongnu.org, Andrea Arcangeli , chrisw@redhat.com, kvm@vger.kernel.org, Gerd Hoffmann To: Anthony Liguori Return-path: Received: from mx2.redhat.com ([66.187.237.31]:43192 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751080AbYLOGZG (ORCPT ); Mon, 15 Dec 2008 01:25:06 -0500 In-Reply-To: <4945BC63.1080600@codemonkey.ws> Sender: kvm-owner@vger.kernel.org List-ID: Anthony Liguori wrote: >> >> I Wouldn't be surprised if some machines had a large memory mapped IO >> space. Most of it might not be actively used, but once you start >> considering 64-bit machines on 32-bit hosts these allocations would >> become problematic. >> > > At some level, any DMA API would fall apart here. Certain IO > operations simply cannot be split (such as network send). If you pass > don't pass a flag to the map function that says you can handle partial > results, you must cope with map() returning NULL (by dropping the > packet). > ... and then you must cope with it. In all non-network dma clients. Or in the dma api. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.