From owner-freebsd-arch Sun Dec 3 20: 7:18 2000 From owner-freebsd-arch@FreeBSD.ORG Sun Dec 3 20:07:16 2000 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from earth.backplane.com (placeholder-dcat-1076843399.broadbandoffice.net [64.47.83.135]) by hub.freebsd.org (Postfix) with ESMTP id 6F5A537B400 for ; Sun, 3 Dec 2000 20:07:16 -0800 (PST) Received: (from dillon@localhost) by earth.backplane.com (8.11.1/8.9.3) id eB446jk70007; Sun, 3 Dec 2000 20:06:45 -0800 (PST) (envelope-from dillon) Date: Sun, 3 Dec 2000 20:06:45 -0800 (PST) From: Matt Dillon Message-Id: <200012040406.eB446jk70007@earth.backplane.com> To: Andrew Gallatin Cc: Peter Wemm , "Kenneth D. Merry" , arch@FreeBSD.ORG Subject: Re: zero copy code review References: <20001129231653.A1503@panzer.kdm.org> <200012040308.eB438tD52326@mobile.wemm.org> <14891.4047.626648.658103@grasshopper.cs.duke.edu> Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG :freed). We do not make anything COW for the kernel. : : > either, but I could have missed it.. What about drivers that DMA to pages : > mapped into KVM without checking writability (and hence COW)? : :This is a good point. But I cannot think of any circumstance where a :driver would be DMA'ing directly to a user owned page (with the :exception of a vm fault, but this is impossible because the pages are :resident prior to setting up the send and are wired for the duration :of the send). : :Thanks for the input. I'm glad to see you and Matt looking at this! : :Drew Careful. If you read() from a raw device most disk drivers WILL dma directly to a user-owned page. -Matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message