From owner-cvs-all Sun Sep 19 12:24:35 1999 Delivered-To: cvs-all@freebsd.org Received: from proxy2.ba.best.com (proxy2.ba.best.com [206.184.139.14]) by hub.freebsd.org (Postfix) with ESMTP id D901A152BA; Sun, 19 Sep 1999 12:24:28 -0700 (PDT) (envelope-from dillon@apollo.backplane.com) Received: from apollo.backplane.com ([209.157.86.2]) by proxy2.ba.best.com (8.9.3/8.9.2/best.out) with ESMTP id MAA11580; Sun, 19 Sep 1999 12:22:50 -0700 (PDT) Received: (from dillon@localhost) by apollo.backplane.com (8.9.3/8.9.1) id MAA74009; Sun, 19 Sep 1999 12:22:50 -0700 (PDT) (envelope-from dillon) Date: Sun, 19 Sep 1999 12:22:50 -0700 (PDT) From: Matthew Dillon Message-Id: <199909191922.MAA74009@apollo.backplane.com> To: Poul-Henning Kamp Cc: Matthew Jacob , dg@root.com, Greg Lehey , cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: User block device access References: <17519.937768020@critter.freebsd.dk> Sender: owner-cvs-all@FreeBSD.ORG Precedence: bulk :In message <199909191900.MAA73792@apollo.backplane.com>, Matthew Dillon writes: : :> In fact, a memory-mappable buffered block device with write-through would :> be much, much more useful to a database then a character device, and I :> think it's only a two line patch to make mmap() work, and probably a :> four line patch to implement write-through. It would be virtually :> unbeatable... use of mmap() removes the extra copy overhead, read-caching :> takes the burden off the application, optional write-through gives you :> instant feedback *AND* reblocking. I would even be willing to make the :> write-through the default. :> :> That would give us an extremely powerful and useful buffered block device :> implementation. : :So you are saying that we could basically leave read/write as they :are for cdevs and provide the buffer/cache mechanisms with mmap ? : :-- :Poul-Henning Kamp FreeBSD coreteam member :phk@FreeBSD.ORG "Real hackers run -current on their laptop." We cannot really implement mmap for cdev's that aren't direct memory maps (such as video frame buffers), at least not without breaking cache coherency. We *can* implement mmap for bdev's and we *can* change the way writes to bdev's work. Matthew Dillon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message