From owner-freebsd-arch Tue Mar 12 13:56:34 2002 Delivered-To: freebsd-arch@freebsd.org Received: from mail.rpi.edu (mail.rpi.edu [128.113.22.40]) by hub.freebsd.org (Postfix) with ESMTP id B003337B488; Tue, 12 Mar 2002 13:56:23 -0800 (PST) Received: from [128.113.24.47] (gilead.acs.rpi.edu [128.113.24.47]) by mail.rpi.edu (8.12.1/8.12.1) with ESMTP id g2CLuLpu095490; Tue, 12 Mar 2002 16:56:21 -0500 Mime-Version: 1.0 X-Sender: drosih@mail.rpi.edu Message-Id: In-Reply-To: <3C8E6AC0.A51444E1@mindspring.com> References: <60373.1015917340@critter.freebsd.dk> <3C8E6AC0.A51444E1@mindspring.com> Date: Tue, 12 Mar 2002 16:56:20 -0500 To: Terry Lambert From: Garance A Drosihn Subject: Re: Increasing the size of dev_t and ino_t Cc: Poul-Henning Kamp , Harti Brandt , Robert Watson , Julian Elischer , arch@FreeBSD.ORG Content-Type: text/plain; charset="us-ascii" ; format="flowed" X-Scanned-By: MIMEDefang 2.3 (www dot roaringpenguin dot com slash mimedefang) Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG At 12:53 PM -0800 3/12/02, Terry Lambert wrote: >Garance A Drosihn wrote: >> Now for suggestion part #2: >> >> Once we get to a 64-bit (u)dev_t, we could reserve one byte of >> that for the "type of filesystem" (loosely speaking). A value > > of 0 for local hard disks > > 3 for OpenAFS or ARLA mounted > > 4 for CODA-mounted [...etc...] > >man statfs. > >The answer is that it's possible to get the FS mount type >already. This would not be to get the fs mount type, it would be to avoid duplicate values for st_dev. By using one byte to explicitly indicate the "pool of numbers" one is picking values for, each "pool" can pick whatever values it wants for the remaining bits. Thus we could use the creation-date of a hard-disk filesystem for dev_t in the case of hard disks (if we wanted to), and not have to worry that it might be the same as some id in AFS-land. This is an implementation detail of how to ensure a unique value for st_dev, when we're talking about billions of such values (in the case of AFS or Coda). This is not something we would document for use in any userland-level code. -- Garance Alistair Drosehn = gad@eclipse.acs.rpi.edu Senior Systems Programmer or gad@freebsd.org Rensselaer Polytechnic Institute or drosih@rpi.edu To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message