From owner-freebsd-current  Sun Sep 27 21:14:14 1998
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Received: (from majordom@localhost)
          by hub.freebsd.org (8.8.8/8.8.8) id VAA25064
          for freebsd-current-outgoing; Sun, 27 Sep 1998 21:14:14 -0700 (PDT)
          (envelope-from owner-freebsd-current@FreeBSD.ORG)
Received: from godzilla.zeta.org.au (godzilla.zeta.org.au [203.15.68.22])
          by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id VAA25027
          for <freebsd-current@FreeBSD.ORG>; Sun, 27 Sep 1998 21:14:04 -0700 (PDT)
          (envelope-from bde@godzilla.zeta.org.au)
Received: (from bde@localhost)
	by godzilla.zeta.org.au (8.8.7/8.8.7) id OAA08286;
	Mon, 28 Sep 1998 14:13:42 +1000
Date: Mon, 28 Sep 1998 14:13:42 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199809280413.OAA08286@godzilla.zeta.org.au>
To: mike@smith.net.au, tmb@rcru.rl.ac.uk
Subject: Re: 2048-byte sector support for DOS filesystem.
Cc: freebsd-current@FreeBSD.ORG
Sender: owner-freebsd-current@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

>As Bruce pointed out, the only thing 'msdosfs' doesn't use an 
>arbitrary sector size for is reading the boot sector. i.e.
>
>/*      $Id: msdosfs_vfsops.c,v 1.36 1998/09/07 13:17:02 bde Exp $ */
>/*      $NetBSD: msdosfs_vfsops.c,v 1.51 1997/11/17 15:36:58 ws Exp $   */
>[intervening bits deleted ]
>        /*
>         * Read the boot sector of the filesystem, and then check the
>         * boot signature.  If not a dos boot sector then error out.
>         */
>#ifdef  PC98
>        error = bread(devvp, 0, 1024, NOCRED, &bp);
>#else
>        error = bread(devvp, 0, 512, NOCRED, &bp);
>#endif
>
>After reading the code, I realized that the physical sector
>block size is currently only available *after* the boot sector
>is read, so I'm not really sure what the answer is.  Presumably
>the sector size is available from some other low-level bit of 
>SCSI/CAM code, but I'm not sure what the appropriate way to get at 
>it is.
>
>Any suggestions?

(a) Always use 2048 or larger.
(b) Get the sector size using the DIOCGPART ioctl().  Using ioctls
    in the kernel is a kludge, but other mount routines already use
    this ioctl precisely to get the sector size.  See ffs_mountfs().

Bruce

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message