Date: Mon, 28 Sep 1998 14:13:42 +1000 From: Bruce Evans <bde@zeta.org.au> To: mike@smith.net.au, tmb@rcru.rl.ac.uk Cc: freebsd-current@FreeBSD.ORG Subject: Re: 2048-byte sector support for DOS filesystem. Message-ID: <199809280413.OAA08286@godzilla.zeta.org.au>
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>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
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