Date: Sat, 21 Feb 2004 15:16:08 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: John-Mark Gurney <gurney_j@efn.org> Cc: Aaron Peterson <aaron@alpete.com> Subject: Re: bcwipe won't wipe a block device... Message-ID: <20040221145653.L7690@gamplex.bde.org> In-Reply-To: <20040220183634.GK85686@funkthat.com> References: <9615.162.114.211.143.1077213472.squirrel@mail.alpete.com> <29352.162.114.211.143.1077222503.squirrel@mail.alpete.com> <20040219204012.GA33771@troutmask.apl.washington.edu> <46490.162.114.211.143.1077223809.squirrel@mail.alpete.com> <20040220183634.GK85686@funkthat.com>
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On Fri, 20 Feb 2004, John-Mark Gurney wrote:
> Peter Jeremy wrote this message on Fri, Feb 20, 2004 at 18:23 +1100:
> > Summary: bcwipe is trying to read 1 byte from an offset of 2^N-1.
> > FreeBSD no longer has block devices (since 4.0) - /dev/da0 is a
> > character device. Character devices can only be read in blocksize
> > units (typically 512 bytes for disks). You need to fix bcwipe to
> > handle character devices.
>
> this can be done by using the fstat call on the device node.. it will
> provide both the proper block size (so it'll work w/ md swap backed
> devices that have a 4k block size) and device size...
Um, this can not be done by using the fstat call on the device node.
fstat() on devices always gives 0 for the device size and is little
better for the block size. The block size is always the nominal
value PAGE_SIZE for non-disk devices and is not always the nominal
value BLKDEV_IOSIZE for disk devices. From vfs_vnops.c:
% } else if (vn_isdisk(vp, NULL)) {
% sb->st_blksize = vp->v_rdev->si_bsize_best;
% if (sb->st_blksize < vp->v_rdev->si_bsize_phys)
% sb->st_blksize = vp->v_rdev->si_bsize_phys;
% if (sb->st_blksize < BLKDEV_IOSIZE)
% sb->st_blksize = BLKDEV_IOSIZE;
% } else {
% sb->st_blksize = PAGE_SIZE;
% }
Here si_bsize_phys is the sector size of drivers or GEOM set it, else
it is defaulted to DEV_BSIZE in spec_open(). si_bsize_bestt is fully
rotted garbage -- it is only used above, but never set except using
bzero() to 0. Since sector sizes are normally smaller than BLKDEV_IOSIZE
and BLKDEV_IOSIZE is normally PAGE_SIZE, the above normally sets
st_blksize to PAGE_SIZE for all devices.
Bruce
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