ports/63354: bcwipe does not act successfully on raw devices
Aaron Peterson
aaron at alpete.com
Wed Feb 25 15:50:11 UTC 2004
>Number: 63354
>Category: ports
>Synopsis: bcwipe does not act successfully on raw devices
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-ports-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Feb 25 07:50:11 PST 2004
>Closed-Date:
>Last-Modified:
>Originator: Aaron Peterson
>Release: 5.2
>Organization:
KY Cabinet for Health Services
>Environment:
FreeBSD fbsd52.state.ky.us 5.2-RELEASE FreeBSD 5.2-RELEASE #0: Sun Jan 11 04:21:45 GMT 2004 root at wv1u.btc.adaptec.com:/usr/obj/usr/src/sys/GENERIC i386
>Description:
the bcwipe port seems to work as expected on files, but errors when asked to act on a raw device. Discussion on freebsd-current mailing list suggests this has to do with bcwipe expecting to act on a block device, when freebsd 5.2 no longer has block devices, only character devices. I don't even know the difference between the two, so I'm just repeating here. the subject of mail in this thread on freebsd-current was "bcwipe won't wipe a block device"
>How-To-Repeat:
ask bcwipe to wipe a block device per the example in the man page:
bcwipe -bvmd /dev/fd0
or in my case, acting on a portable usb drive:
bcwipe -bvmd /dev/da0
kdump/ktrace of this command on my system can be found here:
http://alpete.com/bcwipe.kdump.txt
>Fix:
The final post in this thread on freebsd-current suggested the following:
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
>Release-Note:
>Audit-Trail:
>Unformatted:
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