On 7/25/19 7:14 PM, Zhi-Qiang Lei wrote:
On Jul 25, 2019, at 10:24 PM, gwes <g...@oat.com> wrote:
On 7/24/19 10:19 PM, Zhi-Qiang Lei wrote:
Hi, I’m trying to encrypt a DVD-RAM before putting some files onto it on my
OpenBSD 6.5 desktop. But neither dd nor disklabel seems able to work on the
drive. Did I miss something?
$ dmesg | grep cd
cd0 at scsibus3 targ 1 lun 0: <HL-DT-ST, BD-RE BU40N, FR07> ATAPI 5/cdrom
removable serial.13fd3940302020202020
cd0 at scsibus3 targ 1 lun 0: <HL-DT-ST, BD-RE BU40N, FR07> ATAPI 5/cdrom
removable serial.13fd3940302020202020
$ doas dd if=/dev/urandom of=/dev/rcd0c bs=1k
dd: /dev/rcd0c: Invalid argument
1+0 records in
0+0 records out
0 bytes transferred in 0.000 secs (0 bytes/sec)
$ doas disklabel -E cd0
cd0> a
partition: [a]
offset: [0]
size: [2236704]
FS type: [4.2BSD]
cd0> w
cd0> p
OpenBSD area: 0-2236704; size: 2236704; free: 0
# size offset fstype [fsize bsize cpg]
a: 2236704 0 4.2BSD 2048 16384 1
c: 2236704 0 unused
cd0> q
No label changes.
The same drive can be formatted and used on Mac OS X.
Thanks and best regards,
Siegfried
Did you try 2K blocks? The low level of CDROM only works that way.
Blocks larger than or equal to 2k get a "dd: /dev/rcd0c: short write on
character device”. Regarding to cd(4) I thought the device is readonly, so dd(1) and
disklabel(8) cannot write on it, but fdisk(8) works fine.
$ doas dd if=/dev/urandom of=/dev/rcd0c bs=2k
dd: /dev/rcd0c: short write on character device
dd: /dev/rcd0c: Invalid argument
1+0 records in
0+1 records out
512 bytes transferred in 0.008 secs (57960 bytes/sec)
$ doas dd if=/dev/urandom of=/dev/rcd0c bs=512
dd: /dev/rcd0c: Invalid argument
1+0 records in
0+0 records out
0 bytes transferred in 0.000 secs (0 bytes/sec)
/dev/cd0 is likely a symbolic link to something else in /dev.
It's not clear what's going on unless we know exactly what's being used.
"cd0" is not a usual OpenBSD device access even though one sees
that in dmesg.
OpenBSD disk-like devices are usually referenced in the very
old style which distinguishes "raw" [unbuffered direct to device]
from "cooked" [system buffered]. This differs from at least Linux practice.
Dunno about other BSDs or Macs.
Buffered devices are essentially only used to mount as filesystems.
A raw device is /dev/r<controller-or-generic-type><unit-number><partition>
A buffered device is
/dev/<controller-or-generic-type><unit-number><partition>
Note that there is always a partition letter.
The kernel will always emulate a 'c' partition = whole device if necessary.
So the most specific way to refer to your cd device is /dev/rcd0c.
As a convenience and to reduce operator errors, many system maintenance
programs will deduce /dev/r<specified-device>c from a bare device
like sd0. This can be confusing to people new to OpenBSD.
