Re: Write to DVD-RAM

On Jul 25, 2019, at 10:24 PM, gwes <gwes@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)