Re: trixie: cdrecord can no longer write to CD
Hi,
on the risk to become off topic (i watch out for interventions):
I wrote:
> > i found the new SCSI command whitelist of Linux in
> > https://sources.debian.org/src/linux/6.17.8-1/drivers/scsi/scsi_ioctl.c?hl=301#L267
Bigsy Bohr wrote:
> Isn't that a boolean whitelist?
Yes. The answer for w-needing commands depends on the value of the
parameter "open_for_write". Other listed commands need only the proven
ability to open the device file.
The answer "true" obviously means to allow the command, "false"
indicates rejection.
> I've read that MMC devices require additional MMC specific commands that
> are not whitelisted
MMC is nothing unusual but just the specific part of SCSI specs which
rules the operation of optical drives.
As said, the whitelist decisions of Linux about MMC commands look
reasonable and not like freshly changed.
IIRC SCSI-3 was split into multiple parts, among them the Primary
Commands (SPC) and the Multi Media Commands ("MMC"), a name from the
time of the "Multi Media Workstation", a PC with a CD-ROM drive and
speakers which could show images and post-stamp-sized videos.
The full list of contemporay parts is given by the skewed "D Z T ... F"
headline block in
https://www.t10.org/lists/op-num.htm
The columns with the marking letters tell which command occurs in which
part. E.g. TEST UNIT READY applies to all parts. REWIND only to SSC,
which i assume covers tape drives.
Most MMC commands are marked "optional", because the mandatory ones can
tell whether the others are supported by the drive with the loaded
medium type and tape.
> wodim's raw SCSI commands as opposed
> to cdrskin/libburn's block device packet writing).
Burning CD is done by official SCSI commands.
Some drives know vendor specific commands for which there is a reserved
command code number range in SCSI. Mostly for fancy features or for
firmware updates. libburn refrains from using them.
About "packet writing":
Both, wodim and libburn use on Linux the ioctl(SG_IO) for command
transfer.
https://tldp.org/HOWTO/SCSI-Generic-HOWTO
Once the now deprecated ioctl(CDROM_SEND_PACKET) was used by growisofs
for the same purpose
https://www.kernel.org/doc/html/latest/userspace-api/ioctl/cdrom.html
But i guess that the meme "packet writing" comes from the write type
"Packet/Incremental" for CD and DVD-R, a neighbor of "Track at Once",
"Session at Once", and "RAW". The write type is chosen by sending the
drive a "Write Mode Page" data chunk, which tells the desired
properties of the CD burn session.
On most DVD and all BD media types there are no such shenanigans.
Have a nice day :)
Thomas
Reply to: