Re: [Libcdio-devel] Distraction over Wikipedia topic, was Rock Ridge and libisofs/xorriso 'AL' extension

[Thomas Schmitt]

Hi,

Natalia Portillo wrote:
> The MODE SELECT is that basically you can change "sector size" on
> several SCSI devices.

Indeed ? Which Mode Page does this ?
I am looking at MMC-1 and MMC-5 and only see in Mode Page 0x05 the field
Data Block Type. It selects one of the various block write modes which
expect from the burn program to send 2048 to 2448 of the payload bytes
of a CD sector.
(Not applicable to DVD or BD media.)

SPC specs mention the command MODE SELECT but delegate the specification
of mode pages to the specialized device class documents. For optical drives
that would be MMC.


> I also have some Yamaha drives with that jumper.

My last Yamaha died in 2003. :(...

Methusalem on my desk is an LG Blu-ray burner of 2008.


> So there's the question, anything that emulates an ISO with those boot
> sectors, should suppor the "MODE SELECT" command somehow or expect the
> applications it is feeding to do the sector cutting.

Nowadays i expect block size 2048 with all optical media and am prepared
to convert adresses which are intended for 512 byte blocks before reading
blocks from optical media.
Vice versa, the 2048 byte block addresses need to be converted to the
block size of a 512 byte device, like a USB stick.

Within the ISO 9660 specs for optical media, i only know of the El Torito
boot image size field, which counts in 512 byte blocks.
All other filesystem and Boot Record aspects are for 2048 bytes.

In general, ISOs have emancipated themselves from CD-ROM.
They now live on DVD and BD (where the proprietary software community wanted
to enforce UDF), on USB sticks, and even in data files which get submitted
to virtual machines as virtual CD or hard disk.
So i would not assume that SCSI hardware commands are specially related to
interpreting the content of ISO 9660 filesystems.


Have a nice day :)

Thomas