Re: [Bug 7026] CD/DVD burning with USB writer doesn't work

[Douglas Gilbert <dougg@torque.net>]

James Bottomley wrote:
> On Wed, 2006-12-06 at 00:14 +0100, Joerg Schilling wrote:
>> Well, accept the patch if it works.
> 
> It's not about work/not work: it's about correctness.
> 
>>  And in case that you don't like it, make sure that the _parameter_ is
>> moved to where it belongs: to the low level transport layer.
> 
> It's not a low level property; it's a property of the generic queue,
> namely the maximum request size.  It exists for devices independent of
> SCSI (i.e. you'll want it for IDE and weirder transport attachment CDs
> as well).

Too much smoke and mirrors.

That maximum request size comes from the transport ** and
in many cases is a kludge between maximum, optimal and
defensive. The block paradigm is wrong for a pass through
because it requests transports to guess a "maximum",
trying to head off errors that the block layer isn't
particularly well equipped to handle at run time.

On the other hand a pass through gets layered error reporting.
So if a host (and/or its LLD driver) doesn't like the
size (or shape) of data to be sent/received with a
command, then it can say so (and I don't mean EIO or
ENOMEM). That leaves the ball in the court of the pass
through user. Perhaps in this case sysfs could be
useful. The problem may be transient.


** as always the OS could have run out of resources (e.g. ram)
   but again that is most likely transient.

Doug Gilbert