Re: SCSI over USB showstopper bug?

[Joerg Schilling]

Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:

> > > > it looks as if SG_GET_RESERVED_SIZE & SG_SET_RESERVED_SIZE
> > > > are not in interaction with the underlying SCSI transport.
> > > > 
> > > > Programs like readcd and cdda2wav that try to get very large SCSI
> > > > transfer buffers get a confirmation for nearly any SCSI transfer size 
> > > > but later when readcd/cdda2wav try to transfer data with an
> > > > actual SCSI command, they fail with ENOMEM.
> > > > 
> > > > Correct fix: let sg.c make a callback to the underlying SCSI transport
> > > > 		and let it get a confirmation tfor the buffer size.
> > > > 
> > > > Quick and dirty fix: reduce the maximum allowed DMA size to the smallest
> > > > 		max DMA size of all SCSI transports.
> > >
> > > real good fix:
> > >
> > > use SG_IO on the device directly that checks this already
> > 
> > From looking into the source, this claim seems to be wrong.
>
> The block layer SG_IO entry point does what Arjan describes - it checks
> the queue settings, which must match the hardware limits. It needs to,
> since it won't accept a command larger than what the path to that device
> will allow in one go. The SCSI sg variant may be more restricted, since
> it should handle partial completions of such commands.

Then someone should change the source to match this statements.

>From a report I have from the k3b Author, readcd and cdda2wav only work
if you add a "ts=128k" option. 

Jörg

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