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SubjectRe: Linux as a SCSI _Target_ device?

Hi Jeff,

On Thu, 12 Nov 1998, Jeff Noxon wrote:

> On Fri, Nov 13, 1998 at 12:30:23AM +0100, Gerard Roudier wrote:
> > Agreed, and you have the advantage not to have to cope with complex
> > context saving since the target interrupts transfers at its convenience.
> >
> > Indeed, there is no problem for implementing SCSI target mode with
> > NCR/SYMBIOS/LSI 53c[7-8]xx chips, but Linux does not provide kernel
> > interface for SCSI target mode.
>
> I may ultimately eat my words, but I'd like to try to do it.

YES!
I read you have been told about some SCSI project for Linux that
implements SCSI target mode. It seems guys wanted to implement kind of
network or cluster link. For that, just implementing the PROCESSOR device
should have been enough. You should have a look at this code, I think.

> I want to try to write a module that can export any Linux block device
> as a SCSI target emulating a direct-access device. I have a spare Alpha
> machine with an onboard 53c810 for the development.

You probably need at least a second controller for testing.

> I called Symbios/LSI this morning and they no longer have programming
> documentation for the 53c8xx. Apparently the merger has been a mess.

Perhaps somebody in the USA (is it your planet? :-)) can send you a copy
of such a manual. No need to have something recent. Seems the SYMBIOS
assembler program for DOS is available at their ftp site (in some tools
directory). The SYMBIOS site will be moved to LSI one at the end of this
year.

> They sent me a 53c8xx data book. Is the SCRIPTS programming info
> in there?

Data manuals have everythings needed to write your driver but lack of the
full SCRIPTS symbolic language syntax documentation. The ncr53c8xx driver
does not use the SYMBIOS SCRIPTS language but just some tricky C macros
for SCRIPTS programming, but Drew Eckward had written years ago a SCRIPTS
assembler in perl for his 53c7,8xx driver development. You should ask Drew
for his perl program, or perhaps the source is still available at some ftp
site.

> One of the list subscribers pointed me to an area on the Symbios FTP site
> (thanks!), and I've downloaded a lot of DOS code for implementing a RAM
> disk on the 53c8xx. I'm sure that will prove very useful. Now I need
> to acquaint myself with the Linux kernel guts. I used to love writing
> device drivers, but computers and OS's used to be a lot simpler. :)

SYMBIOS sample code are very interesting for target mode and may be
helpful for your project.

> Gerard, I'm hoping you can hold my hand on this one. :-)

Indeed, I will help you each time I will be able to.
But, for now, my advice is to study the SYMBIOS data manual and the SPI-2,
SPC and SBC t10 specifications. You can download the t10 specs from
something like:

ftp://ftp.symbios.com/pub/standards/t10/drafts/
(A README file is available in this directory)

> Alan Cox has pointed me to some resources to get familiar with Linux
> guts.

I just forgot you have to get familiar with these ones too. :-)

Regards,
Gerard.


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