[openib-general] Location for iser-target code

[Dan Bar Dov]

On 4/10/06, Mike Christie <michaelc at cs.wisc.edu> wrote:
> Dan Bar Dov wrote:
> > On 4/10/06, FUJITA Tomonori <fujita.tomonori at lab.ntt.co.jp> wrote:
> >> The OLS abstract may be more informative.
> >>
> >> http://www.linuxsymposium.org/2006/view_abstract.php?content_key=19
> >
> > Is the full document available as well?
>
> The code is shorter than the paper.
>
> >
> >> In short, tgt is the framework for SCSI target drivers. The
> >> combination of tgt and the iSCSI target driver for NIC provides the
> >> similar features that IET does.
> >
> > SCSI targets are LLDs that sit below the mid-layer. iSCSI target on
> > the other hand is a "network" protocol driver, that sits above SCSI
> > (sd, st, sg, or directly over mid-layer). Seems like you'd need two
> > different frameworks, no?
> >
>
> tgt/stgt is probably two frameworks from your point of view. There is a
> kernel part for target LLDs to hook into. The kernel part is similar to
> scsi-ml, actually it builds onto it and uses some of the scsi-ml
> functions, and provides code to share for tasks like creating scatter
> lists and mapping commands between the kernel and userspace. The target
> LLD basically handles lower level issues like DMAing the data, transport
> issues, etc, pretty much what a scsi-ml initiator driver does. For

What do you mean by scsi-ml initiator?

> iscsi, the tgt lld performs similar tasks as the initiator. It parses
> the iscsi PDUs or puts them on the interconnect, handles session and
> connection manamgement (this would be done like open-iscsi though), but
> then then passes the scsi command to tgt's kernel code.
>
> The other part of the framework is the userspace component. The tgt
> kernel component basically passes scsi commands and task management
> functions to a userspace daemon. The daemon contains the scsi state
> machine and execute the IO. When it is done it informs the the kernel
> component which in turn maps the data into the kernel, forms scatter
> lists, and then passes them to the target LLD to send out.
>
I got completely confused. I understand (obviously wrongly) that to implement an
iscsi target (or srp target for that matter), I would write the
network facing part in kernel,
that would pass the tasks and data to the user mode, the user mode will perform
the tasks using scsi drivers (sd/st/sg), and once completed report
back to the network facing part.

I guess I'd need a diagram or two to understand :-)

Dan