RE: I request inclusion of SAS Transport Layer and AIC-94xx into the kernel

From: Andrew Patterson (andrew.patterson_at_hp.com)
Date: 09/30/05

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    To: "Salyzyn, Mark" <mark_salyzyn@adaptec.com>
Date:	Fri, 30 Sep 2005 12:39:54 -0600

    On Fri, 2005-09-30 at 13:07 -0400, Salyzyn, Mark wrote:
    > At the SAS BOF, I indicated that it would not be much trouble to
    > translate the CSMI handler in the aacraid driver to a similar sysfs
    > arrangement. If such info can be mined from a firmware based RAID card,
    > every driver should be able to do so. The spec writers really need to
    > consider rewriting SDI for sysfs (if they have not already) and move
    > away from an ABI.

    SDI is supposed to be a cross-platform spec, so mandating sysfs would
    not work. I suggested to the author to use a library like HPAAPI (used
    by Fibre channel), so you could hide OS implementation details. I am in
    fact working on such a beasty (http://libsdi.berlios.de). He thinks
    that library solutions tend to not work, because the library version is
    never in synch with the standard/LLDD's. Given Linux vendor lead-times,
    he does have a valid point.

    Note that a sysfs implementation has problems. Binary attributes are
    discouraged/not-allowed. There is no atomic request/response
    operations, buffers limited to page size, etc. Other alternatives are
    configfs, SG_IO, and the above mentioned character device. None are a
    complete replacement for the transactional nature of IOCTL's. A group
    of us are looking into this. We probably should be taking it to
    linux-scsi, but didn't want to get it caught up in the current flamewar.

    Andrew

    >
    > Sincerely -- Mark Salyzyn
    >
    > -----Original Message-----
    > From: Tuikov, Luben
    > Sent: Friday, September 30, 2005 12:47 PM
    > To: andrew.patterson@hp.com
    > Cc: dougg@torque.net; Linus Torvalds; Luben Tuikov; SCSI Mailing List;
    > Linux Kernel Mailing List
    > Subject: Re: I request inclusion of SAS Transport Layer and AIC-94xx
    > into the kernel
    >
    > On 09/30/05 12:26, Andrew Patterson wrote:
    > >
    > > I talked to one of the authors of these specs. SDI is an attempt to
    > > create an open standard for the somewhat proprietary CSMI spec
    > > developed by HP. It is currently languishing in t10 due to the IOCTL
    > > problem you describe below (the "no new IOCTL's" doctrine caught them
    > > by surprise). There is some thought to going to a write()/read() on a
    > > character device model, but this has various problems as well.
    >
    > I think that read/write from a char device is going away too.
    >
    > For this reason I showed the whole picture of the SAS
    > domain in sysfs _and_ created a binary file attr to send/receive SMP
    > requests/responses to control the domain and get attributes
    > ("smp_portal" binary attr of each expander).
    >
    > It is completely user space driven and a user space library
    > is simple to write.
    >
    > See drivers/scsi/sas/expander_conf.c which is a user
    > space utility. For the output see Announcement 3:
    > http://linux.adaptec.com/sas/Announce_2.txt or here:
    > http://marc.theaimsgroup.com/?l=linux-scsi&m=112629509318354&w=2
    >
    > The code which implements it is very tiny, at the bottom
    > of drivers/scsi/sas/sas_expander.c
    > -
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