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    SubjectRe: [patch 4/6] ps3: Disk Storage Driver
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    On Fri, 2007-06-15 at 14:19 -0700, David Miller wrote:
    > From: Alan Cox <alan@lxorguk.ukuu.org.uk>
    > Date: Fri, 15 Jun 2007 17:15:45 +0100
    >
    > > > > Any particular reason why this is done as a separate block device driver
    > > > > rather than as SCSI?
    > > >
    > > > Because no new fake SCSI drivers are accepted anymore.
    > >
    > > Where did drivers/ata come from ;)
    > >
    > > How about making it a fake ata driver if James is being fussy 8)
    >
    > That sounds like a good idea for my virtual I/O case on
    > Niagara too actually :-)

    I have no objections to VIO servers speaking SCSI ... if you want to do
    that, I suggest you look at an existing example, like
    drivers/scsi/ibmvscsi (the actual communication piece is very ppc
    hypervisor specific, though).

    However, I do strongly believe that using SCSI for devices which truly
    aren't SCSI (i.e. you have to code a shim in the driver between the SCSI
    commands and whatever your device speaks) is wrong ... if SCSI has
    features that the generic block layer doesn't, then we need to move the
    function from SCSI to block to give you access ... in theory this was
    the rationale for having libata as the last "fake" SCSI driver, so we
    could identify this functionality and begin to move it.

    > Another quirk I have to deal with is that under LDOMs you
    > can export full disks and also just slices. So I'll have
    > to get down into the partition machinery to support that
    > somehow.

    For this, it sounds like you might find nbd a more enticing
    proposition ... it already is partition independent and is basically a
    block to net socket exporter.

    James


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