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    SubjectRe: What still uses the block layer?
    On Sunday 14 October 2007 12:46:12 pm Stefan Richter wrote:
    > David Newall wrote:
    > > That is so rude.

    When a reply contains as a reply to the first paragraph "you're wrong" with no
    elaboration, and as a reply to the second paragraph nothing but expletives
    and personal insults, I tend to stop reading. It really doesn't come across
    as a serious reply.

    I was at least attempting to ask a serious question.

    > Such responses sometimes happen after provocative posts like the thread
    > starter's. He could have asked straight away for help with fixing his
    > boot environment instead of wrapping his question into a feigned design
    > discussion. It appeared as if he is out for a fight rather than
    > interested in help.

    Actually, I was going through Documentation/block thinking about making a
    00-INDEX for it, but my earlier questions of the scsi guys left me with the
    impression that the block layer is _not_ used by the SCSI layer. And since
    every non-embedded modern storage device I'm aware of has been consumed by
    the SCSI layer (despite none of them actually having a discernably closer
    relationship to SCSI than ATA did), I didn't know whether or not it was more
    appropriate to index this directory or request its deletion. So I asked.

    Back when I asked the scsi guys about this, I got no direct answer. I
    asked "where does the block layer work into this" in the context of questiosn
    about the relationship between the scsi upper, middle, and lower layers, and
    I never got a reply, even though the question was quoted back at me here:

    The closest I got to an answer was later in the thread:

    Which said:
    > That approach makes the Linux block layer either a nuisance,
    > irrelevant or a complete anachronism (in the case of OSD).
    > IMO the linux block layer should be morphed into a library
    > of internal queue handling routines. Storage upper level
    > drivers such as sd can continue to present the "block"
    > view ** of storage devices such as disks.

    The gist of the thread (and the documentation I was referred to) is that the
    scsi "upper layer" presents /dev nodes and ioctls, the scsi mid-layer is a
    routing layer very roughly analogus to a TCP/IP stack, and the scsi low-layer
    drivers interface with specific pieces of hardware. Apparently, the block
    layer is not between any of these, they talk directly to each other. This
    would seem to indicate that I/O requests made to scsi devices are never
    routed through a common block I/O request handling layer shared with non-SCSI
    block devices. I was not, however, certain of this, hence my attempt to
    bring the topic back up.

    Oh, and sending a patch correcting Jens Axboe's address in this old
    documentation. He's apparently at Oracle now...

    "One of my most productive days was throwing away 1000 lines of code."
    - Ken Thompson.
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