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    SubjectRe: ide filters / 'ide dump' / 'bio dump'


    On Wed, 13 Mar 2002, Jeff Garzik wrote:
    > bert hubert wrote:
    >
    > ># biodump /dev/hda
    > >09:09:33.023 READ block 12345 [10 blocks]
    > >09:09:33.024 READ block 12355 [10 blocks]
    > >09:09:33.025 READ block 12365 [10 blocks]
    > >09:09:34.000 WRITE block 12345 [1 block]
    >
    > Definitely an interesting idea... With this new stuff Linus talked
    > about in his proposal and what I'm thinking about, it shouldn't be too
    > hard to do.

    Note that I actually think we're talking about two different things.

    There's the notion of _feeding_ special requests onto the request queue
    through some interface that also can refuse to feed certain kinds of
    requests. That is needed for the special commands, and is "above" the
    requests queue layer.

    That interface doesn't really support filtering of requests that other
    people (notably the regular kernel itself) is also feeding to the request
    queue.

    Note that one of the big issues with the request queue is that it acts as
    a funnel: it (very much by design) can, and does, take requests from
    different places, and nobody needs to "own" the request queue. But the
    kind of "feed this raw request down" module that has been talked about
    would have absolutely _zero_ visibility into what others are feeding into
    the request queue.

    If you actually want to filter other peoples requests, then you have to do
    something completely different, namely set up a request queue of your own,
    then exporting _your_ request queue as the request queue for <major,minor>
    and then taking the requests off that queue internally, and moving them to
    the original queue after you've done filtering.

    Basically a simplified "loopback" thing that doesn't even need to do any
    remapping.

    The two are totally independent, they work on requests queues at different
    levels (one feeds some random request queue, the other changes how we look
    up a request queue and inserts its own queue in between).

    Linus

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