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    SubjectRe: [PATCH] s390: Hypervisor File System
    Date
    On May 2, 2006, at 17:49:08, Kay Sievers wrote:
    > If you can assume that processes accessing the values are
    > cooperative, it already works without any changes:
    >
    > $ time flock /sys/class/firmware echo 1 > /sys/class/firmware/
    > timeout
    > real 0m0.005s
    >
    > $ flock /sys/class/firmware sleep 5&
    > [1] 6468
    >
    > $ time flock /sys/class/firmware echo 1 > /sys/class/firmware/
    > timeout
    > real 0m3.558s

    But that doesn't solve the problem for framebuffer devices or for the
    s390 code. Such transactions have one or more of the following
    properties:

    (1) A read operation is _expensive_ or adds unacceptable latencies
    and should be done as rarely as possible
    (2) The data must be all written to hardware simultaneously by the
    kernel; a partial update does not make sense and would cause
    undesired operation from the hardware.

    The idea with the transactions would be to create a kernel-memory
    buffer-layer of sorts on top of the underlying sysfs tree to cache
    the read data and collect writes for an atomic commit. I'll see if I
    can make something work.

    Cheers,
    Kyle Moffett
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