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    Subject/proc format (was Device Registry (DevReg) Patch 0.2.0)
    On Wednesday 25 April 2001 19:10, you wrote:
    > The command
    > more foo/* foo/*/*
    > will display the values in the foo subtree nicely, I think.

    Unfortunately it displays only the values. Dumping numbers and strings
    without knowing their meaning (and probably not even the order) is not very

    > Better to factor the XML part out to a userspace library...

    But the one-value per file approach is MORE work. It would be less work to
    create XML and factor out the directory structure in user-space :)
    Devreg collects its data from the drivers, each driver should contribute the
    information that it can provide about the device.
    Printing a few values in XML format using the functions from xmlprocfs is as
    easy as writing
    proc_printf(fragment, "<usb:topology port=\"%d\" portnum=\"%d\"/>\n",
    get_portnum(usbdev), usbdev->maxchild);

    Extending the devreg output with driver-specific data means registering a
    callback function that prints the driver's data. The driver should use its
    own XML namespace, so whatever the driver adds will not break any
    (well-written) user-space applications. The data is created on-demand, so the
    values can be dynamic and do not waste any space when devreg is not used.

    The code is easy to read and not larger than a solution that creates static
    /proc entries, and holding the data completely static would take much more
    memory. And it takes less code than a solution that would create the values
    in /proc dynamically because this would mean one callback per file or a
    complicated way to specify several values with a single callback.


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