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SubjectRe: /proc format (was Device Registry (DevReg) Patch 0.2.0)
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>
> 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
> useful.
>
> > 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.

Personally, I think

proc_printf(fragment, "%d %d",get_portnum(usbdev), usbdev->maxchild);

(or the string "dddd ddd" with d representing a digit)
is shorter (and faster) to parse with

fscanf(input,"%d %d",&usbdev,&maxchild);

Than it would be to try parsing

<usb:topology port="ddddd" portnum="dddd">
with an XML parser.

Sorry - XML is good for some things. It is not designed to be a
interface language between a kernel and user space.

I am NOT in favor of "one file per value", but structured data needs
to be written in a reasonable, concise manner. XML is intended for
communication between disparate systems in an exreemly precise manner
to allow some self documentation to be included when the communication
fails.

Even Lisp S expressions are easier :-)

-------------------------------------------------------------------------
Jesse I Pollard, II
Email: pollard@navo.hpc.mil
Any opinions expressed are solely my own.
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