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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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