Re: unloading drivers and usage counters

[David Hinds <dhinds@sonic.net>]

On Sun, Jan 21, 2001 at 09:28:41PM -0800, David Brownell wrote:

> Sounds like a substantial change in the model for what module use
> counts should be.  Maybe the pcmcia_cs tools have a better model?

For PCMCIA, module use counts are incremented when a device is opened,
and decremented when closed, just like most non-hot-plug modules.
Attaching a driver to a newly hot plugged device does not increment
its use count.

To decide when to unload a module, the cardmgr daemon keeps track of
the number of times a module has been requested in response to new
device insertions; this count can indeed get messed up if people
manually unload modules, or if cardmgr is killed and restarted.  I am
not bothered much by this, because the consequences are mostly
harmless and the user has to go out of their way to mess up the
automatic usage counting.  In practice, no one has ever complained to
me about it.

The PCMCIA subsystem does provide /proc/bus/pccard/drivers, which
lists what drivers are present, which are modules vs. which are static
linked, and the actual number of present devices that are associated
with each driver.  Cardmgr currently only uses the module/static flag
from this file, so that it won't bother trying to remove a static
driver; it would not be much work to also use the usage information
for precise decisions about when to unload modules.

-- Dave

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