There is also another behavior, which is used by usb-storage.
Drivers for SCSI host adaptor cards generally allow their usage count to
be managed by the SCSI layer. This allows high-level information (i.e.
what devices are actually in use) to affect the usage count for a driver
which doesn't really have an 'open' semantic.
Matt Dharm
On Wed, 5 Apr 2000, Donald Becker wrote:
> On Wed, 5 Apr 2000, Alessandro Rubini wrote:
>
> > I'm currently studying the USB kernel subsystem using modules, and I
> > noticed how the usage count of specific device never raises above
> > zero. Should that be construed as a feature?
> >
> > I'd personally prefer to have the driver marked as busy when there is
> > a device using it. For example, a devault crontab in Debian removes
> ..
> > The best option would be to increment the count when the device is
> > actually being read, but the current layout of the USB and input
> > subsystems make it impractical to do so, and I wouldn't like such
> > feature to be implemented as things are clean enough as they are now.
>
> My USB modules have varying semantics:
>
> Network drivers only have a non-zero usage count when they are up. They
> shut down the interface automatically on hardware disconnect.
>
> Character/block drivers only have a non-zero usage count when they are
> open. Removing the device does not (can not) automatically close, so the
> module is not removed until the last opener finishes.
>
> Mouse and keyboard device drivers have a non-zero usage count whenever
> they are plugged in. Any explicit mouse open further increments the usage
> count. Keyboards just inject events, and thus they never know if anyone
> is listening.
>
> I believe this is close to the semantics of most of the pre-2.4 drivers, but
> I'm not certain that it's consistent or documented.
>
> Donald Becker
> Scyld Computing Corporation, [EMAIL PROTECTED]
>
>
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