linux-kernel - Re: [PATCH 1/2] misc: add CARMA DATA-FPGA Access Driver

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Message-ID: <20110209234231.GA5707@core.coreip.homeip.net>
Date:	Wed, 9 Feb 2011 15:42:31 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"Ira W. Snyder" <iws@...o.caltech.edu>
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] misc: add CARMA DATA-FPGA Access Driver

On Wed, Feb 09, 2011 at 03:35:45PM -0800, Ira W. Snyder wrote:
> On Wed, Feb 09, 2011 at 10:27:40AM -0800, Dmitry Torokhov wrote:
> 
> [ snip stuff I've already fixed in the next version ]
> 
> > > 
> > > The requirement is that the device stay open during reconfiguration.
> > > This provides for that. Readers just block for as long as the device is
> > > not producing data.
> > 
> > OK, you still need to make sure you do not touch free/used buffer while
> > device is disabled. Also, you need to kick readers if you unbind the
> > driver, so maybe a new flag priv->exists should be introduced and
> > checked.
> > 
> 
> I don't understand what you mean by "kick readers if you unbind the
> driver". The kernel automatically increases the refcount on a module
> when a process is using the module. This shows up in the "Used by"
> column of lsmod's output.
> 
> The kernel will not let you rmmod a module with a non-zero refcount. You
> cannot get into the situation where you have rmmod'ed the module and a
> reader is still blocking in read()/poll().

However you can still unbind the driver from the device by writing into
driver's sysfs 'unbind' attribute.

See drivers/base/bus.c::driver_unbind().

Thanks.

-- 
Dmitry
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