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

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Message-ID: <20110209233544.GA5303@ovro.caltech.edu>
Date:	Wed, 9 Feb 2011 15:35:45 -0800
From:	"Ira W. Snyder" <iws@...o.caltech.edu>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
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 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().

Thanks for the review. A v6 is coming right up.

Ira
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