linux-kernel - Re: [PATCH 5/8] staging: vme: add functions for bridge module refcounting

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Date:	Tue, 9 Aug 2011 15:24:13 +0200
From:	Manohar Vanga <manohar.vanga@...n.ch>
To:	Martyn Welch <martyn.welch@...com>
CC:	"Emilio G. Cota" <cota@...ap.org>, <gregkh@...e.de>,
	<devel@...verdev.osuosl.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] staging: vme: add functions for bridge module
 refcounting

Hey Martyn,

> I think that by refcounting the resources being used we will know whether a
> bridge module is being used or not, thus whether it can be unloaded or not. By
> reference counting the use of resources we minimise the chance of poorly
> written drivers using resources, but not registering the fact that they are in
> fact using a VME bridge.

In the end, this discussion is about what we want the bride module reference count
to represent. I see your point here that it would be really useful to know what
resources have been allocated. I am just wondering whether the module refcount is
a good place to give information on allocated resources (rather than the bridge
module refcount).

I am not really an expert in these matters but would something like a sysfs file
be a cleaner approach to providing information on allocated resources within the
driver?

With this approach, I am also thinking about cases where resources are not allocated
within the probe call. This can cause issues if the bridge module is removed after
a successful probe but before the resources are allocated. This would be a direct
bug :-/

If we really don't want explicit module refcounting by drivers, can we perhaps use
the return value of the probe to automatically do this? eg. in vme_bus_probe() like
below:

    int ret = 0;
    ...
    vme_bridge_get(bridge);
    if (driver->probe)
            ret = driver->probe(vdev);
    if (ret)
        vme_bridge_put(bridge);
    return ret;

Just a thought. Feel free to shoot it down if you think it's the incorrect
approach :P

Thanks!

--
/manohar
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