linux-kernel - Re: [PATCH 3/5] staging: vme: add functions for bridge module refcounting

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Message-ID: <4E4E21E6.3050400@ge.com>
Date:	Fri, 19 Aug 2011 09:42:14 +0100
From:	Martyn Welch <martyn.welch@...com>
To:	"Emilio G. Cota" <cota@...ap.org>
CC:	devel@...verdev.osuosl.org, Manohar Vanga <manohar.vanga@...n.ch>,
	gregkh@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] staging: vme: add functions for bridge	module	refcounting

On 19/08/11 09:32, Martyn Welch wrote:
> On 13/08/11 09:54, Emilio G. Cota wrote:
>> On Fri, Aug 12, 2011 at 12:30:49 +0200, Manohar Vanga wrote:
>>> This patch adds functions that allow for reference counting
>>> bridge modules. The patch introduces the functions
>>> 'vme_bridge_get()' and 'vme_bridge_put()'.
>> (snip)
>>> +int vme_bridge_get(unsigned int bus_id)
>> (snip)
>>> +void vme_bridge_put(struct vme_bridge *bridge)
>>
>> Note the input parameter imbalance; in fact this is serious
>> (see my email on patch 5) because _get() needs to acquire
>> vme_buses_lock, whereas _put() doesn't. Since a caller with
>> bridge has bridge->num, but the opposite doesn't hold (num
>> doesn't give you the bridge without acquiring vme_buses_lock),
>> it seems reasonable to me to take the bus_id as the input for
>> both functions, because the requirements on the caller are lower.
>>
> 
> Patch 4 makes changes the struct vme_bridge to struct vme_dev. Looking at the
> callers we are then effectively doing:
> 

Patch 5 even.

Martyn

> vme_bridge_get(vme_dev.id)
> 
> Then in vme_bridge_get(), looping through all the buses to find the one with
> the correct id...
> 
> We could just pass in the struct vme_dev to both functions.
> 
> Martyn
> 
>> But the locking needs to be handled with care, see my reply
>> to patch 5.
>>
>> 		Emilio
>>
>> _______________________________________________
>> devel mailing list
>> devel@...uxdriverproject.org
>> http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
> 
> 


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