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Date: Tue, 08 Apr 2003 00:39:46 -0400
From: Jeff Garzik <jgarzik@pobox.com>
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To: Rusty Russell <rusty@rustcorp.com.au>
CC: Zwane Mwaikambo <zwane@linuxpower.ca>, linux-kernel@vger.kernel.org,
       hch@infradead.org
Subject: Re: SET_MODULE_OWNER?
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Rusty Russell wrote:
> In message <Pine.LNX.4.50.0304072212310.21025-100000@montezuma.mastecende.com> 
> you write:
> 
>>(e.g. pci-dma api changes). Regardless, here is a typical use in a 
>>netdriver.
>>
>>	/* dev and dev->priv zeroed in alloc_etherdev */
>>	dev = alloc_etherdev (sizeof (*tp));
>>	if (dev == NULL) {
>>		printk (KERN_ERR PFX "%s: Unable to alloc new net device\n", pd
> 
> ev->slot_name);
> 
>>		return -ENOMEM;
>>	}
>>	SET_MODULE_OWNER(dev);
>>	tp = dev->priv;
>>	
>>	/* followed by ... */
>>	dev->foo = __foo;
>>	dev->bar = __bar;
> 
> 
> I don't understand how that helps compatibility over:
> 
> 	dev->owner = THIS_MODULE;
> 
> Both will:
> 1) Work on 2.4 and 2.5
> 2) Break on 2.2.


Wrong.

SET_MODULE_OWNER works in 2.2 _and earlier_... given some compat glue in 
a "#include <kcompat>" macros.

You may take a look at "kcompat" for further examples. 
http://sf.net/projects/gkernel/   I provide an example of how to get a 
net driver from 2.4 running under 2.2, such that the 2.4 driver 
-appears- to be completely free of compatibility glue.

The only sticking points in such glue are when structure members are 
directly exposed in the source code.  That cannot be worked around with 
cpp magic.  This is why SET_MODULE_OWNER exists, this is why 
pci_{get,set}_drvdata() exist, and so on.

	Jeff