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Subject: Platform device matching, & weird strncmp usage
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Greg KH <greg@kroah.com>
Cc: Linux Kernel list <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>
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Date: Fri, 06 Jan 2006 16:59:39 +1100
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Hi !

In 2.6.15, platform device matching works according to this comment in
the code, or rather are supposed to:


 *	Platform device IDs are assumed to be encoded like this:
 *	"<name><instance>", where <name> is a short description of the
 *	type of device, like "pci" or "floppy", and <instance> is the
 *	enumerated instance of the device, like '0' or '42'.

However, looking a few lines below, I see the actual implemetation:

static int platform_match(struct device * dev, struct device_driver * drv)
{
	struct platform_device *pdev = container_of(dev, struct platform_device, dev);

	return (strncmp(pdev->name, drv->name, BUS_ID_SIZE) == 0);
}

As far as I know, strncmp() is _NOT_ supposed to return 0 if one string
is shorter than the other and they match until that point. Thus the
above will never match unless the <name> portion of pdev->name is
exactly of size BUS_ID_SIZE which is obviously not the case...

Did I miss something or do we expect a "special" semantic for strncmp in
the kernel ?

Ben.


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