linux-kernel - Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

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Date:	Mon, 24 Jun 2013 09:04:40 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Oliver Schinagl <oliver+list@...inagl.nl>, arnd@...db.de,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	andy.shevchenko@...il.com, linux@....linux.org.uk,
	linus.walleij@...aro.org, linux-sunxi@...glegroups.com,
	Oliver Schinagl <oliver@...inagl.nl>
Subject: Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

On Mon, Jun 24, 2013 at 11:29:42AM +0200, Maxime Ripard wrote:
> Hi Greg,
> 
> On Mon, Jun 17, 2013 at 03:58:47PM -0700, Greg KH wrote:
> > On Mon, Jun 17, 2013 at 10:59:37PM +0200, Oliver Schinagl wrote:
> 
> [..]
> 
> > > +static int __init sunxi_sid_probe(struct platform_device *pdev)
> > > +{
> > > +	u8 entropy[SID_SIZE];
> > > +	unsigned int i;
> > > +	struct resource *res;
> > > +	void __iomem *sid_reg_base;
> > > +	int ret;
> > > +
> > > +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > > +	sid_reg_base = devm_ioremap_resource(&pdev->dev, res);
> > > +	if (IS_ERR(sid_reg_base))
> > > +		return PTR_ERR(sid_reg_base);
> > > +	platform_set_drvdata(pdev, sid_reg_base);
> > > +
> > > +	ret = device_create_bin_file(&pdev->dev, &sid_bin_attr);
> > > +	if (ret)
> > > +		return ret;
> > 
> > You just raced with userspace, having the file show up after the device
> > was announced to users that it was there.  Please use the proper device
> > file api to add default attributes to prevent this from happening.
> 
> Sorry if the question looks dumb, but what kind of race can we generate
> here?

Userspace gets told about the device from the driver core, udev runs and
reads all of the attributes, then your probe function comes along and
adds a new attribute.  Userspace will then not know about it at all.

> The device_create_bin_file is the last call that we make (if we except
> the entropy stuff, but it doesn't really matter here), so after we
> created the file, we have everything properly initialised so that our
> functions can be called, right?
> 
> And another dumb question for you, what is the "proper device file API"
> you are referring to ? :)

Please read Documentation/driver_model/device.txt and see the section on
Attributes for what to do.  If you have specific questions after reading
that, please let me know.

thanks,

greg k-h
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