[PATCH 1/2] Initial support for Allwinner's Security ID fuses

Greg KH
2013-06-24T16:04:40Z

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