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

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jun 24, 2013 at 07:11:35PM +0200, Oliver Schinagl wrote:
> Hey Greg,
> On 06/24/13 18:04, Greg KH wrote:
> >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.
> Since Maxime kinda asked for me, I hope you don't mind me following up.
> 
> That doc doesn't mention the binary interface at all. Initially I
> had both devices up, the 'read' device as a textual representation
> and added the binary one later. Maxime and I decided the binary one
> made more sense, as the only textual user would be a human and they
> don't poke that entry that often.
> 
> So what default way exists for binary files or how would that be solved?

The same interface should work just fine for binary files, have you
tried it?

thanks,

greg k-h