On Mon, Jun 24, 2013 at 11:21:16PM +0200, Oliver Schinagl wrote: > On 06/24/13 20:15, Greg KH wrote: > >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? > I'll just take the plunge and make myself look stupid ;) > > I tried to change things around, used DEVICE_ATTR(eeprom, S_IRUGO, > sid_read, NULL); So far so good I'd hope.
Ick, no. > Of course now I'll have to change the function's parameters from > > static ssize_t sid_read(struct file *fd, struct kobject *kobj, > struct bin_attribute *attr, char *buf, > loff_t pos, size_t size) > > to > > static ssize_t sid_read(struct device *dev, > struct device_attribute *attr, char *buf) Which is what do you do not want, as you find out: > But now, I'm missing things like 'pos' and 'size', both which > determine the requested bytes. True, in this specific driver we are > talking about 'only' 16 bytes, but what if it weren't but a few MiB > and in sysfs we want to read some random byte, will we have to put > the entire blok into the buffer? > > So sorry for not understanding, but ... I don't understand :) Stick with a binary attribute, and attach that to the proper class structure and all should be fine. Ah crap, you're using a platform device. {sigh} Why? Why not use a "real" device which has a "real" class, and then use the interfaces there? greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/