From eb7c04fa2d4820ab51c4cd03f6c917485a4c8584 Mon Sep 17 00:00:00 2001 From: Grant Likely Date: Fri, 6 Mar 2009 14:05:39 -0700 Subject: [PATCH] --- yaml --- r: 151233 b: refs/heads/master c: b22813b373749d0878e7140e9a6eadf182298709 h: refs/heads/master i: 151231: 644530c13e3dac4f675f9bc78799ab4b2d7cad12 v: v3 --- [refs] | 2 +- trunk/Documentation/driver-model/device.txt | 32 +++++++++++++++++++++ 2 files changed, 33 insertions(+), 1 deletion(-) diff --git a/[refs] b/[refs] index 35e8cb8b4730..5ee52b75fd34 100644 --- a/[refs] +++ b/[refs] @@ -1,2 +1,2 @@ --- -refs/heads/master: 3959214f971417f4162926ac52ad4cd042958caa +refs/heads/master: b22813b373749d0878e7140e9a6eadf182298709 diff --git a/trunk/Documentation/driver-model/device.txt b/trunk/Documentation/driver-model/device.txt index a7cbfff40d07..a124f3126b0d 100644 --- a/trunk/Documentation/driver-model/device.txt +++ b/trunk/Documentation/driver-model/device.txt @@ -162,3 +162,35 @@ device_remove_file(dev,&dev_attr_power); The file name will be 'power' with a mode of 0644 (-rw-r--r--). +Word of warning: While the kernel allows device_create_file() and +device_remove_file() to be called on a device at any time, userspace has +strict expectations on when attributes get created. When a new device is +registered in the kernel, a uevent is generated to notify userspace (like +udev) that a new device is available. If attributes are added after the +device is registered, then userspace won't get notified and userspace will +not know about the new attributes. + +This is important for device driver that need to publish additional +attributes for a device at driver probe time. If the device driver simply +calls device_create_file() on the device structure passed to it, then +userspace will never be notified of the new attributes. Instead, it should +probably use class_create() and class->dev_attrs to set up a list of +desired attributes in the modules_init function, and then in the .probe() +hook, and then use device_create() to create a new device as a child +of the probed device. The new device will generate a new uevent and +properly advertise the new attributes to userspace. + +For example, if a driver wanted to add the following attributes: +struct device_attribute mydriver_attribs[] = { + __ATTR(port_count, 0444, port_count_show), + __ATTR(serial_number, 0444, serial_number_show), + NULL +}; + +Then in the module init function is would do: + mydriver_class = class_create(THIS_MODULE, "my_attrs"); + mydriver_class.dev_attr = mydriver_attribs; + +And assuming 'dev' is the struct device passed into the probe hook, the driver +probe function would do something like: + create_device(&mydriver_class, dev, chrdev, &private_data, "my_name");