diff options
author | Grant Likely <grant.likely@secretlab.ca> | 2009-03-06 14:05:39 -0700 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2009-06-15 21:30:23 -0700 |
commit | b22813b373749d0878e7140e9a6eadf182298709 (patch) | |
tree | 835af1d5dc204db9c36514cb21000b32abea27d4 /Documentation/driver-model | |
parent | 3959214f971417f4162926ac52ad4cd042958caa (diff) | |
download | kernel_samsung_smdk4412-b22813b373749d0878e7140e9a6eadf182298709.zip kernel_samsung_smdk4412-b22813b373749d0878e7140e9a6eadf182298709.tar.gz kernel_samsung_smdk4412-b22813b373749d0878e7140e9a6eadf182298709.tar.bz2 |
Driver Core: Warn driver authors about adding device attributes
Add a blurb to the driver-model documentation about how (not) to add
extra attributes to a struct device at driver probe time.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation/driver-model')
-rw-r--r-- | Documentation/driver-model/device.txt | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/Documentation/driver-model/device.txt b/Documentation/driver-model/device.txt index a7cbfff..a124f31 100644 --- a/Documentation/driver-model/device.txt +++ b/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"); |