It's important for the driver to provide a R/W ioctl to ensure that
two competing userspace processes don't race to provide or read each
others data.
This userspace character device will be used to perform SMBIOS calls
from any applications.
It provides an ioctl that will allow passing the WMI calling
interface buffer between userspace and kernel space.
This character device is intended to deprecate the dcdbas kernel module
and the interface that it provides to userspace.
To perform an SMBIOS IOCTL call using the character device userspace will
perform a read() on the the character device. The WMI bus will provide
a u64 variable containing the necessary size of the IOCTL buffer.
The API for interacting with this interface is defined in documentation
as well as the WMI uapi header provides the format of the structures.
Not all userspace requests will be accepted. The dell-smbios filtering
functionality will be used to prevent access to certain tokens and calls.
All whitelisted commands and tokens are now shared out to userspace so
applications don't need to define them in their own headers.
Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-by: Edward O'Callaghan <quasisec@google.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
For WMI operations that are only Set or Query readable and writable sysfs
attributes created by WMI vendor drivers or the bus driver makes sense.
For other WMI operations that are run on Method, there needs to be a
way to guarantee to userspace that the results from the method call
belong to the data request to the method call. Sysfs attributes don't
work well in this scenario because two userspace processes may be
competing at reading/writing an attribute and step on each other's
data.
When a WMI vendor driver declares a callback method in the wmi_driver
the WMI bus driver will create a character device that maps to that
function. This callback method will be responsible for filtering
invalid requests and performing the actual call.
That character device will correspond to this path:
/dev/wmi/$driver
Performing read() on this character device will provide the size
of the buffer that the character device needs to perform calls.
This buffer size can be set by vendor drivers through a new symbol
or when MOF parsing is available by the MOF.
Performing ioctl() on this character device will be interpretd
by the WMI bus driver. It will perform sanity tests for size of
data, test them for a valid instance, copy the data from userspace
and pass iton to the vendor driver to further process and run.
This creates an implicit policy that each driver will only be allowed
a single character device. If a module matches multiple GUID's,
the wmi_devices will need to be all handled by the same wmi_driver.
The WMI vendor drivers will be responsible for managing inappropriate
access to this character device and proper locking on data used by
it.
When a WMI vendor driver is unloaded the WMI bus driver will clean
up the character device and any memory allocated for the call.
Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-by: Edward O'Callaghan <quasisec@google.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
