x86/intel_rdt: Add mkdir to resctrl file system

Resource control groups are represented as directories in the resctrl
file system. The root directory describes the default resources available
to tasks that have not been assigned specific resources. Other directories
can be created at the root level to make new resource groups. It is not
permitted to make directories within other directories.

Hardware uses a CLOSID (Class of service ID) to determine which resource
limits are currently in effect. The exact number available is enumerated
by CPUID leaf 0x10, but on current implementations it is a small number.
We implement a simple bitmask allocator for CLOSIDs.

Each resource control group uses one CLOSID, which limits the total number
of directories that can be created.

Resource groups can be removed using rmdir.

Signed-off-by: Fenghua Yu <[email protected]>
Cc: "Ravi V Shankar" <[email protected]>
Cc: "Tony Luck" <[email protected]>
Cc: "Shaohua Li" <[email protected]>
Cc: "Sai Prakhya" <[email protected]>
Cc: "Peter Zijlstra" <[email protected]>
Cc: "Stephane Eranian" <[email protected]>
Cc: "Dave Hansen" <[email protected]>
Cc: "David Carrillo-Cisneros" <[email protected]>
Cc: "Nilay Vaish" <[email protected]>
Cc: "Vikas Shivappa" <[email protected]>
Cc: "Ingo Molnar" <[email protected]>
Cc: "Borislav Petkov" <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

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