[$] New system calls: pidfd_open() and close_range()

The linux-kernel mailing list has recently seen more than the usual amountof traffic proposing new system calls. LWN is endeavoring to catch up withthat stream, starting with a couple of proposals for the management of filedescriptors. pidfd_open() is a new way to create a "pidfd" filedescriptor that refers to a process in the system, whileclose_range() is an efficient way to close many open descriptorswith a single call.