[$] Fixing getrandom()

A report ofa boot hang in the 5.3 series has led to an enormous, somewhat contentiousthread on the linux-kernel mailing list. The proximate cause was some changes that made theext4 filesystem do less I/O early in the boot phase, incidentally causingfewer interrupts, but the underlying issue was the getrandom()system call, which was blocking until the /dev/urandom poolwas initialized-as designed. Since the system in question was notgathering enough entropy due to the lack of unpredictable interrupttimings, that would hang more or less forever. That has called intoquestion the design and implementation of getrandom().