Linux user space stack
 

Can any one brief me how linux user space stack is organsied and who manges its operations.

User space processes are children of init, which is started by the kernel upon boot. They interface with the kernel by means of system calls, file I/O, ioctls, and other mechanisms. The processes are managed by the process scheduler. There activities are fenced by a number of protection mechanisms offered in the system calls.

^^ About a year of a computer science degreee compressed into a paragraph

Unless, are you referring to things like spidev, or uinput -- User space interfaces for kernel subsystems? In this case, the magic is mostly just in exposing the right things in /dev and /sys, for direct manipulation via file descriptor, from userspace.