rubix.md

Ruben's Kernel (Rubix?)

A very simple kernel, with priority based scheduling and a file system.

Features

• SYS Calls
  • yield - ends the current time slice.
  • write - writes to an open file descriptor.
  • read - reads from an file descriptor. Returns length of read, 0 on EOF. May blocking - see set_nonblocking.
  • close - closes a file descriptor.
  • dup2 - duplicates fd from old to new. new is closed if it already exists.
  • pipe - creates a pipe. fd[0] is read, fd[1] is write.
  • fopen - open file. Not quite POSIX, as it's non-blocking
  • fork - clones process. Return value is 0 if child, PID of child if parent, -1 if error.
  • exec - replaces the process with another program. PID is kept. Stack and FDs (except in/out/err) are destroyed.
  • exit - exits with exit code.
  • wait - waits for a child program to exit, and gives exit code.
  • kill - sends a kill signal to a process. Killed processes will not return an exit code. signal is not yet implemented.
  • setpriority - set priority of child process.
  • set_nonblocking - is not POSIX, unfortunately. Set pipe non-blocking.
• LibC help functions
  • popen - opens a process and returns a FD. Uses fork, pipe, exec, and dup2.
  • wait/waitpid - both use the wait syscall.
• Processe
  • time slicing - timer based timer slices.
  • priority-based - priority(P) = priority_base(P) + slices_since_last_ran(P)
  • blocked queue - for processes waiting for a process or file resource.
  • process ownership - processes have a parent, which can kill/wait them.
  • process groups - a limited type of process group, where all processes that share a parent and the parent itself are in a group.
• Files
  • FiDes - File descriptor. Interacted with using function pointers. Can be blocking or not.
  • pipe - Pointed to by a FD.
  • in/out/err - these are "files" too!
  • filesystem - Files are limited to 256 bytes, maximum of 10 files.

References

All references access March 2017.

Online

• Linux Man-pages. Various. man7.org
• Wait sys call. The Open Group. pubs.opengroup.org
• Exit sys call. The Open Group. pubs.opengroup.org
• POSIX IPC. Oracle. docs.oracle.com
• Linux Interprocess Communications. Goldt. S, Van der Meer. S, Welsh. M. tldp.org
• Interprocess Communication (IPC), Pipes. Marshall, D. Users.cs.cf.ac.uk
• General overview of the Linux file system. Machtelt. G. tldp.org

Print

• Cormen. T, Leiserson. C, Rivest. R, Stein. C. Introduction to Algorithms 3rd Edition, (Massachusetts Institute of Technology, 2009) Heapsort and Priority Queues. pp151-166