Minix kernel, services and user tasks

Minix services:

  • rs: Reincarnation Server
  • ds: Data Store
  • ipc: shared memory and semaphore
  • sched: scheduler
  • vfs: Virtual File Systems
  • vm: Virtual Memory
  • is: System Information Service
  • mib: Manage Information Base
  • pm: Process Manager
  • drivers, filesystems, …


kernel IPC

Minix kernel provides interface for IPC and kernel call. System services can do kernel IPC and kernel calls, but user process can only do kernel IPC.
Kernel IPC delivers 64 bytes message between processes.

  • send: if receiver is not receiving, it will block
  • receive: if no messages is sending, it will block
  • sendrec: send and receive
  • sendnb: non-blocking send
  • senda: async send
  • notify: no message

kernel safecopy

Copying data between processes is done by safecopy kernel call.

  • Process A grants some memory in its own address space to process B
  • Process B calls safecopy to read/write that memory


  • Process C grants some memory in process A’s address space to process B
  • Process B calls safecopy to read/write that memory

safecopy first verifies the grants, and then creates temporary mapping and copy the data.

example: sys_read

  • user process calls sys_read
    sys_read constructs read request message, and send that message to vfs by kernel IPC (ipc_sendrec).

  • vfs sends read request to mfs
    vfs receives the message from user, grants user buffer to mfs, and sends read request to mfs

  • mfs reads data from block device driver and writes data to user buffer using safecopy


shared memory and semaphore

Service ipc manages shared mamory and semaphore.