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Understanding the Role of MINIX System Task in OS Kernels, Study notes of Operating Systems

University of Nebraska–Lincoln (UNL)Operating Systems

An overview of the minix system task, a kernel service that performs tasks for the file system (fs) and memory manager (mm) in csce 351 operating system kernels. The system task communicates with fs and mm via message passing ipc and is implemented as a device driver task. The purpose of the system task, its functions, and two specific messages: sys_copy and sys_trace.

Typology: Study notes

Pre 2010

Uploaded on 08/30/2009

koofers-user-nrp
koofers-user-nrp 🇺🇸

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MINIX System Task
Steve Goddard
[email protected]
http://www.cse.unl.edu/~goddard/Courses/CSCE351
CSCE 351
Operating System Kernels
2
System Task Purpose
◆Perform kernel services for the File System (FS) and
Memory Manager (MM)
◆Communicates with FS and MM via the standard
message passing IPC
◆Implemented in Layer 2 (recall Fig 2-16) as a device
driver task (line 14837 is start of sys_task)
» Does not control an I/O device
» Implements an interface to the internal system
» Same privileges as I/O tasks and compiled in Kernel
» Notice that it always sends a reply to the sender, even if the
message request is invalid
pf3

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1

MINIX System Task

Steve Goddard

[email protected]

http://www.cse.unl.edu/~goddard/Courses/CSCE

CSCE 351

Operating System Kernels

System Task Purpose

u Perform kernel services for the File System (FS) and Memory Manager (MM) u Communicates with FS and MM via the standard message passing IPC u Implemented in Layer 2 (recall Fig 2-16) as a device driver task (line 14837 is start of sys_task) » Does not control an I/O device » Implements an interface to the internal system » Same privileges as I/O tasks and compiled in Kernel » Notice that it always sends a reply to the sender, even if the message request is invalid

3

System Task Functions

u Figure 3-50, page 297, lists 19 types of messages that the System Task receives and processes u We will only talk about two (three) of these: » SYS_COPY (and SYS_VCOPY) v Most heavily used message. v Copies data to/from user processes for FS and MM » SYS_TRACE v Sent by MM v Supports PTRACE system call, which is used for debugging

SYS_COPY

u Used to move data from FS or MM space to user space u Required since FS and MM cannot directly access user process space u SYS_COPY implemented with do_copy, which simply calls phys_copy u SYS_VCOPY accepts multiple SYS_COPY requests as a single message to reduce overhead