Mac OS X. Mach in the Darwin Kernel. COMP342 4/5/06

Transcription

1 Mac OS X Mach in the Darwin Kernel COMP342 4/5/06 Daniel A. Steffen Mathematics Department Macquarie University steffen@maths.mq.edu.au

2 Mach in the Darwin Kernel Overview of Mac OS X & Darwin Kernel Darwin Kernel Services Mach History & Goals Mach Abstractions in detail

3 Mac OS X System Architecture Classic Quartz Java OpenGL Darwin Carbon Cocoa QuickTime High Level APIs Frameworks Application Services Core Services Darwin Kernel CoreOS

4 Darwin Kernel Architecture Darwin Kernel Application Environments Darwin Classic Quartz File System Java OpenGL Carbon Darwin Network KEXT BSD Kernel Mach Kernel Cocoa QuickTime Drivers IOKit hybrid kernel: single address space for BSD and Mach (not a true microkernel system) processor architecture independent open-source

5 Darwin Kernel Architecture Origins - Mach 3.0 (OSFMK73) - Virtual Memory, Scheduling, IPC - 4.4BSD-Lite 2 - Process model, security, file access - FreeBSD 3.2 & Networking, NFS

6 Darwin Kernel Services cross-layer view Process Threads Scheduler File System Net KEXT KEXT Services Files VM IPC Security Drivers IOKit everything built on top of Mach primitives - e.g. BSD process is Mach task + extra structure lower-layer API not always safe to use on higher-layer objects

7 Mach Kernel microkernel architecturally, but tightly integrated CPU and memory abstractions manages processor and memory resources process & thread scheduling SMP & realtime support memory protection, management (VM) policy neutral message based: all interaction based on mach ports

8 BSD Kernel tight integration with Mach and IOKit filesystem & networking architecture process model: env vars, signals, reaping security policy: users, filesystem permissions POSIX/BSD API: pthreads, select, kqueues, plugin architecture for NKEs (e.g. filters) enhanced VFS design (metadata, ACLs, unicode, large files, UBC)

9 IO Kit abstraction level for driver and device access object-oriented framework: common behavior & protocols among device types abstracted into families, only device-specifics in drivers implemented in Embedded C++ modular and extensible, many families already implemented in OS, support for userspace drivers dynamic device management, on-demand driver matching & (un)loading, power management

10 Mach/Darwin History : Mach Research project at CMU : Mach 3 effort continued at OSF RI: OSF/1! DEC Digital UNIX! Compaq Tru : NeXTSTEP on Mach 2.5 & 4.3BSD 1997: Apple acquires NeXT 2000: Darwin 1.0 (Mac OS X DP4): kernel : MkLinux on Mach 3.0 by Apple & OSF transitioned to Mach 3.0 & 4.4BSD-Lite 2

11 Mach Goals simple, extensible communication kernel; BSD compatible ( drop-in replacement for BSD kernel) move as much functionality outside of kernel as possible (microkernel) small number of abstractions exploit parallelism in both OS and user applications extensive process to process communication (IPC) large, sparse address space support with flexible VM portability, multiprocessor & heterogeneous system support, distributed operation

12 Mach Abstractions Task: unit of resource ownership, has virtual address space & collection of port rights, contains threads Thread: unit of execution (CPU utilization), lightweight, shares containing task s resources Port: communication channel endpoint, accessible only via send / receive capabilities (port rights) Port set: group of ports on which a thread can block waiting to receive messages Message: typed collection of data objects/pointers Memory object: internal unit of memory management, tasks map portions into their address space

13 Mach Task Thread Mach Task Thread Virtual Memory Space Port Name Space Thread collection of system resources, which (except for address space) are referenced by ports and may be shared with other tasks if they have corresponding port rights provides a large, potentially sparse address space, portions of which may be shared through inheritance or external memory management contains some number of threads defines task wide exception handling

14 Mach Thread Mach Thread Register State Scheduling Attributes Exception Handlers point of flow control in a task, defines how and where of execution, but not the resources to execute with owns no resources, has access to all elements of the containing task potentially executes in parallel with other threads, even threads within the same task has minimal state for low overhead defines thread-specific exception handling

15 Mach Scheduler Mach Host CPU CPU assigns runnable threads to processors SMP: threads run on any available processor, preference for affinity Time Kernel Core GUI App fully preemptive scheduling - by higher priority threads when running in user mode - by higher priority real-time threads while running in kernel mode time constraint threads watched to assure good behavior

16 Mach Port unidirectional communication channel between a client requesting a service and a server providing that service has a single receiver and (potentially) multiple senders state associated with a port: message queue, count of port rights referencing it kernel has services to allocate ports, and every Mach entity (except virtual memory ranges) is named by a port, so ports are created implicitly during creation of such entities

17 Mach Port Right a port can only be accessed via a port right: an entity that indicates the right to access a specific port in a specific way three types of port rights: - receive: allows to receive messages from a port - send: allows to send messages to a port - send-once: allows to send a single message to a port port rights can be copied and moved between tasks via Mach messages can acquire certain port rights from a global service

18 Mach Message Virtual Memory Space Task Mach IPC Virtual Memory Space Task a typed collection of data passed between Message two queues entities not Semaphores, a Mach entity Locksets in its own right messages are queued, hold state between the time a message is sent Send, send-once and when it is received Receive messages can carry data (inline and out-of-line), Data (inline port and out-of-line) rights, virtual memory Additional ranges Mach port and rights sender identity information Sender identity information Mach ports are endpoints Capabilities represented by Mach port rights Messages carry

19 Mach Security Services implements mechanism, not policy no authentication checking capabilities in the form of Mach port rights subdivide capabilities to create extra privileges sender identity tagging on each message policy decisions implemented at the BSD level

20 Mach Memory Object represents non-resident state of given memory ranges memory manager: task implementing a memory object (responding to messages sent to its port), responsible for filling main memory with e.g. contents of backing store main memory is a cache for the contents of the various memory objects, kernel maintains cache by sending messages to the memory object ports Mach has no concept of files: BSD vnodes implemented on top of memory objects

21 Mach Address Space Mach Virtual Memory Services Mach controls most aspects of virtual memory Mach VM Services Address Space VM Object Cache Address Space defines the set of valid virtual addresses that a thread executing in a task is allowed to reference Each task s address space can be layout constructed flexibility with a unique layout protection against unauthorized Layout flexibility Protected address spaces access Guarded or update against unauthorized access or update copy-on-write Copy-on-Write optimization controlled sharing Controlled sharing semantics Single page, implemented mapped file, through actions to shared of memory complex regions manager for memory object of a memory range

22 References Apple developer information on Darwin Darwin source code Darwin Kernel Programming Guide on Mach - KernelProgramming/Mach/chapter_6_section_1.html - KernelProgramming/boundaries/chapter_14_section_4.html

23 References CMU Mach project - mach.html OSF Mach 3.0 manuals - osf.html Wikipedia: Mach kernel - kernelthread.com - M.K. McKusick et al, The Design and Implementation of the 4.4 BSD Operating System, Addison-Wesley, 1996

24 WWDC Scholarships to attend Apple s World Wide Developers Conference Aug Apple University Consortium scholarships for Australian university students and staff: (appls close 23/5/06) - Apple Developer Connection (ADC) Student program scholarships: (appls close 19/5/06) -

25 Acknowledgements The speaker gratefully acknowledges support to attend the Apple World Wide Developers Conference WWDC 2004 by the Apple University Consortium Australia - Graphics Credit - Jim Magee, Core OS Kernel Team, Apple Computer: - Slides from WWDC 2002 Session 107 The Darwin Kernel