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As a static body of software, categorized by the functionality offered by the modules that make up the kernel
Context English Portuguese (Brazil) State
4.4BSD Facilities and the Kernel O kernel e as facilidades do 4.4BSD
The 4.4BSD kernel provides four basic facilities: processes, a filesystem, communications, and system startup. This section outlines where each of these four basic services is described in this book. O kernel 4.4BSD fornece quatro recursos básicos: processos, um sistema de arquivos, comunicações e inicialização do sistema. Esta seção descreve onde cada um desses quatro serviços básicos é descrito neste livro.
Processes constitute a thread of control in an address space. Mechanisms for creating, terminating, and otherwise controlling processes are described in Chapter 4. The system multiplexes separate virtual-address spaces for each process; this memory management is discussed in Chapter 5. Processos constituem uma thread de controle em um endereço de memória. Mecanismos para criação, finalização, e outras formas de controle de processos são descritos no Capítulo 4. O sistema multiplexa separados espaços de endereços virtuais para cada processo; esse gerenciamento de memória é discutido no Capítulo 5.
The user interface to the filesystem and devices is similar; common aspects are discussed in Chapter 6. The filesystem is a set of named files, organized in a tree-structured hierarchy of directories, and of operations to manipulate them, as presented in Chapter 7. Files reside on physical media such as disks. 4.4BSD supports several organizations of data on the disk, as set forth in Chapter 8. Access to files on remote machines is the subject of Chapter 9. Terminals are used to access the system; their operation is the subject of Chapter 10. A interface do usuário para o sistema de arquivos e dispositivos é similar; aspectos comuns são discutidos no Capítulo 6. O sistema de arquivos é um conjunto de arquivos nomeados, organizados em uma hierarquia de árvore-estruturada de diretórios, e de operações para manipulá-los, como apresentado no Capítulo 7. Arquivos residem em uma mídia física como discos. 4.4BSD suporta diversas organizações de dados no disco, como mostrado em frente no Capítulo 8. Acesso a arquivos em máquinas remotas é o assunto do capítulo 9. Terminais são usados para acessar o sistema; a operação deles é o assunto do Capítulo 10.
Communication mechanisms provided by traditional UNIX systems include simplex reliable byte streams between related processes (see pipes, Section 11.1), and notification of exceptional events (see signals, Section 4.7). 4.4BSD also has a general interprocess-communication facility. This facility, described in Chapter 11, uses access mechanisms distinct from those of the filesystem, but, once a connection is set up, a process can access it as though it were a pipe. There is a general networking framework, discussed in Chapter 12, that is normally used as a layer underlying the IPC facility. Chapter 13 describes a particular networking implementation in detail. Mecanismos de comunicação providos por sistemas tradicionais UNIX incluem confiáveis bytes streams simplex entre processos relacionados (veja pipes, Seção 11.1), e notificação de eventos excepcionais (veja signals, Seção 4.7). 4.4BSD também possui um mecanismo geral de comunicação interprocessual. Esse mecanismo, descrito no Capítulo 11, usa mecanismos de acessos distintos daqueles do sistema de arquivos, mas, uma vez que uma conexão é realizada, um processo pode acessá-la como se fosse um pipe. Existe um framework geral de rede, discutido no capítulo 12, que é normalmente usado como uma camada de base para o mecanismo IPC. O Capítulo 13 descreve uma implementação de rede particular em detalhe.
Any real operating system has operational issues, such as how to start it running. Startup and operational issues are described in Chapter 14.
Sections 2.3 through 2.14 present introductory material related to Chapters 3 through 14. We shall define terms, mention basic system calls, and explore historical developments. Finally, we shall give the reasons for many major design decisions.
The Kernel O Kernel
The <emphasis>kernel</emphasis> is the part of the system that runs in protected mode and mediates access by all user programs to the underlying hardware (e.g., CPU, disks, terminals, network links) and software constructs (e.g., filesystem, network protocols). The kernel provides the basic system facilities; it creates and manages processes, and provides functions to access the filesystem and communication facilities. These functions, called <emphasis>system calls</emphasis> appear to user processes as library subroutines. These system calls are the only interface that processes have to these facilities. Details of the system-call mechanism are given in Chapter 3, as are descriptions of several kernel mechanisms that do not execute as the direct result of a process doing a system call.
A <emphasis>kernel</emphasis> in traditional operating-system terminology, is a small nucleus of software that provides only the minimal facilities necessary for implementing additional operating-system services. In contemporary research operating systems -- such as Chorus <xref linkend="biblio-rozier"/>, Mach <xref linkend="biblio-accetta"/>, Tunis <xref linkend="biblio-ewens"/>, and the V Kernel <xref linkend="biblio-cheriton"/> -- this division of functionality is more than just a logical one. Services such as filesystems and networking protocols are implemented as client application processes of the nucleus or kernel.
The 4.4BSD kernel is not partitioned into multiple processes. This basic design decision was made in the earliest versions of UNIX. The first two implementations by Ken Thompson had no memory mapping, and thus made no hardware-enforced distinction between user and kernel space <xref linkend="biblio-ritchie"/>. A message-passing system could have been implemented as readily as the actually implemented model of kernel and user processes. The monolithic kernel was chosen for simplicity and performance. And the early kernels were small; the inclusion of facilities such as networking into the kernel has increased its size. The current trend in operating-systems research is to reduce the kernel size by placing such services in user space.
Users ordinarily interact with the system through a command-language interpreter, called a <emphasis>shell</emphasis>, and perhaps through additional user application programs. Such programs and the shell are implemented with processes. Details of such programs are beyond the scope of this book, which instead concentrates almost exclusively on the kernel.
Sections 2.3 and 2.4 describe the services provided by the 4.4BSD kernel, and give an overview of the latter's design. Later chapters describe the detailed design and implementation of these services as they appear in 4.4BSD.
Kernel Organization Organização do Kernel
In this section, we view the organization of the 4.4BSD kernel in two ways:
As a static body of software, categorized by the functionality offered by the modules that make up the kernel
By its dynamic operation, categorized according to the services provided to users
The largest part of the kernel implements the system services that applications access through system calls. In 4.4BSD, this software has been organized according to the following:
Basic kernel facilities: timer and system-clock handling, descriptor management, and process management
Memory-management support: paging and swapping Suporte de gerenciamento de memória: paginação e troca
Generic system interfaces: the I/O, control, and multiplexing operations performed on descriptors
The filesystem: files, directories, pathname translation, file locking, and I/O buffer management
Terminal-handling support: the terminal-interface driver and terminal line disciplines
Interprocess-communication facilities: sockets Instalações de comunicação entre processos: soquetes
Support for network communication: communication protocols and generic network facilities, such as routing
Machine-independent software in the 4.4BSD kernel Software independente de máquina no kernel 4.4BSD
Category Categoria
Lines of code Linhas de código
Percentage of kernel Porcentagem do kernel
total machine independent total independente da máquina
162,617 162,617


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