man 2部分的系统调用和操作系统内核所说的系统调用一样吗

zhongyj

比如我们读一个文件可以
#include <unistd.h>
read(fildes, buf, bytes)
这个可以用man -s2 read在shell中看它的格式，我的理解是man -s2出来的都是系统调用
操作系统内核的书中也有系统调用这个词，这两个是一样的吗。还是我们一般程序用read时，也只是OS所说系统调用的一个封装，执行read要先在用户态执行，然后到内核态执行。

Godbach

你的理解是有不同类型的系统调用吗，内核源码提供的一般称作内核API

zhongyj

我的意思是是不是我们一般用C语言编程时用open read write这些函数时（这个应该就叫系统调用吧）是不是就是内核API还是我们调的只是内核API的一个封装，调用内核API是库里面去调的

UnixStudier

man 2 部分的函数“应该”是系统调用，但是由于不同的操作系统实现不一样，也不一定就是系统调用。比如flock(2)，在某些系统上是使用fcntl实现。flock就只是一个函数，不是系统调用。

zhongyj

内核API
man -s2
man -s3
这三部分的关系到底是怎样的，有这方面解释的好书吗。

是不是man -s3的库函数都是用man -s2部分的函数来实现的
比如fopen内部调用open来实现。

benbenr

/usr/share/man : Manual pages
Purpose

This section details the organization for manual pages throughout the system, including /usr/share/man. Also refer to the section on /var/cache/man.

The primary <mandir> of the system is /usr/share/man. /usr/share/man contains manual information for commands and data under the / and /usr filesystems. [31]

Manual pages are stored in <mandir>/<locale>/man<section>/<arch>. An explanation of <mandir>, <locale>, <section>, and <arch> is given below.

A description of each section follows:

    *      man1: User programs Manual pages that describe publicly accessible commands are contained in this chapter. Most program documentation that a user will need to use is located here.
    *      man2: System calls This section describes all of the system calls (requests for the kernel to perform operations).
    *      man3: Library functions and subroutines Section 3 describes program library routines that are not direct calls to kernel services. This and chapter 2 are only really of interest to programmers.
    *      man4: Special files Section 4 describes the special files, related driver functions, and networking support available in the system. Typically, this includes the device files found in /dev and the kernel interface to networking protocol support.
    *      man5: File formats The formats for many data files are documented in the section 5. This includes various include files, program output files, and system files.
    *      man6: Games This chapter documents games, demos, and generally trivial programs. Different people have various notions about how essential this is.
    *      man7: Miscellaneous Manual pages that are difficult to classify are designated as being section 7. The troff and other text processing macro packages are found here.
    *      man8: System administration Programs used by system administrators for system operation and maintenance are documented here. Some of these programs are also occasionally useful for normal users.

这个可以么？

zhongyj

这个解释的不详细
还是去glibc了，看它调用什么实现的

ivhb

你用的solaris吧，
man -s 2 intro
man -s 3 intro

里面介绍的比较详细了

通常来说，2是system call，3是library和function
至于3是不是全部都是用2来实现的。这个未必。肯定有不少function是不需要系统服务界面的。

JohnBull

本质一样形式不一样。
man 2 所谓的系统调用是标准系统调用的C接口；内核提供原生的系统调用接口（如Linux的int80）。
glibc把原生接口封装成C接口。