시스템 프로그래밍 01.리눅스/유닉스 시스템 프로그래밍의 이해

01. 리눅스/유닉스 시스템 프로그래밍이란

- 시스템에서 제공하는 시스템 콜을 이용해 프로그램 작성하기 

-대다수 시스템 프로그래밍은 리눅스 기반으로 진행됨

 

02. 리눅스/ 유닉스 시스템 표준

- POSIX라는 유닉스 기반 인터페이스에 대한 이해 필요

- ANSI C 표준을 준수해야 한다

- 리눅스에서 안드로이드 등 우리가 일반적으로 많이 쓰는 운영체제들도 많이 파생되었다.

 

03. 시스템 프로그래밍

- 시스템 호출과 C언어 라이브러리는 실행 과정이 다르다.

- man 명령어를 통해 각 함수가 시스템 호출인지 라이브러리 함수인지 알 수 있다.

- 명령어에 대한 설명은 1번, 시스템 호출은 2번, 라이브러리 함수는 3번 섹션에 위치하고 있다.

- errno-base.h에서 오류 코드 확인할 수 있다.

#ifndef _ASM_GENERIC_ERRNO_BASE_H
#define _ASM_GENERIC_ERRNO_BASE_H

#define        EPERM                 1        /* Operation not permitted */
#define        ENOENT                 2        /* No such file or directory */
#define        ESRCH                 3        /* No such process */
#define        EINTR                 4        /* Interrupted system call */
#define        EIO                 5        /* I/O error */
#define        ENXIO                 6        /* No such device or address */
#define        E2BIG                 7        /* Argument list too long */
#define        ENOEXEC                 8        /* Exec format error */
#define        EBADF                 9        /* Bad file number */
#define        ECHILD                10        /* No child processes */
#define        EAGAIN                11        /* Try again */
#define        ENOMEM                12        /* Out of memory */
#define        EACCES                13        /* Permission denied */
#define        EFAULT                14        /* Bad address */
#define        ENOTBLK                15        /* Block device required */
#define        EBUSY                16        /* Device or resource busy */
#define        EEXIST                17        /* File exists */
#define        EXDEV                18        /* Cross-device link */
#define        ENODEV                19        /* No such device */
#define        ENOTDIR                20        /* Not a directory */
#define        EISDIR                21        /* Is a directory */
#define        EINVAL                22        /* Invalid argument */
#define        ENFILE                23        /* File table overflow */
#define        EMFILE                24        /* Too many open files */
#define        ENOTTY                25        /* Not a typewriter */
#define        ETXTBSY                26        /* Text file busy */
#define        EFBIG                27        /* File too large */
#define        ENOSPC                28        /* No space left on device */
#define        ESPIPE                29        /* Illegal seek */
#define        EROFS                30        /* Read-only file system */
#define        EMLINK                31        /* Too many links */
#define        EPIPE                32        /* Broken pipe */
#define        EDOM                33        /* Math argument out of domain of func */
#define        ERANGE                34        /* Math result not representable */

#endif

 

04. 시스템 도구

- vi test.c 등으로 파일 열람 가능

- makefile로 여러 파일을 한꺼번에 컴파일 가능

 

 

-오류 메시지 출력: perror(3)

PERROR(3)                                                                            Linux Programmer's Manual                                                                           PERROR(3)

NAME
       perror - print a system error message

SYNOPSIS
       #include <stdio.h>

       void perror(const char *s);

       #include <errno.h>

       const char * const sys_errlist[];
       int sys_nerr;
       int errno;       /* Not really declared this way; see errno(3) */

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sys_errlist, sys_nerr:
           From glibc 2.19 to 2.31:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE

 

 

- 오류 메시지 출력: stderror(3)

STRERROR(3)                                                                          Linux Programmer's Manual                                                                         STRERROR(3)

NAME
       strerror, strerrorname_np, strerrordesc_np, strerror_r, strerror_l - return string describing error number

SYNOPSIS
       #include <string.h>

       char *strerror(int errnum);
       const char *strerrorname_np(int errnum);
       const char *strerrordesc_np(int errnum);

       int strerror_r(int errnum, char *buf, size_t buflen);
                   /* XSI-compliant */

       char *strerror_r(int errnum, char *buf, size_t buflen);
                   /* GNU-specific */

       char *strerror_l(int errnum, locale_t locale);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strerrorname_np(), strerrordesc_np():
           _GNU_SOURCE
       strerror_r():
           The XSI-compliant version is provided if:
           (_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE
           Otherwise, the GNU-specific version is provided.

 

 

- 메모리 할당: malloc(3)

MALLOC(3)                                                                            Linux Programmer's Manual                                                                           MALLOC(3)

NAME
       malloc, free, calloc, realloc, reallocarray - allocate and free dynamic memory

SYNOPSIS
       #include <stdlib.h>

       void *malloc(size_t size);
       void free(void *ptr);
       void *calloc(size_t nmemb, size_t size);
       void *realloc(void *ptr, size_t size);
       void *reallocarray(void *ptr, size_t nmemb, size_t size);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       reallocarray():
           Since glibc 2.29:
               _DEFAULT_SOURCE
           Glibc 2.28 and earlier:
               _GNU_SOURCE

 

 

- 메모리 할당과 초기화: calloc(3), 메모리 추가 할당: realloc(3), 메모리 해제: free(3)

MALLOC(3)                                                                            Linux Programmer's Manual                                                                           MALLOC(3)

NAME
       malloc, free, calloc, realloc, reallocarray - allocate and free dynamic memory

SYNOPSIS
       #include <stdlib.h>

       void *malloc(size_t size);
       void free(void *ptr);
       void *calloc(size_t nmemb, size_t size);
       void *realloc(void *ptr, size_t size);
       void *reallocarray(void *ptr, size_t nmemb, size_t size);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       reallocarray():
           Since glibc 2.29:
               _DEFAULT_SOURCE
           Glibc 2.28 and earlier:
               _GNU_SOURCE

 

 

- 옵션 처리: getopt(3)

GETOPT(1)                                                                                  User Commands                                                                                 GETOPT(1)

NAME
       getopt - parse command options (enhanced)

SYNOPSIS
       getopt optstring parameters getopt [options] [--] optstring parameters getopt [options] -o|--options optstring [options] [--] parameters

DESCRIPTION
       getopt is used to break up (parse) options in command lines for easy parsing by shell procedures, and to check for valid options. It uses the GNU getopt(3) routines to do this.

       The parameters getopt is called with can be divided into two parts: options which modify the way getopt will do the parsing (the options and the optstring in the SYNOPSIS), and the
       parameters which are to be parsed (parameters in the SYNOPSIS). The second part will start at the first non-option parameter that is not an option argument, or after the first occurrence
       of '--'. If no '-o' or '--options' option is found in the first part, the first parameter of the second part is used as the short options string.

       If the environment variable GETOPT_COMPATIBLE is set, or if the first parameter is not an option (does not start with a '-', the first format in the SYNOPSIS), getopt will generate output
       that is compatible with that of other versions of getopt(1). It will still do parameter shuffling and recognize optional arguments (see section COMPATIBILITY for more information).

       Traditional implementations of getopt(1) are unable to cope with whitespace and other (shell-specific) special characters in arguments and non-option parameters. To solve this problem,
       this implementation can generate quoted output which must once again be interpreted by the shell (usually by using the eval command). This has the effect of preserving those characters,
       but you must call getopt in a way that is no longer compatible with other versions (the second or third format in the SYNOPSIS). To determine whether this enhanced version of getopt(1) is
       installed, a special test option (-T) can be used.