探索MINIX源代码：include/ansi.h解析

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"Minix源代码提供了对MINIX操作系统内核及系统组件的深入理解机会。" MINIX是一款轻量级的类UNIX操作系统，由Andrew S. Tanenbaum教授设计，主要用于教学和研究目的。源代码的开放使得开发者和学生能够学习到操作系统设计和实现的细节。在提供的`include/ansi.h`文件中，我们看到了MINIX如何处理ANSI C标准的兼容性问题。在C语言的历史中，ANSI C（也称为C89或C90）是第一个标准化的C语言版本，它引入了许多重要的改进和规范，包括函数原型的强制使用。在`ansi.h`这个头文件中，MINIX尝试检测编译器是否支持ANSI C标准。如果编译器符合标准，文件会定义一个符号`_ANSI`，通常赋值为一个魔法数字（在这里是31459），以标识编译器具有足够的ANSI C兼容性。这个魔法数字可能是为了避免不必要的非标准扩展而设置的。如果`_ANSI`被定义，MINIX会提供一个宏`_PROTOTYPE(function, params)`，这个宏根据需要生成ANSI标准C的函数原型或者传统的K&R风格的函数声明。在早期的C编程中，函数原型的使用并不统一，K&R风格的函数声明允许函数参数不指定类型，这在ANSI C中已经被弃用，因为可能会导致类型检查错误和潜在的内存安全问题。 `_PROTOTYPE`宏的存在，使得MINIX的源代码可以在不同的编译环境中保持兼容性，无论是使用支持ANSI C的现代编译器，还是那些可能不完全符合标准的老式编译器。通过这种方式，MINIX的源代码可以在广泛的平台上编译和运行，这也是开源操作系统的一个重要优势。通过分析`ansi.h`，我们可以了解到MINIX是如何优雅地处理不同编译器的兼容性问题，并且在源代码中实现了一种向后兼容的策略。这对于理解操作系统的构建、C语言的标准化过程以及如何编写跨平台的代码至关重要。对于那些希望深入学习操作系统原理和C语言编程的人来说，MINIX的源代码是一个宝贵的资源。

516 File: include/termios.h MINIX SOURCE CODE

01155 /* Extensions to the termios c_lflag bit map. */

01156 #define LFLUSHO 0x0200 /* Flush output. */

01157

01158 /* Extensions to the c_cc array. */

01159 #define VREPRINT 11 /* cc_c[VREPRINT] (ˆR) */

01160 #define VLNEXT 12 /* cc_c[VLNEXT] (ˆV) */

01161 #define VDISCARD 13 /* cc_c[VDISCARD] (ˆO) */

01162

01163 /* Extensions to baud rate settings. */

01164 #define B57600 0x0100 /* 57600 baud */

01165 #define B115200 0x0200 /* 115200 baud */

01166

01167 /* These are the default settings used by the kernel and by ’stty sane’ */

01168

01169 #define TCTRL_DEF (CREAD | CS8 | HUPCL)

01170 #define TINPUT_DEF (BRKINT | ICRNL | IXON | IXANY)

01171 #define TOUTPUT_DEF (OPOST | ONLCR)

01172 #define TLOCAL_DEF (ISIG | IEXTEN | ICANON | ECHO | ECHOE)

01173 #define TSPEED_DEF B9600

01174

01175 #define TEOF_DEF ’\4’ /* ˆD */

01176 #define TEOL_DEF _POSIX_VDISABLE

01177 #define TERASE_DEF ’\10’ /* ˆH */

01178 #define TINTR_DEF ’\3’ /* ˆC */

01179 #define TKILL_DEF ’\25’ /* ˆU */

01180 #define TMIN_DEF 1

01181 #define TQUIT_DEF ’\34’ /* ˆ\ */

01182 #define TSTART_DEF ’\21’ /* ˆQ */

01183 #define TSTOP_DEF ’\23’ /* ˆS */

01184 #define TSUSP_DEF ’\32’ /* ˆZ */

01185 #define TTIME_DEF 0

01186 #define TREPRINT_DEF ’\22’ /* ˆR */

01187 #define TLNEXT_DEF ’\26’ /* ˆV */

01188 #define TDISCARD_DEF ’\17’ /* ˆO */

01189

01190 /* Window size. This information is stored in the TTY driver but not used.

01191 * This can be used for screen based applications in a window environment.

01192 * The ioctls TIOCGWINSZ and TIOCSWINSZ can be used to get and set this

01193 * information.

01194 */

01195

01196 struct winsize

01197 {

01198 unsigned short ws_row; /* rows, in characters */

01199 unsigned short ws_col; /* columns, in characters */

01200 unsigned short ws_xpixel; /* horizontal size, pixels */

01201 unsigned short ws_ypixel; /* vertical size, pixels */

01202 };

01203 #endif /* _MINIX */

01204

01205 #endif /* _TERMIOS_H */

MINIX SOURCE CODE File: include/timers.h 517

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

include/timers.h

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

01300 /* This library provides generic watchdog timer management functionality.

01301 * The functions operate on a timer queue provided by the caller. Note that

01302 * the timers must use absolute time to allow sorting. The library provides:

01303 *

01304 * tmrs_settimer: (re)set a new watchdog timer in the timers queue

01305 * tmrs_clrtimer: remove a timer from both the timers queue

01306 * tmrs_exptimers: check for expired timers and run watchdog functions

01307 *

01308 * Author:

01309 * Jorrit N. Herder <jnherder@cs.vu.nl>

01310 * Adapted from tmr_settimer and tmr_clrtimer in src/kernel/clock.c.

01311 * Last modified: September 30, 2004.

01312 */

01313

01314 #ifndef _TIMERS_H

01315 #define _TIMERS_H

01316

01317 #include <limits.h>

01318 #include <sys/types.h>

01319

01320 struct timer;

01321 typedef void (*tmr_func_t)(struct timer *tp);

01322 typedef union { int ta_int; long ta_long; void *ta_ptr; } tmr_arg_t;

01323

01324 /* A timer_t variable must be declare for each distinct timer to be used.

01325 * The timers watchdog function and expiration time are automatically set

01326 * by the library function tmrs_settimer, but its argument is not.

01327 */

01328 typedef struct timer

01329 {

01330 struct timer *tmr_next; /* next in a timer chain */

01331 clock_t tmr_exp_time; /* expiration time */

01332 tmr_func_t tmr_func; /* function to call when expired */

01333 tmr_arg_t tmr_arg; /* random argument */

01334 } timer_t;

01335

01336 /* Used when the timer is not active. */

01337 #define TMR_NEVER ((clock_t) -1 < 0) ? ((clock_t) LONG_MAX) : ((clock_t) -1)

01338 #undef TMR_NEVER

01339 #define TMR_NEVER ((clock_t) LONG_MAX)

01340

01341 /* These definitions can be used to set or get data from a timer variable. */

01342 #define tmr_arg(tp) (&(tp)->tmr_arg)

01343 #define tmr_exp_time(tp) (&(tp)->tmr_exp_time)

01344

01345 /* Timers should be initialized once before they are being used. Be careful

01346 * not to reinitialize a timer that is in a list of timers, or the chain

01347 * will be broken.

01348 */

01349 #define tmr_inittimer(tp) (void)((tp)->tmr_exp_time = TMR_NEVER, \

01350 (tp)->tmr_next = NULL)

01351

01352 /* The following generic timer management functions are available. They

01353 * can be used to operate on the lists of timers. Adding a timer to a list

01354 * automatically takes care of removing it.

MINIX SOURCE CODE File: include/sys/types.h 519

01445 /* Open Group Base Specifications Issue 6 (not complete) */

01446 typedef long useconds_t; /* Time in microseconds */

01447

01448 /* Types used in disk, inode, etc. data structures. */

01449 typedef short dev_t; /* holds (major|minor) device pair */

01450 typedef char gid_t; /* group id */

01451 typedef unsigned long ino_t; /* i-node number (V3 filesystem) */

01452 typedef unsigned short mode_t; /* file type and permissions bits */

01453 typedef short nlink_t; /* number of links to a file */

01454 typedef unsigned long off_t; /* offset within a file */

01455 typedef int pid_t; /* process id (must be signed) */

01456 typedef short uid_t; /* user id */

01457 typedef unsigned long zone_t; /* zone number */

01458 typedef unsigned long block_t; /* block number */

01459 typedef unsigned long bit_t; /* bit number in a bit map */

01460 typedef unsigned short zone1_t; /* zone number for V1 file systems */

01461 typedef unsigned short bitchunk_t; /* collection of bits in a bitmap */

01462

01463 typedef unsigned char u8_t; /* 8 bit type */

01464 typedef unsigned short u16_t; /* 16 bit type */

01465 typedef unsigned long u32_t; /* 32 bit type */

01466

01467 typedef char i8_t; /* 8 bit signed type */

01468 typedef short i16_t; /* 16 bit signed type */

01469 typedef long i32_t; /* 32 bit signed type */

01470

01471 typedef struct { u32_t _[2]; } u64_t;

01472

01473 /* The following types are needed because MINIX uses K&R style function

01474 * definitions (for maximum portability). When a short, such as dev_t, is

01475 * passed to a function with a K&R definition, the compiler automatically

01476 * promotes it to an int. The prototype must contain an int as the parameter,

01477 * not a short, because an int is what an old-style function definition

01478 * expects. Thus using dev_t in a prototype would be incorrect. It would be

01479 * sufficient to just use int instead of dev_t in the prototypes, but Dev_t

01480 * is clearer.

01481 */

01482 typedef int Dev_t;

01483 typedef int _mnx_Gid_t;

01484 typedef int Nlink_t;

01485 typedef int _mnx_Uid_t;

01486 typedef int U8_t;

01487 typedef unsigned long U32_t;

01488 typedef int I8_t;

01489 typedef int I16_t;

01490 typedef long I32_t;

01491

01492 /* ANSI C makes writing down the promotion of unsigned types very messy. When

01493 * sizeof(short) == sizeof(int), there is no promotion, so the type stays

01494 * unsigned. When the compiler is not ANSI, there is usually no loss of

01495 * unsignedness, and there are usually no prototypes so the promoted type

01496 * doesn’t matter. The use of types like Ino_t is an attempt to use ints

01497 * (which are not promoted) while providing information to the reader.

01498 */

01499

01500 typedef unsigned long Ino_t;

01501

01502 #if _EM_WSIZE == 2

01503 /*typedef unsigned int Ino_t; Ino_t is now 32 bits */

01504 typedef unsigned int Zone1_t;

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MIG_29UK

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