绋嬪簭8-8 linux/kernel/fork.c

  1 /*

  2  *  linux/kernel/fork.c

  3  *

  4  *  (C) 1991  Linus Torvalds

  5  */

  6

  7 /*

  8  *  'fork.c' contains the help-routines for the 'fork' system call

  9  * (see also system_call.s), and some misc functions ('verify_area').

 10  * Fork is rather simple, once you get the hang of it, but the memory

 11  * management can be a bitch. See 'mm/mm.c': 'copy_page_tables()'

 12  */

    /*

     * 'fork.c'涓�鍚�鏈夌郴缁熻皟鐢�'fork'鐨勮緟鍔╁瓙绋嬪簭锛堝弬瑙�system_call.s锛夛紝浠ュ強涓�浜�

     * 鍏朵粬鍑芥暟锛�'verify_area'锛夈�備竴鏃︿綘浜嗚В浜�fork锛屽氨浼氬彂鐜板畠鏄�闈炲父绠�鍗曠殑锛屼絾

     * 鍐呭瓨绠＄悊鍗存湁浜涢毦搴︺�傚弬瑙�'mm/memory.c'涓�鐨�'copy_page_tables()'鍑芥暟銆�

     */

 13 #include <errno.h>        // 閿欒��鍙峰ご鏂囦欢銆傚寘鍚�绯荤粺涓�鍚勭�嶅嚭閿欏彿銆�

 14

 15 #include <linux/sched.h>  // 璋冨害绋嬪簭澶存枃浠讹紝瀹氫箟浜嗕换鍔＄粨鏋�task_struct銆佷换鍔�0鐨勬暟鎹�銆�

 16 #include <linux/kernel.h> // 鍐呮牳澶存枃浠躲�傚惈鏈変竴浜涘唴鏍稿父鐢ㄥ嚱鏁扮殑鍘熷舰瀹氫箟銆�

 17 #include <asm/segment.h>  // 娈垫搷浣滃ご鏂囦欢銆傚畾涔変簡鏈夊叧娈靛瘎瀛樺櫒鎿嶄綔鐨勫祵鍏ュ紡姹囩紪鍑芥暟銆�

 18 #include <asm/system.h>   // 绯荤粺澶存枃浠躲�傚畾涔変簡璁剧疆鎴栦慨鏀规弿杩扮��/涓�鏂�闂ㄧ瓑鐨勫祵鍏ュ紡姹囩紪瀹忋��

 19

    // 鍐欓〉闈㈤獙璇併�傝嫢椤甸潰涓嶅彲鍐欙紝鍒欏�嶅埗椤甸潃�傚畾涔夊湪mm/memory.c 绗�261琛屽紑濮嬨��

 20 extern void write_verify(unsigned long address);

 21

 22 long last_pid=0;          // 鏈�鏂拌繘绋嬪彿锛屽叾鍊间細鐢�get_empty_process()鐢熸垚銆�

 23

    //// 杩涚▼绌洪棿鍖哄煙鍐欏墠楠岃瘉鍑芥暟銆�

    // 瀵逛簬80386 CPU锛屽湪鎵ц�岀壒鏉冪��0浠ｇ爜鏃朵笉浼氱悊浼氱敤鎴风┖闂翠腑鐨勯〉闈㈡槸鍚︽槸椤典繚鎶ょ殑锛屽洜姝�

    // 鍦ㄦ墽琛屽唴鏍镐唬鐮佹椂鐢ㄦ埛绌洪棿涓�鏁版嵁椤甸潰淇濇姢鏍囧織璧蜂笉浜嗕綔鐢�锛屽啓鏃跺�嶅埗鏈哄埗涔熷氨澶卞幓浜嗕綔鐢ㄣ��

    // verify_area()鍑芥暟灏辩敤浜庢�ょ洰鐨勩�備絾瀵逛簬80486鎴栧悗鏉ョ殑CPU锛屽叾鎺у埗瀵勫瓨鍣�CR0涓�鏈変竴涓�

    // 鍐欎繚鎶ゆ爣蹇�WP锛堜綅16锛夛紝鍐呮牳鍙�浠ラ�氳繃璁剧疆璇ユ爣蹇楁潵绂佹�㈢壒鏉冪��0鐨勪唬鐮佸悜鐢ㄦ埛绌洪棿鍙�璇�

    // 椤甸潰鎵ц�屽啓鏁版嵁锛屽惁鍒欏皢瀵艰嚧鍙戠敓鍐欎繚鎶ゅ紓甯搞�備粠鑰�486浠ヤ笂CPU鍙�浠ラ�氳繃璁剧疆璇ユ爣蹇楁潵杈�

    // 鍒颁娇鐢ㄦ湰鍑芥暟鍚屾牱鐨勭洰鐨勩��

    // 璇ュ嚱鏁板�瑰綋鍓嶈繘绋嬮�昏緫鍦板潃浠� addr 鍒� addr + size 杩欎竴娈佃寖鍥翠互椤典负鍗曚綅鎵ц�屽啓鎿嶄綔鍓�

    // 鐨勬��娴嬫搷浣溿�傜敱浜庢��娴嬪垽鏂�鏄�浠ラ〉闈�涓哄崟浣嶈繘琛屾搷浣滐紝鍥犳�ょ▼搴忛�栧厛闇�瑕佹壘鍑�addr鎵�鍦ㄩ〉

    // 闈㈠紑濮嬪湴鍧�start锛岀劧鍚� start鍔犱笂杩涚▼鏁版嵁娈靛熀鍧�锛屼娇杩欎釜start鍙樻崲鎴�CPU 4G绾挎�х┖

    // 闂翠腑鐨勫湴鍧�銆傛渶鍚庡惊鐜�璋冪��write_verify() 瀵规寚瀹氬ぇ灏忕殑鍐呭瓨绌洪棿杩涜�屽啓鍓嶉獙璇併�傝嫢椤甸潰

    // 鏄�鍙�璇荤殑锛屽垯鎵ц�屽叡浜�妫�楠屽拰澶嶅埗椤甸潰鎿嶄綔锛堝啓鏃跺�嶅埗锛夈��

 24 void verify_area(void * addr,int size)

 25 {

 26         unsigned long start;

 27

    // 棣栧厛灏嗚捣濮嬪湴鍧�start璋冩暣涓哄叾鎵�鍦ㄩ〉鐨勫乏杈圭晫寮�濮嬩綅缃�锛屽悓鏃剁浉搴斿湴璋冩暣楠岃瘉鍖哄煙澶у皬銆�

    // 涓嬪彞涓�鐨� start & 0xfff 鐢ㄦ潵鑾峰緱鎸囧畾璧峰�嬩綅缃�addr锛堜篃鍗�start锛夊湪鎵�鍦ㄩ〉闈�涓�鐨勫亸绉�

    // 鍊硷紝鍘熼獙璇佽寖鍥� size 鍔犱笂杩欎釜鍋忕Щ鍊煎嵆鎵╁睍鎴愪互 addr 鎵�鍦ㄩ〉闈㈣捣濮嬩綅缃�寮�濮嬬殑鑼冨洿鍊笺��

    // 鍥犳�ゅ�� 30琛屼笂 涔熼渶瑕佹妸楠岃瘉寮�濮嬩綅缃� start 璋冩暣鎴愰〉闈㈣竟鐣屽�笺�傚弬瑙佸墠闈㈢殑鍥锯�滃唴瀛橀獙

    // 璇佽寖鍥寸殑璋冩暣鈥濄��

 28         start = (unsigned long) addr;

 29         size += start & 0xfff;

 30         start &= 0xfffff000;               // 姝ゆ椂start鏄�褰撳墠杩涚▼绌洪棿涓�鐨勯�昏緫鍦板潃銆�

    // 涓嬮潰鎶� start 鍔犱笂杩涚▼鏁版嵁娈靛湪绾挎�у湴鍧�绌洪棿涓�鐨勮捣濮嬪熀鍧�锛屽彉鎴愮郴缁熸暣涓�绾挎�х┖闂翠腑鐨勫湴

    // 鍧�浣嶇疆銆傚�逛��Linux 0.1x鍐呮牳锛屽叾鏁版嵁娈靛拰浠ｇ爜娈靛湪绾挎�у湴鍧�绌洪棿涓�鐨勫熀鍧�鍜岄檺闀垮潎鐩稿悓銆�

    // 鐒跺悗寰�鐜�杩涜�屽啓椤甸潰楠岃瘉銆傝嫢椤甸潰涓嶅彲鍐欙紝鍒欏�嶅埗椤甸潃�傦紙mm/memory.c锛�274琛岋級

 31         start += get_base(current->ldt[2]);     // include/linux/sched.h锛�277琛屻��

 32         while (size>0) {

 33                 size -= 4096;

 34                 write_verify(start);

 35                 start += 4096;

 36         }

 37 }

 38

    // 澶嶅埗鍐呭瓨椤佃〃銆�

    // 鍙傛暟nr鏄�鏂颁换鍔″彿锛�p鏄�鏂颁换鍔℃暟鎹�缁撴瀯鎸囬拡銆傝�ュ嚱鏁颁负鏂颁换鍔″湪绾挎�у湴鍧�绌洪棿涓�璁剧疆浠ｇ��

    // 娈靛拰鏁版嵁娈靛熀鍧�銆侀檺闀匡紝骞跺�嶅埗椤佃〃銆�  鐢变簬Linux绯荤粺閲囩敤浜嗗啓鏃跺�嶅埗锛�copy on write锛�

    // 鎶�鏈�锛� 鍥犳�よ繖閲屼粎涓烘柊杩涚▼璁剧疆鑷�宸辩殑椤电洰褰曡〃椤瑰拰椤佃〃椤癸紝鑰屾病鏈夊疄闄呬负鏂拌繘绋嬪垎閰嶇墿鐞�

    // 鍐呭瓨椤甸潰銆傛�ゆ椂鏂拌繘绋嬩笌鍏剁埗杩涚▼鍏变韩鎵�鏈夊唴瀛橀〉闈��傛搷浣滄垚鍔熻繑鍥�0锛屽惁鍒欒繑鍥炲嚭閿欏彿銆�

 39 int copy_mem(int nr,struct task_struct * p)

 40 {

 41         unsigned long old_data_base,new_data_base,data_limit;

 42         unsigned long old_code_base,new_code_base,code_limit;

 43

    // 棣栧厛鍙栧綋鍓嶈繘绋嬪眬閮ㄦ弿杩扮�﹁〃涓�浠ｇ爜娈垫弿杩扮�﹀拰鏁版嵁娈垫弿杩扮�﹂」涓�鐨勬�甸檺闀匡紙瀛楄妭鏁帮級銆�

    // 0x0f鏄�浠ｇ爜娈甸�夋嫨绗︼紱0x17鏄�鏁版嵁娈甸�夋嫨绗︺�傜劧鍚庡彇褰撳墠杩涚▼浠ｇ爜娈靛拰鏁版嵁娈靛湪绾挎�у湴鍧�

    // 绌洪棿涓�鐨勫熀鍦板潃銆傜敱浜�Linux 0.12鍐呮牳杩樹笉鏀�鎸佷唬鐮佸拰鏁版嵁娈靛垎绔嬬殑鎯呭喌锛屽洜姝よ繖閲岄渶瑕�

    // 妫�鏌ヤ唬鐮佹�靛拰鏁版嵁娈靛熀鍧�鏄�鍚﹂兘鐩稿悓锛屽苟涓旇�佹眰鏁版嵁娈电殑闀垮害鑷冲皯涓嶅皬浜庝唬鐮佹�电殑闀垮��

    // 锛堝弬瑙佸浘5-12锛夛紝鍚﹀垯鍐呮牳鏄剧ず鍑洪敊淇℃伅锛屽苟鍋滄�㈣繍琛屻��

    // get_limit()鍜�get_base()瀹氫箟鍦�include/linux/sched.h绗�277琛屽拰279琛屽�勩��

 44         code_limit=get_limit(0x0f);

 45         data_limit=get_limit(0x17);

 46         old_code_base = get_base(current->ldt[1]);

 47         old_data_base = get_base(current->ldt[2]);

 48         if (old_data_base != old_code_base)

 49                 panic("We don't support separate I&D");

 50         if (data_limit < code_limit)

 51                 panic("Bad data_limit");

    // 鐒跺悗璁剧疆鍒涘缓涓�鐨勬柊杩涚▼鍦ㄧ嚎鎬у湴鍧�绌洪棿涓�鐨勫熀鍦板潃绛変簬锛�64MB * 鍏朵换鍔″彿锛夛紝骞剁敤璇ュ��

    // 璁剧疆鏂拌繘绋嬪眬閮ㄦ弿杩扮�﹁〃涓�娈垫弿杩扮�︿腑鐨勫熀鍦板潃銆傛帴鐫�璁剧疆鏂拌繘绋嬬殑椤电洰褰曡〃椤瑰拰椤佃〃椤癸紝

    // 鍗冲�嶅埗褰撳墠杩涚▼锛堢埗杩涚▼锛夌殑椤电洰褰曡〃椤瑰拰椤佃〃椤广�� 姝ゆ椂瀛愯繘绋嬪叡浜�鐖惰繘绋嬬殑鍐呭瓨椤甸潃��

    // 姝ｅ父鎯呭喌涓�copy_page_tables()杩斿洖0锛屽惁鍒欒〃绀哄嚭閿欙紝鍒欓噴鏀惧垰鐢宠�风殑椤佃〃椤广��

 52         new_data_base = new_code_base = nr * TASK_SIZE;

 53         p->start_code = new_code_base;

 54         set_base(p->ldt[1],new_code_base);

 55         set_base(p->ldt[2],new_data_base);

 56         if (copy_page_tables(old_data_base,new_data_base,data_limit)) {

 57                 free_page_tables(new_data_base,data_limit);

 58                 return -ENOMEM;

 59         }

 60         return 0;

 61 }

 62

 63 /*

 64  *  Ok, this is the main fork-routine. It copies the system process

 65  * information (task[nr]) and sets up the necessary registers. It

 66  * also copies the data segment in it's entirety.

 67  */

    /*

     * OK锛屼笅闈㈡槸涓昏�佺��fork瀛愮▼搴忋�傚畠澶嶅埗绯荤粺杩涚▼淇℃伅(task[n])

     * 骞朵笖璁剧疆蹇呰�佺殑瀵勫瓨鍣ㄣ�傚畠杩樻暣涓�鍦板�嶅埗鏁版嵁娈碉紙涔熸槸浠ｇ爜娈碉級銆�

     */

    // 澶嶅埗杩涚▼銆�

    // 璇ュ嚱鏁扮殑鍙傛暟鏄�杩涘叆绯荤粺璋冪敤涓�鏂�澶勭悊杩囩▼锛�sys_call.s锛夊紑濮嬶紝鐩村埌璋冪敤鏈�绯荤粺璋冪敤澶勭��

    // 杩囩▼锛�sys_call.s绗�208琛岋級鍜岃皟鐢ㄦ湰鍑芥暟鍓嶏紙sys_call.s绗�217琛岋級閫愭�ュ帇鍏ヨ繘绋嬪唴鏍�

    // 鎬佹爤鐨勫悇瀵勫瓨鍣ㄧ殑鍊笺�傝繖浜涘湪sys_call.s绋嬪簭涓�閫愭�ュ帇鍏ュ唴鏍告�佹爤鐨勫�硷紙鍙傛暟锛夊寘鎷�:

    // 鈶� CPU鎵ц�屼腑鏂�鎸囦护鍘嬪叆鐨勭敤鎴锋爤鍦板潃ss鍜�esp銆佹爣蹇�eflags鍜岃繑鍥炲湴鍧�cs鍜�eip锛�

    // 鈶� 绗�83--88琛屽湪鍒氳繘鍏�system_call鏃跺叆鏍堢殑娈靛瘎瀛樺櫒ds銆�es銆�fs鍜�edx銆�ecx銆�edx锛�

    // 鈶� 绗�94琛岃皟鐢�sys_call_table涓�sys_fork鍑芥暟鏃跺叆鏍堢殑杩斿洖鍦板潃锛堝弬鏁�none琛ㄧず锛夛紱

    // 鈶� 绗�212--216琛屽湪璋冪敤copy_process()涔嬪墠鍏ユ爤鐨�gs銆�esi銆�edi銆�ebp鍜�eax锛�nr锛夈��

    // 鍏朵腑鍙傛暟nr鏄�璋冪��find_empty_process()鍒嗛厤鐨勪换鍔℃暟缁勯」鍙枫��

 68 int copy_process(int nr,long ebp,long edi,long esi,long gs,long none,

 69                 long ebx,long ecx,long edx, long orig_eax,

 70                 long fs,long es,long ds,

 71                 long eip,long cs,long eflags,long esp,long ss)

 72 {

 73         struct task_struct *p;

 74         int i;

 75         struct file *f;

 76

    // 棣栧厛涓烘柊浠诲姟鏁版嵁缁撴瀯鍒嗛厤鍐呭瓨銆傚�傛灉鍐呭瓨鍒嗛厤鍑洪敊锛屽垯杩斿洖鍑洪敊鐮佸苟閫�鍑恒�傜劧鍚庡皢鏂颁换鍔�

    // 缁撴瀯鎸囬拡鏀惧叆浠诲姟鏁扮粍鐨�nr椤逛腑銆傚叾涓�nr涓轰换鍔″彿锛岀敱鍓嶉潰find_empty_process()杩斿洖銆�

    // 鎺ョ潃鎶婂綋鍓嶈繘绋嬩换鍔＄粨鏋勫唴瀹瑰�嶅埗鍒板垰鐢宠�峰埌鐨勫唴瀛橀〉闈�p寮�濮嬪�勩��

 77         p = (struct task_struct *) get_free_page();

 78         if (!p)

 79                 return -EAGAIN;

 80         task[nr] = p;

 81         *p = *current;  /* NOTE! this doesn't copy the supervisor stack */

                            /* 娉ㄦ剰锛佽繖鏍峰仛涓嶄細澶嶅埗瓒呯骇鐢ㄦ埛鍫嗘爤锛堝彧澶嶅埗杩涚▼缁撴瀯锛�*/

    // 闅忓悗瀵瑰�嶅埗鏉ョ殑杩涚▼缁撴瀯鍐呭�硅繘琛屼竴浜涗慨鏀癸紝浣滀负鏂拌繘绋嬬殑浠诲姟缁撴瀯銆傚厛灏嗘柊杩涚▼鐨勭姸鎬�

    // 缃�涓轰笉鍙�涓�鏂�绛夊緟鐘舵�侊紝浠ラ槻姝㈠唴鏍歌皟搴﹀叾鎵ц�屻�傜劧鍚庤�剧疆鏂拌繘绋嬬殑杩涚▼鍙�pid锛屽苟鍒濆��

    // 鍖栬繘绋嬭繍琛屾椂闂寸墖鍊肩瓑浜庡叾 priority鍊硷紙 涓�鑸�涓�15涓�鍢�鍡掞級銆傛帴鐫�澶嶄綅鏂拌繘绋嬬殑淇″彿

    // 浣嶅浘銆佹姤璀﹀畾鏃跺�笺�佷細璇濓紙session锛夐�嗗�兼爣蹇� leader銆� 杩涚▼鍙婂叾瀛愯繘绋嬪湪鍐呮牳鍜岀敤鎴�

    // 鎬佽繍琛屾椂闂寸粺璁″�硷紝杩樿�剧疆杩涚▼寮�濮嬭繍琛岀殑绯荤粺鏃堕棿start_time銆�

 82         p->state = TASK_UNINTERRUPTIBLE;

 83         p->pid = last_pid;           // 鏂拌繘绋嬪彿銆備篃鐢�find_empty_process()寰楀埌銆�

 84         p->counter = p->priority;    // 杩愯�屾椂闂寸墖鍊硷紙鍢�鍡掓暟锛夈��

 85         p->signal = 0;               // 淇″彿浣嶅浘銆�

 86         p->alarm = 0;                // 鎶ヨ�﹀畾鏃跺�硷紙鍢�鍡掓暟锛夈��

 87         p->leader = 0;               /* process leadership doesn't inherit */

                                         /* 杩涚▼鐨勯�嗗�兼潈鏄�涓嶈兘缁ф壙鐨� */

 88         p->utime = p->stime = 0;     // 鐢ㄦ埛鎬佹椂闂村拰鏍稿績鎬佽繍琛屾椂闂淬��

 89         p->cutime = p->cstime = 0;   // 瀛愯繘绋嬬敤鎴锋�佸拰鏍稿績鎬佽繍琛屾椂闂淬��

 90         p->start_time = jiffies;     // 杩涚▼寮�濮嬭繍琛屾椂闂达紙褰撳墠鏃堕棿婊寸瓟鏁帮級銆�

    // 鍐嶄慨鏀逛换鍔＄姸鎬佹��TSS 鏁版嵁锛堝弬瑙佸垪琛ㄥ悗璇存槑锛夈�傜敱浜庣郴缁熺粰浠诲姟缁撴瀯 p鍒嗛厤浜�1椤垫柊

    // 鍐呭瓨锛屾墍浠� (PAGE_SIZE + (long) p) 璁�esp0姝ｅソ鎸囧悜璇ラ〉椤剁��銆� ss0:esp0 鐢ㄤ綔绋嬪簭

    // 鍦ㄥ唴鏍告�佹墽琛屾椂鐨勬爤銆傚彟澶栵紝鍦ㄧ��3绔犱腑鎴戜滑宸茬粡鐭ラ亾锛屾瘡涓�浠诲姟鍦� GDT琛ㄤ腑閮芥湁涓や釜

    // 娈垫弿杩扮�︼紝涓�涓�鏄�浠诲姟鐨�TSS娈垫弿杩扮�︼紝鍙︿竴涓�鏄�浠诲姟鐨�LDT琛ㄦ�垫弿杩扮�︺�備笅闈�111琛�

    // 璇�鍙ュ氨鏄�鎶�GDT涓�鏈�浠诲姟LDT娈垫弿杩扮�︾殑閫夋嫨绗︿繚瀛樺湪鏈�浠诲姟鐨�TSS娈典腑銆傚綋CPU鎵ц��

    // 鍒囨崲浠诲姟鏃讹紝浼氳嚜鍔ㄤ粠TSS涓�鎶�LDT娈垫弿杩扮�︾殑閫夋嫨绗﹀姞杞藉埌ldtr瀵勫瓨鍣ㄤ腑銆�

 91         p->tss.back_link = 0;

 92         p->tss.esp0 = PAGE_SIZE + (long) p;  // 浠诲姟鍐呮牳鎬佹爤鎸囬拡銆�

 93         p->tss.ss0 = 0x10;           // 鍐呮牳鎬佹爤鐨勬�甸�夋嫨绗︼紙涓庡唴鏍告暟鎹�娈电浉鍚岋級銆�

 94         p->tss.eip = eip;            // 鎸囦护浠ｇ爜鎸囬拡銆�

 95         p->tss.eflags = eflags;      // 鏍囧織瀵勫瓨鍣ㄣ��

 96         p->tss.eax = 0;              // 杩欐槸褰�fork()杩斿洖鏃舵柊杩涚▼浼氳繑鍥�0鐨勫師鍥犳墍鍦ㄣ��

 97         p->tss.ecx = ecx;

 98         p->tss.edx = edx;

 99         p->tss.ebx = ebx;

100         p->tss.esp = esp;

101         p->tss.ebp = ebp;

102         p->tss.esi = esi;

103         p->tss.edi = edi;

104         p->tss.es = es & 0xffff;     // 娈靛瘎瀛樺櫒浠�16浣嶆湁鏁堛��

105         p->tss.cs = cs & 0xffff;

106         p->tss.ss = ss & 0xffff;

107         p->tss.ds = ds & 0xffff;

108         p->tss.fs = fs & 0xffff;

109         p->tss.gs = gs & 0xffff;

110         p->tss.ldt = _LDT(nr);       // 浠诲姟灞�閮ㄨ〃鎻忚堪绗︾殑閫夋嫨绗︼紙LDT鎻忚堪绗﹀湪GDT涓�锛夈��

111         p->tss.trace_bitmap = 0x80000000;       //锛堥珮16浣嶆湁鏁堬級銆�

    // 濡傛灉褰撳墠浠诲姟浣跨敤浜嗗崗澶勭悊鍣�锛屽氨淇濆瓨鍏朵笂涓嬫枃銆傛眹缂栨寚浠�clts鐢ㄤ簬娓呴櫎鎺у埗瀵勫瓨鍣�CR0

    // 涓�鐨勪换鍔″凡浜ゆ崲锛�TS锛夋爣蹇椼�傛瘡褰撳彂鐢熶换鍔″垏鎹�锛�CPU閮戒細璁剧疆璇ユ爣蹇椼�傝�ユ爣蹇楃敤浜庣�＄悊

    // 鏁板�﹀崗澶勭悊鍣�锛氬�傛灉璇ユ爣蹇楃疆浣嶏紝閭ｄ箞姣忎��ESC鎸囦护閮戒細琚�鎹曡幏锛堝紓甯�7锛夈�傚�傛灉鍗忓�勭悊

    // 鍣ㄥ瓨鍦ㄦ爣蹇�MP涔熷悓鏃剁疆浣嶇殑璇濓紝閭ｄ箞WAIT鎸囦护涔熶細鎹曡幏銆傚洜姝わ紝濡傛灉浠诲姟鍒囨崲鍙戠敓鍦ㄤ竴

    // 涓�ESC鎸囦护寮�濮嬫墽琛屼箣鍚庯紝鍒欏崗澶勭悊鍣ㄤ腑鐨勫唴瀹瑰氨鍙�鑳介渶瑕佸湪鎵ц�屾柊鐨�ESC鎸囦护涔嬪墠淇濆瓨

    // 璧锋潵銆傛崟鑾峰�勭悊鍙ユ焺浼氫繚瀛樺崗澶勭悊鍣ㄧ殑鍐呭�瑰苟澶嶄綅TS鏍囧織銆傛寚浠�fnsave鐢ㄤ簬鎶婂崗澶勭悊鍣�

    // 鐨勬墍鏈夌姸鎬佷繚瀛樺埌鐩�鐨勬搷浣滄暟鎸囧畾鐨勫唴瀛樺尯鍩熶腑锛�tss.i387锛夈��

112         if (last_task_used_math == current)

113                 __asm__("clts ; fnsave %0 ; frstor %0"::"m" (p->tss.i387));

 

    // 鎺ヤ笅鏉ュ�嶅埗杩涚▼椤佃〃銆傚嵆鍦ㄧ嚎鎬у湴鍧�绌洪棿涓�璁剧疆鏂颁换鍔′唬鐮佹�靛拰鏁版嵁娈垫弿杩扮�︿腑鐨勫熀鍧�

    // 鍜岄檺闀匡紝骞跺�嶅埗椤佃〃銆傚�傛灉鍑洪敊锛堣繑鍥炲�间笉鏄�0锛夛紝鍒欏�嶄綅浠诲姟鏁扮粍涓�鐩稿簲椤瑰苟閲婃斁涓�

    // 璇ユ柊浠诲姟鍒嗛厤鐨勭敤浜庝换鍔＄粨鏋勭殑鍐呭瓨椤点��

114         if (copy_mem(nr,p)) {              // 杩斿洖涓嶄负0琛ㄧず鍑洪敊銆�

115                 task[nr] = NULL;

116                 free_page((long) p);

117                 return -EAGAIN;

118         }

    // 濡傛灉鐖惰繘绋嬩腑鏈夋枃浠舵槸鎵撳紑鐨勶紝鍒欏皢瀵瑰簲鏂囦欢鐨勬墦寮�娆℃暟澧�1銆傚洜涓鸿繖閲屽垱寤虹殑瀛愯繘绋�

    // 浼氫笌鐖惰繘绋嬪叡浜�杩欎簺鎵撳紑鐨勬枃浠躲�傚皢褰撳墠杩涚▼锛堢埗杩涚▼锛夌殑pwd, root鍜�executable

    // 寮曠敤娆℃暟鍧囧��1銆備笌涓婇潰鍚屾牱鐨勯亾鐞嗭紝瀛愯繘绋嬩篃寮曠敤浜嗚繖浜�i鑺傜偣銆�

119         for (i=0; i<NR_OPEN;i++)

120                 if (f=p->filp[i])

121                         f->f_count++;

122         if (current->pwd)

123                 current->pwd->i_count++;

124         if (current->root)

125                 current->root->i_count++;

126         if (current->executable)

127                 current->executable->i_count++;

128         if (current->library)

129                 current->library->i_count++;

    // 闅忓悗鍦�GDT琛ㄤ腑璁剧疆鏂颁换鍔�TSS娈靛拰LDT娈垫弿杩扮�﹂」銆傝繖涓や釜娈电殑闄愰暱鍧囪��璁剧疆鎴�104

    // 瀛楄妭銆傚弬瑙� include/asm/system.h锛�52鈥�66 琛屼唬鐮併�� 鐒跺悗璁剧疆杩涚▼涔嬮棿鐨勫叧绯婚摼琛�

    // 鎸囬拡锛屽嵆鎶婃柊杩涚▼鎻掑叆鍒板綋鍓嶈繘绋嬬殑瀛愯繘绋嬮摼琛ㄤ腑銆傛妸鏂拌繘绋嬬殑鐖惰繘绋嬭�剧疆涓哄綋鍓嶈繘绋嬶��

    // 鎶婃柊杩涚▼鐨勬渶鏂板瓙杩涚▼鎸囬拡p_cptr 鍜屽勾杞诲厔寮熻繘绋嬫寚閽�p_ysptr缃�绌恒�傛帴鐫�璁╂柊杩涚▼

    // 鐨勮�佸厔杩涚▼鎸囬拡p_osptr璁剧疆绛変簬鐖惰繘绋嬬殑鏈�鏂板瓙杩涚▼鎸囬拡銆傝嫢褰撳墠杩涚▼鍗存槸杩樻湁鍏朵粬

    // 瀛愯繘绋嬶紝鍒欒�╂瘮閭昏�佸厔杩涚▼鐨勬渶骞磋交杩涚▼鎸囬拡p_yspter 鎸囧悜鏂拌繘绋嬨�傛渶鍚庢妸褰撳墠杩涚▼

    // 鐨勬渶鏂板瓙杩涚▼鎸囬拡鎸囧悜杩欎釜鏂拌繘绋嬨�傜劧鍚庢妸鏂拌繘绋嬭�剧疆鎴愬氨缁�鎬併�傛渶鍚庤繑鍥炴柊杩涚▼鍙枫��

    // 鍙﹀�栵�� set_tss_desc() 鍜� set_ldt_desc() 瀹氫箟鍦� include/asm/system.h 鏂囦欢涓�銆�

    // 鈥�gdt+(nr<<1)+FIRST_TSS_ENTRY鈥�鏄�浠诲��nr鐨�TSS鎻忚堪绗﹂」鍦ㄥ叏灞�琛ㄤ腑鐨勫湴鍧�銆傚洜涓�

    // 姣忎釜浠诲姟鍗犵敤GDT琛ㄤ腑2椤癸紝鍥犳�や笂寮忎腑瑕佸寘鎷�'(nr<<1)'銆�

    // 璇锋敞鎰忥紝鍦ㄤ换鍔″垏鎹㈡椂锛屼换鍔″瘎瀛樺櫒tr浼氱敱CPU鑷�鍔ㄥ姞杞姐��

130         set_tss_desc(gdt+(nr<<1)+FIRST_TSS_ENTRY,&(p->tss));

131         set_ldt_desc(gdt+(nr<<1)+FIRST_LDT_ENTRY,&(p->ldt));

132         p->p_pptr = current;               // 璁剧疆鏂拌繘绋嬬殑鐖惰繘绋嬫寚閽堛��

133         p->p_cptr = 0;                     // 澶嶄綅鏂拌繘绋嬬殑鏈�鏂板瓙杩涚▼鎸囬拡銆�

134         p->p_ysptr = 0;                    // 澶嶄綅鏂拌繘绋嬬殑姣旈偦骞磋交鍏勫紵杩涚▼鎸囬拡銆�

135         p->p_osptr = current->p_cptr;      // 璁剧疆鏂拌繘绋嬬殑姣旈偦鑰佸厔鍏勫紵杩涚▼鎸囬拡銆�

136         if (p->p_osptr)                    // 鑻ユ柊杩涚▼鏈夎�佸厔鍏勫紵杩涚▼锛屽垯璁╁叾

137                 p->p_osptr->p_ysptr = p;   // 骞磋交杩涚▼鍏勫紵鎸囬拡鎸囧悜鏂拌繘绋嬨��

138         current->p_cptr = p;               // 璁╁綋鍓嶈繘绋嬫渶鏂板瓙杩涚▼鎸囬拡鎸囧悜鏂拌繘绋嬨��

139         p->state = TASK_RUNNING;        /* do this last, just in case */

140         return last_pid;

141 }

142

    // 涓烘柊杩涚▼鍙栧緱涓嶉噸澶嶇殑杩涚▼鍙�last_pid銆傚嚱鏁拌繑鍥炲湪浠诲姟鏁扮粍涓�鐨勪换鍔″��(鏁扮粍椤�)銆�

143 int find_empty_process(void)

144 {

145         int i;

146

    // 棣栧厛鑾峰彇鏂扮殑杩涚▼鍙枫�傚�傛��last_pid澧�1鍚庤秴鍑鸿繘绋嬪彿鐨勬�ｆ暟琛ㄧず鑼冨洿锛屽垯閲嶆柊浠�1寮�濮�

    // 浣跨敤pid鍙枫�� 鐒跺悗鍦ㄤ换鍔℃暟缁勪腑鎼滅储鍒氳�剧疆鐨�pid鍙锋槸鍚﹀凡缁忚��浠讳綍浠诲姟浣跨敤銆傚�傛灉鏄�鍒�

    // 璺宠浆鍒板嚱鏁板紑濮嬪�勯噸鏂拌幏寰椾竴涓�pid鍙枫�� 鎺ョ潃鍦ㄤ换鍔℃暟缁勪腑涓烘柊浠诲姟瀵绘壘涓�涓�绌洪棽椤癸紝骞�

    // 杩斿洖椤瑰彿銆� last_pid鏄�涓�涓�鍏ㄥ眬鍙橀噺锛屼笉鐢ㄨ繑鍥炪�傚�傛灉姝ゆ椂浠诲姟鏁扮粍涓�64涓�椤瑰凡缁忚��鍏�

    // 閮ㄥ崰鐢�锛屽垯杩斿洖鍑洪敊鐮併��

147         repeat:

148                 if ((++last_pid)<0) last_pid=1;

149                 for(i=0 ; i<NR_TASKS ; i++)

150                         if (task[i] && ((task[i]->pid == last_pid) ||

151                                         (task[i]->pgrp == last_pid)))

152                                 goto repeat;

153         for(i=1 ; i<NR_TASKS ; i++)             // 浠诲姟0椤硅��鎺掗櫎鍦ㄥ�栥��

154                 if (!task[i])

155                         return i;

156         return -EAGAIN;

157 }

158