//這是個很簡單的程序，完成qmail-send，qmail-clean,qmail-lspawn,qmail-rspawn,splogger
//的啟動，并通過管道將他們聯系在一起，當然不是網狀連接，具體如下
/*
	qmail-lspawn fd0 <-------	qmail-send fd1
	qmail-lspawn fd1 ------->	qmail-send fd2
	qmail-rspawn fd0 <-------	qmail-send fd3
	qmail-rspawn fd1 ------->	qmail-send fd4
	qmail-clean	 fd0 <-------	qmail-send fd5
	qmail-clean  fd1 ------->	qmail-send fd6

  理解他們之間的關系(注意方向)對于理解qmail-send源代碼非常重要，仔細再看一次。
  因為其比較簡單，所以這里就不對他的源代碼作過細的分析：
*/

#include "fd.h"#include "prot.h"#include "exit.h"#include "fork.h"#include "auto_uids.h"char *(qsargs[]) = { "qmail-send", 0 };char *(qcargs[]) = { "qmail-clean", 0 };char *(qlargs[]) = { "qmail-lspawn", "./Mailbox", 0 };char *(qrargs[]) = { "qmail-rspawn", 0 };void die() { _exit(111); }int pi0[2];		//splogger qmail int pi1[2];		//qmail-lspawn fd0 <-------- qmail-send fd1int pi2[2];		//qmail-lspawn fd1 --------> qmail-send fd2int pi3[2];		//qmail-rspawn fd0 <-------- qmail-send fd3int pi4[2];		//qmail-rspawn fd1 --------> qmail-send fd4int pi5[2];		//qmail-clean fd0 <-------- qmail-send fd5int pi6[2];		//qmail-clean fd1 --------> qmail-send fd6void close23456() { close(2); close(3); close(4); close(5); close(6); }
//因為沒有關閉pi0。所以所有的子進程都可以通過寫pi0來記錄maillogvoid closepipes() {  close(pi1[0]); close(pi1[1]); close(pi2[0]); close(pi2[1]);  close(pi3[0]); close(pi3[1]); close(pi4[0]); close(pi4[1]);  close(pi5[0]); close(pi5[1]); close(pi6[0]); close(pi6[1]);}void main(argc,argv)int argc;char **argv;{  if (chdir("/") == -1) die();  umask(077);  if (prot_gid(auto_gidq) == -1) die();  if (fd_copy(2,0) == -1) die();  if (fd_copy(3,0) == -1) die();  if (fd_copy(4,0) == -1) die();  if (fd_copy(5,0) == -1) die();  if (fd_copy(6,0) == -1) die();  if (argv[1]) {    qlargs[1] = argv[1];    ++argv;  }  if (argv[1]) {    if (pipe(pi0) == -1) die();    switch(fork()) {      case -1:	die();      case 0:        if (prot_gid(auto_gidn) == -1) die();        if (prot_uid(auto_uidl) == -1) die();        close(pi0[1]);        if (fd_move(0,pi0[0]) == -1) die();		//重定向pi0[0]到splogger的fd0        close23456();        execvp(argv[1],argv + 1);	//啟動splogger	die();    }    close(pi0[0]);    if (fd_move(1,pi0[1]) == -1) die();  }   if (pipe(pi1) == -1) die();  if (pipe(pi2) == -1) die();  if (pipe(pi3) == -1) die();  if (pipe(pi4) == -1) die();  if (pipe(pi5) == -1) die();  if (pipe(pi6) == -1) die();   switch(fork()) {		//啟動qmail-lspawn    case -1: die();    case 0:      if (fd_copy(0,pi1[0]) == -1) die();      if (fd_copy(1,pi2[1]) == -1) die();      close23456();      closepipes();      execvp(*qlargs,qlargs);      die();  }   switch(fork()) {		//啟動qmail-rspawn    case -1: die();    case 0:      if (prot_uid(auto_uidr) == -1) die();      if (fd_copy(0,pi3[0]) == -1) die();      if (fd_copy(1,pi4[1]) == -1) die();      close23456();      closepipes();      execvp(*qrargs,qrargs);      die();  }   switch(fork()) {		//啟動qmail-clean    case -1: die();    case 0:      if (prot_uid(auto_uidq) == -1) die();      if (fd_copy(0,pi5[0]) == -1) die();      if (fd_copy(1,pi6[1]) == -1) die();      close23456();      closepipes();      execvp(*qcargs,qcargs);      die();  }   if (prot_uid(auto_uids) == -1) die();  if (fd_copy(0,1) == -1) die();		//重定向管道，把qmail-send與上面個進程聯系起來  if (fd_copy(1,pi1[1]) == -1) die();  if (fd_copy(2,pi2[0]) == -1) die();  if (fd_copy(3,pi3[1]) == -1) die();  if (fd_copy(4,pi4[0]) == -1) die();  if (fd_copy(5,pi5[1]) == -1) die();  if (fd_copy(6,pi6[0]) == -1) die();  closepipes();  execvp(*qsargs,qsargs);		//最后啟動qmail-send  die();}