内核FAQ

1、 我编译内核时选了声卡支持，还把oss加入了模块，为什么出如下问题！
2、 bootsect.s 中的一个小问题：movsw的问题
3、 0x20,&timer_interrupt它在哪里做过schedule
4、 linux每10ms中断一次，它在哪里做了schedule()
5、 编译核心后的问题：xwindow-->console看不见！
6、 kernel_thread
7、 请问如何得到linux下的命令代码

1、我编译内核时选了声卡支持，还把oss加入了模块，为什么出如下问题！

我编译内核时选了声卡支持，还把oss加入了模块，为什么出如下问题！
信息是:
you dont seem to have a kernel with sound module
enabled,

你编译内核时是不是把声卡安模块方式编译

我声卡支持选择的是y
oss选择的是m
我的声卡买了是YMH734的，可是查出是Aztech的声卡，
以前用oss试过也没没用，不知您有没有装过这种烂声卡！

这样整一遍内核看行不行：
#make mrproper
#make clean
#make menuconfig
在模块的选项中全选为Yes,即 <*>或

方式
声卡这部分中：
sound card support选

• 
  其它的都选[M]
  保存退出后，
  #make dep
  #make bzImage
  #make modules
  #make modules_install
  为了系统能找到你编译的模块，(以2.4.2为例)将所生成的
  模块从/lib/modules/2.4.2/misc/中cp到/lib/modules/misc/
  然后再probe你的soundcoard,也许能成功。
  
  2、bootsect.s 中的一个小问题：movsw的问题
  
  ibm的汇编中，movsw进行的操作是：((DI))<-((SI))，那么在at&t汇编中呢？movsw指令进行什么操作呢？
  
  CPU所干的事永远是一样的，不过汇编文法的格式不同而已。
  some example:
  movw %bx,%ax //mov ax,bx
  xorl %eax,%eax //xor eax,eax
  movw $1,%ax //mov ax,1
  movb x,%ah //mov ah,byte ptr x
  movw x,%ax //mov ax,word ptr x
  movl x,%eax //mov eax,x
  b(8-bit),w(16-bit),l(32-bit)
  Most opcodes are identical between AF&T and Intel format,except for
  these:
  movsSD //movsx
  movzSD //movz
  S,D are the source and destinaion operand size suffixes.
  
  movswl %ax,%ecx //movsx ecx,ax
  Maybe mean something to you!!
  
  3、0x20,&timer_interrupt
  
  0x20,&timer_interrupt它在哪里做过schedule
  
  100个中断/秒（即10ms)每次中断都可能schedule(),许多其它情况也会引起schedule(),比如程序在资源缺乏时会主动请求重新调度，以让出CPU。0x20 timer_interrupt的大致过程如下：
  
  来时钟中断－－＞保存现场－－＞标记信息－－＞do_bottomhalf-－－＞应该重新调度吗？
  Yes－－＞调度
  No －－＞从中断返回
  
  4、linux每10ms中断一次，它在哪里做了schedule()
  
  linux每10ms中断一次，它在哪里做了schedule()。
  
  每当一个系统调用或中断完成时，将调用ret_from_sys_call（）,其中有一句：
  cmpl $0,__need_resched
  jne reschedule
  进行调度，时钟中断没10ms一次返回时依据具体情况进行调度选择。
  
  5、编译核心后的问题：xwindow-->console看不见！
  
  我编译了2.4.2，编译过程中一切正常，但重新用新内核启动后，可以进入console和xwindow，但是进入了xwindow后，我用Ctrl+Alt+Backspace想回到console，却黑屏，无论进行什么操作都不行。但是可以使用Ctrl+Alt+Del重新启动，stop过程中也是什么都看不到，但这个命令可以起作用。我用的是RedHat7.0，请各位大侠帮忙！谢谢！
  
  极有可能是显示模式切换与设置时出了问题，建议你：
  #cp /etc/X11/XF86Config /etc/X11/XF86Config_save_00
  #xf86config
  
  重新配置一遍X系统，看行不行
  
  6、kernel_thread
  
  kernel_thread(int.....)
  {
  .
  .
  .
  cmp %%sp,%%si
  je 1f 这里是不是永远都会跳到1：？？？？？？？
  .
  .
  .
  .
  1:
  
  kernel_thread调用clone系统调用创建一个新的进程（根据标志决定是用同一个进程号或另一个进程号），clone实际完成和fork几乎相同的工作，根据返回值为零和非零决定当前是新创建进程和父进程，父进程则跳转到1，新进程则调用fn函数，对照fork应该可以理解，另外三个“：”后面涉及一些linux下汇编的mov语法，你最好熟悉一下。
  
  7、请问如何得到linux下的命令代码
  
  请问如何得到linux下的各种命令的代码，例如ping,adduser
  
  系统中并没有提供，你只有从网上自己找了
  
  ping源码：
  * PING.C
  /*
  /* ping source code distribute by cpu || digger.
  /* for unix family only. compil and link success in sco unix.
  /* i think linux no problem too. u can try it.
  /* before read this code, you shoud know about the principle of
  /* tcp/ip, especially icmp protocol, u also should also know some
  /* about BSD socket API, and unix system signal programming.
  /*
  /* cc -o ping ping.c -lsocket, then u will get executable file,
  /* but must act as root when cc it, and then set euid attribute
  /* for this ping, then u can execute it as common user.
  /* because only root can have authority to creat raw socket.
  /*
  /* i love socket, if so do u,
  /* call me, cpu == digger
  
  # include
  # include
  # include
  # include
  # include
  # include
  # include
  # include
  # include
  # include
  
  # define ICMP_ECHO 8 /* icmp echo requir */
  # define ICMP_ECHOREPLY 0 /* icmp echo reply */
  # define ICMP_HEADSIZE 8 /* icmp packet header size */
  # define IP_HEADSIZE 20 /* ip packet header size */
  
  typedef struct tagIpHead /* icmp packet header */
  {
  u_char ip_verlen; /* ip version and ip header lenth*/
  u_char ip_tos; /* ip type of service */
  u_short ip_len; /* ip packet lenghth */
  u_short ip_id; /* ip packet identification */
  u_short ip_fragoff; /* ip packet fragment and offset */
  u_char ip_ttl; /* ip packet time to live */
  u_char ip_proto; /* ip packet protocol type */
  u_short ip_chksum; /* ip packet header checksum */
  u_long ip_src_addr; /* ip source ip adress */
  u_long ip_dst_addr; /* ip destination ip adress */
  } IPHEAD;
  
  typedef struct tagIcmpHead /* icmp header */
  {
  u_char icmp_type; /* icmp service type */
  /* 8 echo require, 0 echo reply */
  u_char icmp_code; /* icmp header code */
  u_short icmp_chksum; /* icmp header chksum */
  u_short icmp_id; /* icmp packet identification */
  u_short icmp_seq; /* icmp packet sequent */
  u_char icmp_data[1]; /* icmp data, use as pointer */
  } ICMPHEAD;
  
  u_short ChkSum( u_short * pIcmpData, int iDataLen )
  /* for check sum of icmp header */
  {
  u_short iSum;
  u_short iOddByte;
  
  iSum = 0;
  
  while ( iDataLen > 1 ) { /* xor the next unsigned int data */
  iSum ^= *pIcmpData++;
  iDataLen -= 2;
  }
  
  if ( iDataLen == 1 ) { /* the rest odd byte */
  iOddByte = 0;
  *((u_char *)&iOddByte) = *(u_char *)pIcmpData;
  iSum ^= iOddByte;
  }
  
  iSum ^= 0xffff; /* xor 0xffff == not it */
  return(iSum);
  }
  
  long time_now() /* return time passed by */
  /* since 1970.1.1 00:00:00, */
  /* in 1/1000000 second */
  {
  struct timeval now;
  long lPassed;
  gettimeofday(&now, 0);
  lPassed = now.tv_sec * 1000000 + now.tv_usec;
  /* now.tv_sec in second */
  /* now.tv_usec in 1/1000000 second */
  return lPassed;
  }
  
  char* host; /* destination host */
  char* prog; /* program name */
  extern errno; /* system global parameter */
  long lSendTime; /* each time when send, change it */
  u_short seq; /* the icmp packet seqence */
  int iTimeOut; /* time out parameter */
  int sock, sent, recvd, max, min, total;
  /* sent : icmp packet already sent */
  /* recvd: proper icmp packet received */
  /* max, min: max min round trip time */
  /* total: total round trip time */
  /* store to calculate average */
  u_long lHostIp; /* host ip adress */
  struct sockaddr_in it; /* destination host information */
  
  int ping();
  void stat();
  
  main(int argc, char** argv)
  {
  struct hostent* h;
  char buf[200];
  char dst_host[32];
  int i, namelen;
  IPHEAD* pIpHead;
  ICMPHEAD* pIcmpHead;
  
  if (argc <2) { /* ping the destination host */
  /* every timeout second */
  /* default timeout is 1 second */
  
  printf("usage: %s [-timeout] host|IP ", argv[0]);
  exit(0);
  }
  prog = argv[0];
  host = argc == 2 ? argv[1] : argv[2];
  iTimeOut = argc == 2 ? 1 : atoi(argv[1]);
  
  /* creat the raw socket for icmp */
  
  if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) <0) {
  perror("socket");
  exit(2);
  }
  
  /* set destination host information */
  
  bzero(&it, sizeof(it));
  it.sin_family = AF_INET;
  
  /* check host format */
  
  if ( ( lHostIp = inet_addr(host) ) != INADDR_NONE ) {
  /* is available ip adress */
  it.sin_addr.s_addr = lHostIp;
  strcpy( dst_host, host );
  } else if ( h = gethostbyname(host) ) {
  /* is available host name */
  /* from hosts file of local host */
  /* or from DNS */
  bcopy(h->h_addr, &it.sin_addr, h->h_length);
  sprintf( dst_host, "%s (%s)", host,
  inet_ntoa(it.sin_addr) );
  } else {
  /* bad ip adress or host name */
  /* exit */
  fprintf( stderr, "bad IP or host " );
  exit(3);
  }
  namelen = sizeof(it);
  
  printf(" Digger pinging %s, send %d bytes ",
  dst_host,
  IP_HEADSIZE + ICMP_HEADSIZE + sizeof(long)
  );
  
  seq = 0; /* first icmp_seq = 0 */
  sigset(SIGINT, stat); /* when press del or ctrl+c, call stat */
  /* to statistic the result , and then exit */
  sigset(SIGALRM, ping); /* hook ping function to timer */
  alarm(iTimeOut); /* start timer, call ping every timeout */
  /* seconds */
  ping();
  for ( ;; ) { /* waiting for every echo back */
  /* icmp packet and check it */
  register size;
  register u_char ttl;
  register delta;
  register iIpHeadLen;
  
  /* block to received echo back datagram */
  
  size = recvfrom(sock, buf, sizeof(buf), 0,
  (struct sockaddr *)&it, &namelen);
  if (size == -1 && errno == EINTR) {
  /* receive error or system call */
  /* interrupted */
  continue;
  }
  
  /* calculate the round trip time, */
  /* time when receive minus time when send */
  
  delta = (int)((time_now() - lSendTime)/1000);
  
  /* get echo back packet and check its ip header */
  
  pIpHead = (IPHEAD *)buf;
  
  /* get the ip packet lenth */
  /* if too small, not the icmp echoreply packet */
  /* give it up */
  
  iIpHeadLen = (int)((pIpHead->ip_verlen & 0x0f) <<2);
  if (size <iIpHeadLen + ICMP_HEADSIZE) {
  continue;
  }
  ttl = pIpHead->ip_ttl; /* time to live param */
  
  /* get the icmp header information */
  pIcmpHead = (ICMPHEAD *)(buf + iIpHeadLen);
  
  /* not icmp echo reply packet, give it up */
  if (pIcmpHead->icmp_type != ICMP_ECHOREPLY) {
  continue;
  }
  
  /* not proper icmp sequent number, give it up */
  if (pIcmpHead->icmp_id != seq || pIcmpHead->icmp_seq != seq) {
  continue;
  }
  
  /* print out result for each icmp */
  /* echo reply information */
  sprintf( buf, "icmp_seq=%u bytes=%d ttl=%d",
  pIcmpHead->icmp_seq, size, ttl );
  fprintf(stderr, "reply from %s: %s time=%d ms ",
  host, buf, delta);
  
  /* calculate some statistic information */
  /* max, min, average round trip time */
  /* received icmp echo reply packet numbers */
  max = MAX(delta, max);
  min = min ? MIN(delta, min) : delta;
  total += delta;
  ++ recvd;
  
  /* for next icmp sequence */
  
  ++ seq;
  }
  }
  
  ping()
  {
  char buf[200];
  int iPacketSize;
  
  /* make the icmp header information */
  
  ICMPHEAD *pIcmpHead = (ICMPHEAD *)buf;
  pIcmpHead->icmp_type = ICMP_ECHO;
  pIcmpHead->icmp_code = 0;
  pIcmpHead->icmp_id = seq;
  pIcmpHead->icmp_seq = seq;
  pIcmpHead->icmp_chksum = 0;
  
  /* store time information as icmp packet content, 4 bytes */
  /* u may store other information instead */
  
  *((long *)pIcmpHead->icmp_data) = time_now();
  
  iPacketSize = ICMP_HEADSIZE + 4; /* icmp packet length */
  
  /* icmp header check sum */
  
  pIcmpHead->icmp_chksum = ChkSum((u_short *)pIcmpHead,
  iPacketSize );
  
  /* remember the time when send for calculate round trip time */
  lSendTime = time_now();
  
  /* send the icmp packet to des host */
  if ( sendto(sock, buf, iPacketSize, 0, (struct sockaddr *)&it,
  sizeof(it) ) <0) {
  perror("send failed");
  exit(6);
  }
  
  /* packet number been sent */
  ++sent;
  
  /* reset the timer hooker to me again */
  alarm(iTimeOut);
  }
  
  void stat() /* print the statistic information for this time's ping */
  {
  if (sent) {
  printf(" ----- %s ping statistics summerized by Digger----- "
  , host );
  printf("%d packets sent, %d packets received, %.2f%% lost ",
  sent, recvd, (float)(sent-recvd)/(float)sent*100 );
  }
  if (recvd) {
  printf("round_trip min/avg/max: %d/%d/%d ms ",
  min, total/recvd, max );
  }
  exit(0);
  }
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