make -C

底下是用在 build mozilla 時用的，但是像 kernel 也是同樣的道理，參考一下

1) pull or update a tree from CVS
2) make -f client.mk build
3) go have lunch
4) make changes in foo/bar/
5) make -C foo/bar
6) repeat #4, #5

message queue example

多年來，在做嵌入式產品時，經驗上在網虎時代大家都用 message queue 機制來通訊，其實當時也還有其他的機制，但是底下的工具可以讓大家省點事，似乎後來就都採用這套方法，有興趣的人可以拿去用用看。

語法在程式中有提到





#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

#define MAX_TEXT 255

typedef struct my_msg_st {
   long int mtype;
   char mtext[MAX_TEXT];
} msgbuf;

int main(int argc, char *argv[])
{
 int msgid;
 int sz;
 int key;
 long int type;
 msgbuf mdata;
 char buffer[MAX_TEXT];

 if (argc == 1) {
   printf ("Usage: %s key [type [data]]\n", argv[0]);
   return 1;
 }

 key = atoi (argv[1]);
 msgid = msgget((key_t)key,0666|IPC_CREAT);

 if (msgid == -1) {
   return 2;
 }

 if (argc == 2) { // get all types
   if (msgrcv(msgid,(void *)&mdata, MAX_TEXT, (long)0, IPC_NOWAIT) == -1) {
     return 3;
   }
   printf ("%d %s\n", mdata.mtype, mdata.mtext);
 }
 else if (argc == 3) { // get assign type
   type = atol (argv[2]);
   if (msgrcv(msgid,(void *)&mdata, MAX_TEXT, type, IPC_NOWAIT) == -1) {
     return 4;
   }
   printf ("%ld %s\n", mdata.mtype, mdata.mtext);
 }
 else if (argc == 4) { // send assign type, data
   mdata.mtype = atol(argv[2]);
   strcpy (mdata.mtext, argv[3]);
   mdata.mtext[strlen(mdata.mtext)] = '\0';
   if (msgsnd (msgid, (void *)&mdata, MAX_TEXT, IPC_NOWAIT) == -1 ) {
     return 5;
   }
   printf ("send to msg_id %d with type %ld : '%s'\n", msgid, (long)mdata.mtype, mdata.mtext);
 }
 return 0;
} // end of main()