15_1msgctl的使用

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

//IPC對象；消息隊列是linux內核給你持久化(我們可以從linux內核中獲取消息隊列的信息,修改消息隊列)
/*

      The msqid_ds data structure is defined in <sys/msg.h> as follows:
//設置或返回消息隊列的信息,存在於用戶空間
           struct msqid_ds {
               struct ipc_perm msg_perm;     // Ownership and permissions 
               time_t          msg_stime;    // Time of last msgsnd(2) 
               time_t          msg_rtime;    // Time of last msgrcv(2)
               time_t          msg_ctime;    // Time of last change 
               unsigned long   __msg_cbytes; // Current number of bytes in
                                              // queue (nonstandard) 
               msgqnum_t       msg_qnum;     // Current number of messages
                                             // in queue 
               msglen_t        msg_qbytes;   // Maximum number of bytes
                                              / allowed in queue 
               pid_t           msg_lspid;    // PID of last msgsnd(2) 
               pid_t           msg_lrpid;    // PID of last msgrcv(2)
           };

       The ipc_perm structure is defined as follows (the highlighted fields are  settable  using
       IPC_SET):

           struct ipc_perm {
               key_t          __key;       // Key supplied to msgget(2) 
               uid_t          uid;         // Effective UID of owner
               gid_t          gid;         // Effective GID of owner
               uid_t          cuid;        // Effective UID of creator 
               gid_t          cgid;        // Effective GID of creator
               unsigned short mode;        // Permissions 
               unsigned short __seq;       // Sequence number 
           };
*/

//通過msqid刪除消息隊列 ipcrm -q msqid
/*
	
	//可發送的最長消息字節數
	hzmct@U-64:~$ cat /proc/sys/kernel/msgmax 
	8192
	
	//一個特定隊列的最大字節數(這個隊列中所有的消息長度之和)
	hzmct@U-64:~$ cat /proc/sys/kernel/msgmnb 
	16384
	
	//系統中的最大消息數
	hzmct@U-64:~$ cat /proc/sys/kernel/msgmni
	32000

*/
void showq(void * buf)
{
	if(buf == NULL)
	{
		printf("buf == NULL ");
		return;	
	}
	
	struct msqid_ds *msqid_ds = (struct msqid_ds *)buf;
	printf("************************show ipc msgq************************\n");
	printf("該消息隊列對應的鍵:%x\n", msqid_ds->msg_perm.__key);
	printf("該消息隊列訪問權限:%o\n", msqid_ds->msg_perm.mode);
	printf("該消息隊列的序號:%d\n", msqid_ds->msg_perm.__seq);
	
	printf("該消息隊列 UID of owner:%d\n", msqid_ds->msg_perm.uid);
	printf("該消息隊列 GID of owner:%d\n", msqid_ds->msg_perm.gid);
	printf("該消息隊列 UID of creator:%d\n", msqid_ds->msg_perm.cuid);
	printf("該消息隊列 GID of creator:%d\n", msqid_ds->msg_perm.cgid);
	
	
	printf("消息隊列中的消息個數:%d\n", (int)msqid_ds->msg_qnum);
	printf("當前消息隊列中有多少字節:%ld\n", (long int)msqid_ds->__msg_cbytes);
	
	printf("該消息最後發送的時間:%ld, 進程id:%d\n", (long int)msqid_ds->msg_stime, msqid_ds->msg_lspid);
	printf("該消息最後接收的時間:%ld, 進程id:%d\n", (long int)msqid_ds->msg_rtime, msqid_ds->msg_lrpid);
	printf("接收該消息的修改時間:%ld\n", (long int)msqid_ds->msg_ctime);
	printf("消息隊列所有消息之和最大字節數(取決於系統):%d\n", (int)msqid_ds->msg_qbytes);
}

//IPC_STAT 獲取消息隊列信息
#if 0
int test()
{
	int msgid;
	int ret;
	msgid = msgget(0x1234, 0666|IPC_CREAT);
	if (msgid == -1) 
	{
		if (errno == ENOENT) 
		{
			printf("自己檢查錯誤, 消息隊列不存在\n");
		}
		perror("msgget");
		return -1;
	}
	printf("msgid:%d\n", msgid);
	printf("創建消息隊列成功\n");
	
	struct msqid_ds buf;
	memset(&buf, 0, sizeof(struct msqid_ds));
	//獲取隊列狀態
	ret = msgctl(msgid, IPC_STAT, &buf);
	if (ret == -1) 
	{
		perror("mdgctl");
	}
	showq(&buf);
	return 0;
}
#endif

//IPC_SET 設置消息隊列信息（先獲取在設置）
#if 1
int test()
{
	int msgid;
	int ret;
	msgid = msgget(0x1234, 0666|IPC_CREAT);
	if (msgid == -1) 
	{
		if (errno == ENOENT) 
		{
			printf("自己檢查錯誤, 消息隊列不存在\n");
		}
		
		if (errno == EACCES) 
		{
			printf("自己檢查錯誤, 用戶進程沒有權限訪問\n");
		}
		
		perror("msgget");
		return -1;
	}
	printf("msgid:%d\n", msgid);
	printf("創建消息隊列成功\n");
	
	struct msqid_ds buf;
	memset(&buf, 0, sizeof(struct msqid_ds));
	//獲取隊列狀態
	ret = msgctl(msgid, IPC_STAT, &buf);
	if (ret == -1) 
	{
		perror("獲取消息隊列狀態");
	}
	
	//修改消息隊列的訪問模式權限
	buf.msg_perm.mode = 0444;
	ret = msgctl(msgid, IPC_SET, &buf);
	if (ret == -1) 
	{
		perror("修改消息隊列");
	}
	
	showq(&buf);
	//刪除消息隊列
	ret = msgctl(msgid, IPC_RMID, &buf);
	if (ret == -1) 
	{
		perror("刪除消息隊列");
	}
	
	return 0;
}
#endif
int main()
{
	test();
	return 0;
}

運行結果：