以下是修改后的代码：
```c
#include
#include
#include
#include
#include
void show_msg(int msgid);
int main(int argc, char **argv) {
key_t mkey;
int msg_id;
if (argc != 2) {
fprintf(stderr, "usage: showing keyval \n");
exit(1);
}
mkey = (key_t) atoi(argv[1]);
if ((msg_id = msgget(mkey, 0)) == -1) {
perror("msgget failed");
exit(2);
}
show_msg(msg_id);
exit(0);
}
void show_msg(int msgid) {
struct msqid_ds buf;
if (msgctl(msgid, IPC_STAT, &buf) == -1) {
perror("msgctl");
exit(EXIT_FAILURE);
}
printf("Message queue owner UID: %d\n", buf.msg_perm.uid);
printf("Message queue owner GID: %d\n", buf.msg_perm.gid);
printf("Message queue access permissions: %#o\n", buf.msg_perm.mode);
printf("\n");
printf("Key: %d\n", buf.msg_perm.__key);
printf("Number of messages on queue: %ld\n", buf.msg_qnum);
printf("Maximum number of bytes allowed on queue: %ld\n", buf.msg_qbytes);
printf("PID of last msgsnd: %d\n", buf.msg_lspid);
printf("PID of last msgrcv: %d\n", buf.msg_lrpid);
printf("Time of last msgsnd: %s", ctime(&buf.msg_stime));
printf("Time of last msgrcv: %s", ctime(&buf.msg_rtime));
printf("Time of last change: %s", ctime(&buf.msg_ctime));
}
```
在原有的基础上，我们添加了一个新的函数show_msg来打印消息队列的所有者和权限。同时，我们也将mqstat_print函数重命名为show_msg，并对其进行了修改，使其能够打印出更多的消息队列信息。
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