信号量的测试问题！

发布于 2022-09-18 18:33:10 字数 5334 浏览 11 评论 0

程序的意图测试信号量（一个进程想要获得已经被另一个进程持有的信号量时，该进程应该要挂起，加入到该信号量的等待队列中，当信号量释放后，唤醒进程加入到调度器中运行。）
下面的驱动故意做了一下修改：就是要看程序出现以上的现象。
故意在驱动write中不把信号量释放,让当子进程read时,应该是要挂起的!
可是并没有挂起,而是把数据读出来了,程序顺利的完成了,就像没有正常的一样!如果把子进程read改成write时,就可以.这为什么?是不是fork()的原因?
前辈给指教一下!
以下为DOME：
#include <stdio.>
#include <fcntl.h>
#include <unistd.h>
#define  DEV_NAME "/dev/signel"
int main()
{ int fd,ret,arry;
  arry=100;
  fd=open(DEV_NAME,O_WRONLY);
  if(fd<0)
    { printf("the file is opened to fail!!&fd=%d\n",fd);
       }
  else
    { printf("the file is opened to scuss!!&fd=%d\n",fd);
   printf("the data(arry)=%d will is writing in driver\n",arry);
   write(fd,&arry,sizeof(arry));  /*当此处获得信号量，末释放，下面的进程来访问共享资源时，进程被挂起*/
   if(fork()==0)
      { read(fd,&arry,sizeof(arry));
      printf("read got the data---arry=%d\n",arry);
   exit(0);
         }
       }
  ret=close(fd);
  if(ret<0)
    { printf("the file is closed to fail!!&ret=%d\n",ret);
       }
  else
    { printf("the file is close to scuss!!&ret=%d\n",ret);
   }
  exit(1);
  }

以下为驱动：
#define  DEV_NAME  "signel"
#define  DEV_ID 110
struct signel {
static int arry;
struct semaphore sem;
}signel_buff;
static int signel_write(struct file *file,const char __user * buf,size_t count,loff_t *off)
{ printk("%i,%s\n",current->pid,current->comm);
  if(down_interruptible(&signel_buff.sem))
       { return -ERESTARTSYS;
          }
  printk("write data....!!!\n");
  if(copy_from_user(&signel_buff.arry,buf,count))
    { up(&signel_buff.sem);
   return -EFAULT;
       }
  up(&signel_buff.sem);  当数据写完,故意把这条语句删了(不释放信号量)!就是要检测信号量挂起的目的.
  return count;
}
static int signel_read(struct file *file,char __user * buf,size_t count,loff_t *off)
{  printk ("%i,%s\n",current->pid,current->comm);
if(down_interruptible(&signel_buff.sem))
{ return -ERESTARTSYS;
      }
flags=0;
printk("read data....!!!\n");
if(copy_to_user(buf,&signel_buff.arry,count))
   { up(&signel_buff.sem);
   return  -EFAULT;
      }
up(&signel_buff.sem);
return count;
}
static struct file_operations signel_test = {
.write = signel_write,
.read = signel_read,
};
static int __init init_signel(void)
{ int ret;
  sema_init(&signel_buff.sem,1);
  ret=register_chrdev(DEV_ID,DEV_NAME,&signel_test);
  if(ret<0)
    { printk("registre is fail!!\n");
   return ret;
      }
else
   { printk("registre is scuss!!\n");
   devfs_mk_cdev(MKDEV(DEV_ID,0),S_IFCHR | S_IRUSR | S_IWUSR,"signel");
   return 0;
         }
return 0;
   }
static void __exit exit_signel(void)
{ unregister_chrdev(DEV_ID,DEV_NAME);
  devfs_remove(DEV_NAME);
   }
module_init(init_signel);
module_exit(exit_signel);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("KANG");
MODULE_DESCRIPTION("SIGNE");