Python3以阻塞模式读取字符设备

Question

I wrote a character device driver. Now I want to use python to read from it when there is data. However, I found that the modules "io" as well as "os" do not block upon reading. The latter even when I set os.set_blocking(fd,true).

Is there a way to access the device in blocking mode? Or do I miss something in the device driver (tail works fine)?

f=io.open("/dev/tstty0","r")
while (1)
  data=str(f.read(32))
  print("mark") # <--- endless list of marks
  #do somthing

The read function of the device driver:

static ssize_t tstty_read(
  struct file *filp,
  char *buffer,
  size_t length,
  loff_t *offset)
{
  unsigned char b;
  unsigned long ofs=0;
  devConfig* dev=filp->private_data;
  if (dev)
  {
    while (fifoGet(&dev->tcp2dev,&b) && (ofs<length))
    {
      if (put_user(b,buffer+ofs))
      {
        printk(KERN_ERR "Could not copy user data");
        return -EINVAL;
      }
      ofs++;
    }
    //printk(KERN_INFO "Reading device");
    return ofs;
  }
  printk(KERN_ERR "Unknown device: %s",filp->f_path.dentry->d_iname);
  return -EINVAL;
};

The read function reads any bytes available from a fifo. I none is available 0 is returned.

Answer 1

Kudos to Ian Abbott. A character device has to implement the ability to block a read request. The read file operation has to evaluate filp->f_flags & O_NONBLOCK to check if a client has requested blocking I/O.

This link helped me with an example: simple linux driver code for blocking and non-blocking read

This example works but one has to consider two more things not covered in the example: a) What to do when you want to unload the driver while in read operation (just dont do it or wake up and abort)? b) How to abort a client caught in blocking I/O?