Question

the device driver I’m working on is implementing a virtual device. The logic
is as follows:

static struct net_device_ops virt_net_ops = {
  .ndo_init = virt_net_init,
  .ndo_open = virt_net_open,
  .ndo_stop = virt_net_stop,
  .ndo_do_ioctl = virt_net_ioctl,
  .ndo_get_stats    = virt_net_get_stats,
  .ndo_start_xmit   = virt_net_start_xmit,
};

...

  struct net_device *dev;
  struct my_dev *virt;

  dev = alloc_netdev(..);
  /* check for NULL */

  virt = netdev_priv(dev);

  dev->netdev_ops = &virt_net_ops;
  SET_ETHTOOL_OPS(dev, &virt_ethtool_ops);
  dev_net_set(dev, net);
  virt->magic = MY_VIRT_DEV_MAGIC;
  ret = register_netdev(dev);
  if (ret) {
     printk("register_netdev failed\n");
     free_netdev(dev);
     return ret;
  }
...

What happens is that somewhere somehow the pointer net_device_ops in
‘net_dev’ gets corrupted, i.e.

1) create the device the first time (allocated net_dev, init the fields
including net_device_ops,which is
initialized with a static structure containing function pointers), register
the device with the kernel invoking register_netdev() – OK

2) attempt to create the device with the same name again, repeat the above
steps, call register_netdev() which will return negative and we
free_netdev(dev) and return error to the caller.

And between these two events the pointer to net_device_ops has changed,
although nowhere in the code it is done explicitly except the initialization
phase.

The kernel version is 2.6.31.8, platform MIPS. Communication channel between the user space and the kernel is implemented via netlink sockets.

Could anybody suggest what possibly can go wrong?
Appreciate any advices, thanks.

Mark

Answer 1

“The bug is somewhere else. “

The second device should not interact with the existing one. If you register_netdev with an existing name, nevertheless the ndo_init virtual function is called first before the condition is detected and -EEXIST is returned. Maybe your init function does something nasty involving some global variables. (For example, does the code assume there is one device, and stash a global pointer to it during initialization?)