Understanding Linux Network Internals

Device Unregistration

To unregister a device, the kernel and the associated device driver need to undo all the operations that were executed during its registration, and more:

• Disable the device with dev_close, described in the section "Enabling and Disabling a Network Device."

• Release all the allocated resources (IRQ, I/O memory, I/O port, etc.)

• Remove the net_device structure from the global list dev_base and the two hash tables introduced in the section "Organization of net_device Structures."

• Once all the references to the structure have been released, free the net_device data structure, the driver's private data structure, and any other memory block linked to it (see Figure 8-2). The net_device structure is freed with free_netdev. When the kernel is compiled with support for sysfs, free_netdev lets it take care of freeing the structure.

• Remove any file that may have been added to the /proc and /sys filesystems.

Note that whenever there is a dependency between devices, unregistering one of them may force the unregistration of all (or part) of the others. See the section "Virtual Devices" for an example.

Three function pointers in net_device (represented by a variable named dev) come into the picture when unregistering a device:

dev->stop

This function pointer is initialized by the device driver to one of its local routines. It is invoked by dev_stop when disabling a device (see the section "Enabling and Disabling a Network Device"). Common tasks handled here include stopping the egress ...