Understanding Linux Network Internals

Skeleton of NIC Registration and Unregistration

Figure 8-1(a) shows the generic scheme for an NIC's device driver to register with the networking code. Figure 8-1(b) shows the complementary action that takes place for unregistration. Although the example shows a PCI Ethernet NIC, the scheme is the same for other device types; only the name of the routine that takes care of it, or the way that routine is invoked, may change depending on how the bus code is implemented.

Figure 8-1. (a) Device registration model; (b) device unregistration model

The function starts by allocating the net_device structure with alloc_etherdev. alloc_etherdev also initializes all the parameters that are common to all Ethernet devices. The driver then initializes another portion of the net_device structure, and concludes the device registration with a call to the register_netdev routine.

Note that:

• The driver calls the appropriate wrapper around alloc_netdev (alloc_etherdev in the example), and provides only the size of its private data block. A few wrappers are listed in Table 8-1.

• The wrapper calls alloc_netdev using the parameter provided by the driver, and adds the other two (the device name and the initialization routine).

• The size of the memory block allocated by alloc_netdev includes the net_device structure, the driver's private block, and some padding to force an alignment. See Figure 8-2 later in the chapter. ...