Understanding Linux Network Internals

Updating the Device Queuing Discipline State

We saw in the section "Queuing Discipline State" which flags can be set in dev->state to define the device queuing discipline state. In this section, we will see how two of those flags are used to handle power management and link state changes.

Interactions with Power Management

When the kernel has support for power management, NIC device drivers can be notified when the system goes into suspend mode, when it is resumed, etc. We saw in the section "Example of PCI NIC Driver Registration" in Chapter 6 how the suspend and resume function pointers of the pci_driver structures are initialized depending on whether the kernel has support for power management. This is, for example, how the drivers/net/3c59x.c device driver initializes its pci_driver instance:

static struct pci_driver vortex_driver = {
    .name        "3c59x",
    .probe        vortex_init_one,
    .remove        _ _devexit_p(vortex_remove_one),
    .id_table    vortex_pci_tbl,
#ifdef CONFIG_PM
    .suspend    vortex_suspend,
    .resume        vortex_resume,
#endif
};

When the system goes into suspend mode, the suspend routines provided by device drivers are executed to let drivers take action accordingly. Power management state changes do not affect the registration status dev->reg_state, but the device state dev->state needs to be changed.

Suspending a device

When a device is suspended, its device driver handles the event, by calling, for example, the pci_driver's suspend routine for PCI devices. Besides the driver-specific actions, a ...