STRUCT 
USB_HOST_CONF(9) 				  Host-Side Data Types and Macro				   STRUCT USB_HOST_CONF(9)

NAME

       struct_usb_host_config - representation of a device's configuration

SYNOPSIS

       struct usb_host_config {
	 struct usb_config_descriptor desc;
	 char * string;
	 struct usb_interface_assoc_descriptor * intf_assoc[USB_MAXIADS];
	 struct usb_interface * interface[USB_MAXINTERFACES];
	 struct usb_interface_cache * intf_cache[USB_MAXINTERFACES];
	 unsigned char * extra;
	 int extralen;
       };

MEMBERS

       desc
	   the device's configuration descriptor.

       string
	   pointer to the cached version of the iConfiguration string, if present for this configuration.

       intf_assoc[USB_MAXIADS]
	   list of any interface association descriptors in this config

       interface[USB_MAXINTERFACES]
	   array of pointers to usb_interface structures, one for each interface in the configuration. The number of interfaces is stored in
	   desc.bNumInterfaces. These pointers are valid only while the the configuration is active.

       intf_cache[USB_MAXINTERFACES]
	   array of pointers to usb_interface_cache structures, one for each interface in the configuration. These structures exist for the entire
	   life of the device.

       extra
	   pointer to buffer containing all extra descriptors associated with this configuration (those preceding the first interface descriptor).

       extralen
	   length of the extra descriptors buffer.

DESCRIPTION

       USB devices may have multiple configurations, but only one can be active at any time. Each encapsulates a different operational
       environment; for example, a dual-speed device would have separate configurations for full-speed and high-speed operation. The number of
       configurations available is stored in the device descriptor as bNumConfigurations.

       A configuration can contain multiple interfaces. Each corresponds to a different function of the USB device, and all are available whenever
       the configuration is active. The USB standard says that interfaces are supposed to be numbered from 0 to desc.bNumInterfaces-1, but a lot
       of devices get this wrong. In addition, the interface array is not guaranteed to be sorted in numerical order. Use usb_ifnum_to_if to look
       up an interface entry based on its number.

       Device drivers should not attempt to activate configurations. The choice of which configuration to install is a policy decision based on
       such considerations as available power, functionality provided, and the user's desires (expressed through userspace tools). However,
       drivers can call usb_reset_configuration to reinitialize the current configuration and all its interfaces.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						   STRUCT USB_HOST_CONF(9)