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 4.8.                 January 2017                   STRUCT USB_HOST_CONF(9)