STRUCT USB_HOST_CONFIG(9)

📦 version 7.3.1, in nixpkgs unstable

💅 struct usb_host_config(9) — like, the whole Kernel API Manual, but make it make sense

okay so bestie, welcome to the kernel API manual page for struct usb_host_config ✨ this is the glow-up version, and yes, every single detail is still here because I would never do you dirty like that 🫶

✨ NAME ✨

struct usb_host_config — it's the representation of a device's configuration, periodt 💅

🌸 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;
 };

like literally that's the whole struct, no notes 🔥

🎀 Members 🎀

okay so let's meet the cast, they all have main character energy in their own way:

  • desc — the device's configuration descriptor, the blueprint of it all 💖
  • string — pointer to the cached version of the iConfiguration string, if it's present for this configuration (no string, no pointer, that's the vibe) 🌸
  • intf_assoc — list of any interface association descriptors in this config 🦋
  • interface — array of pointers to usb_interface structures, one for each interface in the configuration. The number of interfaces is stored in desc.bNumInterfaces. big warning bestie: these pointers are valid only while the configuration is active 👑
  • intf_cache — 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 — immortal icons fr fr ⭐
  • extra — pointer to the buffer containing all extra descriptors associated with this configuration (those preceding the first interface descriptor) 💜
  • extralen — the length of the extra descriptors buffer, the receipts 🧚

💀 Description 💀

USB devices may have multiple configurations, but bestie, only one can be active at any time. No sharing, no multitasking, it's giving exclusivity 💅 Each configuration 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, and each one corresponds to a different function of the USB device. All of them are available whenever the configuration is active. Slay, multitasking device 🌈

Now, the USB standard says interfaces are supposed to be numbered from 0 to desc.bNumInterfaces-1, but a lot of devices get this wrong 🙈 not them being messy. In addition, the interface array is not guaranteed to be sorted in numerical order. So don't just vibe-check by index — use usb_ifnum_to_if to look up an interface entry based on its number. iykyk 🔥

okay so important one: device drivers should not attempt to activate configurations. The choice of which configuration to install is a policy decision based on things like available power, functionality provided, and the user's desires (expressed through userspace tools). So like, stay in your lane, driver 💀

However — plot twist — drivers can call usb_reset_configuration to reinitialize the current configuration and all its interfaces. That one's allowed, go off 🫶

🦋 SEE ALSO 🦋

the whole friend group, no one gets left out:

and that's the page bestie! 🎀 this little masterpiece lives at ./include/linux, dated October 2026, and it's signed off as struct usb_host_config(9) from the Kernel API Manual 💖 go read some source, ily, bye! 💅✨

📦 where this page comes from