STRUCT USB_INTERFACE_CACHE(9)

📦 version 7.3.1, in nixpkgs unstable

✨ struct usb_interface_cache(9) ✨

okay so bestie, we're in the Kernel API Manual today and this one is genuinely one of the good ones — it's the long-term representation of a device interface 💅 like, this struct is the one that stays.

🌸 NAME 🌸

struct usb_interface_cache — long-term representation of a device interface ✨

🦋 SYNOPSIS 🦋

struct usb_interface_cache {
    unsigned num_altsetting;
    struct kref ref;
    struct usb_host_interface altsetting[];
 };

🎀 Members 🎀

  • num_altsetting — the number of altsettings that are defined, fr fr. that's the count, no cap.
  • ref — the reference counter 🫶 (it's a struct kref, she's keeping track).
  • altsetting — a variable-length array of interface structures, one for each alternate setting that may be selected ✨. each one includes a set of endpoint configurations. and heads up: they will be in no particular order 🙈 so don't go assuming any kind of sorted vibe, because there isn't one.

💖 Description 💖

so here's the moment. these structures persist for the lifetime of a usb_device — which is literally the whole point of them. unlike struct usb_interface (which persists only as long as its configuration is installed 😭), these ones stick around.

and because they stick around, the altsetting arrays can be accessed through these structures at any time ⭐ — that means you can compare configurations, and it's also what provides support for the /sys/kernel/debug/usb/devices pseudo-file. icon behaviour. ate. 👑

🌈 SEE ALSO 🌈

kernel file ./include/linux/usb.h, plus the whole friend group:

okay that's the whole page bestie, go forth and cache responsibly 🧚💜

this one came out of ./include/linux and it's dated October 2026 — and the page footer is still signing off as struct usb_interface_cache(9), periodt 💅🍓
📦 where this page comes from