hid_map_usage(9)

💅 hid_map_usage(9) — like, the Kernel API Manual page, bestie ✨

okay so picture this: you're deep in the kernel, you've got a struct hid_input * in one hand and a struct hid_usage * in the other, and you just need somebody to map that usage to the right input bits. that somebody is hid_map_usage. she's the plug. she's iconic. let's get into it 🎀

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🌸 NAME 🌸

hid_map_usage — map usage input bits (yes literally that's the whole job and she does it flawlessly, no cap)

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✨ SYNOPSIS ✨

void hid_map_usage (struct hid_input *hidinput , struct hid_usage *usage
, unsigned long **bit , int *max , __u8 type , unsigned int c );

like, six args, all vibes, all necessary 🫶

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🦋 ARGUMENTS 🦋

• hidinput — the hidinput we're interested in 💖 like, the one you actually care about, main character energy
• usage — the usage you're gonna fill in, she's getting filled in (with data bestie, with data)
• bit — a pointer to input->{}bit — it's an out parameter, so she writes back to you, generous queen
• max — the maximal valid usage->code to consider later — also an out parameter, also coming back to you 🔥
• type — the input event type, like EV_KEY, EV_REL, ... you know the drill 🌈
• c — the code that corresponds to this usage and this type, they go together fr fr

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💜 DESCRIPTION 💜

okay so here's the tea, and it's important tea:

the value pointed to by bit will be set to NULL if either type is an unhandled event type, or if c is out of range for type. 😭

and that's not a bug bestie, that's the whole point — you can literally use that as an error condition. NULL in bit = something went sideways, go handle it. 🚨

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🧚 SEE ALSO 🧚

• Kernel file ./include/linux/hid.h — the source of truth, the mothership 📁
• HID quirks(9)
• struct hid_battery(9)
• struct hid_driver(9)
• struct hid_ll_driver(9)
• module_hid_driver(9)
• hid_device_io_start(9)
• hid_device_io_stop(9)
• hid_map_usage_clear(9)
• hid_parse(9)
• hid_hw_power(9)
• hid_hw_idle(9)
• hid_hw_may_wakeup(9)
• hid_hw_wait(9)
• hid_report_len(9)

basically the whole HID friend group, go say hi 💅✨

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and that's the page!! this one lives in ./include/linux, it's dated October 2026, and the header at the top says hid_map_usage(9) because obviously, it's her page 👑 stay hydrated, read your manpages, mwah 🍓💖