usb_string(9)

💖 usb_string — bestie's guide to the UTF-8 glow-up 💖

okay so this is a page from the Kernel API Manual, and it's all about usb_string(9) — your little bestie for turning cursed device strings into something a kernel dev can actually read. no cap, it's lowkey iconic.

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✨ SYNOPSIS ✨

int usb_string (struct usb_device *dev , int index , char *buf , size_t
size );

like… that's the whole spell. feed it four things and out comes a string (or a sad negative number, we'll get there 🫶).

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🎀 ARGUMENTS 🎀

• dev — the device whose string descriptor is being retrieved. literally the device, the main character, the one holding the string you want 💅
• index — the number of the descriptor. think of it as the seat number in the string-descriptor theatre.
• buf — where to put the string. your little output basket 🧺
• size — how big is "buf"? yes, the manpage really does put "buf" in quotes, we love a sassy rhetorical question. this is your buffer's capacity, don't overshoot it.

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🌸 CONTEXT 🌸

task context, might sleep. 😴 translation: do NOT call this from an interrupt context, bestie. it will nap on you, and you'll have a bad time.

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🦋 DESCRIPTION 🦋

Okay so here's the tea 🍓: devices hand back strings encoded as UTF-16LE from usb_get_string_descriptor, and that is… not it for most kernel contexts. this function converts them into null-terminated UTF-8 encoded ones, which are infinitely more usable in most kernel contexts. glow-up complete, periodt. ✨

Not me needing to warn you about one thing though: this function chooses strings in the first language supported by the device. so if your device speaks multiple languages, you get the first one, and that's just how it is. 🙈

This call is synchronous, and may not be used in an interrupt context. (yes, we said that in CONTEXT too — it's that serious. no interrupt-context shenanigans. 💀)

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🔥 RETURN 🔥

• length of the string (>= 0) — slay, you got your string 🌈
• or usb_control_msg status (< 0) — the vibe check failed, go read that status 😭

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👑 SEE ALSO 👑

Kernel file ./drivers/usb/core/message.c plus this whole friend group of USB functions:

• usb_control_msg(9)
• usb_control_msg_send(9)
• usb_control_msg_recv(9)
• usb_interrupt_msg(9)
• usb_bulk_msg(9)
• usb_bulk_msg_killable(9)
• usb_sg_init(9)
• usb_sg_wait(9)
• usb_sg_cancel(9)
• usb_get_descriptor(9)
• usb_get_string(9)
• usb_cache_string(9)
• usb_get_status(9)
• usb_clear_halt(9)
• usb_disable_endpoint(9)
• usb_reset_endpoint(9)
• usb_disable_interface(9)
• usb_disable_device(9)
• usb_enable_endpoint(9)
• usb_enable_interface(9)
• usb_set_interface(9)
• usb_reset_configuration(9)
• usb_set_wireless_status(9)
• usb_driver_set_configuration(9)
• cdc_parse_cdc_header(9)

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🫶 quick reminder before you go: the synopsis is int usb_string (struct usb_device *dev , int index , char *buf , size_t size ); — same bytes, same vibes, don't let anyone tell you otherwise.

💜 mwah, that's the page! it lives in ./drivers/usb/core, it's dated October 2026, and it goes by usb_string(9) — see you in the kernel, bestie! 🧚🎀