usb_control_msg(9)

📦 version 7.3.1, in nixpkgs unstable

✨ usb_control_msg — Kernel API Manual, page 9 ✨

ok so like, welcome to the usb_control_msg(9) glow-up bestie 💅 this is the little kernel man page that lives over in ./drivers/usb/core and honestly? she's kind of a legend. periodt.

🌸 NAME 🌸

usb_control_msg — builds a control urb, sends it off, and waits for completion. that's it, that's the whole vibe 🎀

🦋 SYNOPSIS 🦋

int usb_control_msg (struct usb_device *dev , unsigned int pipe , __u8
request , __u8 requesttype , __u16 value , __u16 index , void *data ,
__u16 size , int timeout );

like, nine arguments. she is high-maintenance and we love her for it 🫶

💖 ARGUMENTS 💖

  • dev — pointer to the usb device you're sending the message to. the main character, fr.
  • pipe — the endpoint "pipe" you're sending the message to. it's giving delivery route.
  • request — the USB message request value.
  • requesttype — the USB message request type value.
  • value — the USB message value.
  • index — the USB message index value.
  • data — pointer to the data you're sending.
  • size — length in bytes of the data you're sending. yes, bytes. count them. 💀
  • timeout — time in msecs to wait for the message to complete before timing out.

🧚 CONTEXT 🧚

task context, might sleep. 😴 lowkey the whole tea right there.

👑 DESCRIPTION 👑

ok so what she actually does: this function sends a simple control message to a specified endpoint and then waits for the message to complete — or to time out. no cap, that's the job. ⭐

do NOT use this function from within an interrupt context. 🙈 like, seriously, don't.

if you need an asynchronous message, or you need to send a message from within interrupt context, use usb_submit_urb instead. that's the move. 💅

and if a thread in your driver uses this call, make sure your disconnect method can wait for it to complete. why? because you don't have a handle on the URB being used, so — and this is the crucial part — you can't cancel the request. 😭 no takebacks, no undo button, it's giving commitment issues but in reverse.

🌈 RETURN 🌈

  • if it's successful → the number of bytes transferred. slay. 🎀
  • otherwise → a negative error number. not slay, but informative. 😭

🍓 SEE ALSO 🍓

like, the whole friend group showed up. iykyk 💜

💖 okay that's the page!! shoutout to ./drivers/usb/core, dated October 2026 — she's serving usb realness and we are obsessed. bye bestie, go send some control messages (respectfully, not from interrupt context) 💖

📦 where this page comes from