usb_control_msg_recv(9)

📦 version 7.3.1, in nixpkgs unstable

🌟 usb_control_msg_recv(9) 🌟

Okay bestie, gather 'round, because we're diving into the Kernel API Manual for usb_control_msg_recv(9). This one's a little function that builds a control "receive" message, sends it off, and then just… waits for it to finish. Very main character energy, honestly. 💅

🎀 SYNOPSIS 🎀

int usb_control_msg_recv (struct usb_device *dev , __u8 endpoint , __u8
request , __u8 requesttype , __u16 value , __u16 index , void
*driver_data , __u16 size , int timeout , gfp_t memflags );

✨ ARGUMENTS ✨

  • dev — pointer to the usb device to send the message to 🫶
  • endpoint — endpoint to send the message to
  • request — USB message request value
  • requesttype — USB message request type value
  • value — USB message value
  • index — USB message index value
  • driver_data — pointer to the data to be filled in by the message
  • size — length in bytes of the data to be received
  • timeout — time in msecs to wait for the message to complete before timing out ⏳
  • memflags — the flags for memory allocation for buffers

🌈 CONTEXT 🌈

!in_interrupt ()

💖 DESCRIPTION 💖

So, this function sends a control message to a specified endpoint that's expected to fill in a response (basically a "receive message" vibe) and then it waits for the message to complete, or for the timeout to hit. It's giving patient, but with boundaries. ✨

🚨 Do NOT use this function from within an interrupt context. Like, periodt. If you need an asynchronous message, or you need to send a message from within an interrupt context, use usb_submit_urb. And if a thread in your driver uses this call, make sure your disconnect method can wait for it to complete. Because — and this is lowkey important — since you don't have a handle on the URB used, you can't cancel the request. No cap. 😭

The data pointer can be made to a reference on the stack, or anywhere else that can be successfully written to. This function does not have the restriction that usb_control_msg has, where the data pointer must be to dynamically allocated memory (i.e. memory that can be successfully DMAed to a device). So that's a slay for stack babies. 💅

The "whole" message must be properly received from the device in order for this function to be successful. If a device returns less than the expected amount of data, then the function will fail. So do not use this for messages where a variable amount of data might be returned. It's all-or-nothing, iykyk. 🔥

⭐ RETURN ⭐

If successful, 0 is returned. Otherwise, a negative error number. Simple as that, bestie. 💀

👑 SEE ALSO 👑

And that's the whole vibe check, bestie! This page comes straight from ./drivers/usb/core, dated October 2026, and it's the usb_control_msg_recv(9) manual page. Go forth and receive those messages responsibly. 🦋💜

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