usb_fill_control_urb(9)

💅 usb_fill_control_urb(9) — the Kernel API Manual, bestie edition 🎀

Okay so this is a page straight out of the Kernel API Manual, and it's about usb_fill_control_urb — the little glow-up routine that gets a control urb ready to go out into the world. Let's get into it ✨

🌸 NAME 🌸

usb_fill_control_urb — initializes a control urb, periodt 💅

🦋 SYNOPSIS 🦋

void usb_fill_control_urb (struct urb *urb , struct usb_device *dev ,
unsigned int pipe , unsigned char *setup_packet , void *transfer_buffer
, int buffer_length , usb_complete_t complete_fn , void *context );

✨ ARGUMENTS ✨

• urb — pointer to the urb you're about to initialize. yep, that one 🫶
• dev — pointer to the struct usb_device for this urb.
• pipe — the endpoint pipe.
• setup_packet — pointer to the setup_packet buffer. ⚠️ heads up: the buffer must be suitable for DMA.
• transfer_buffer — pointer to the transfer buffer. also must be suitable for DMA, no exceptions 💀
• buffer_length — length of the transfer buffer.
• complete_fn — pointer to the usb_complete_t function.
• context — what to set the urb context to.

🔥 DESCRIPTION 🔥

So what does it do? It initializes a control urb with all the proper information needed to submit it to a device. That's the whole gig, and it ate 💅

Now the part you actually need to internalize, bestie: the transfer buffer and the setup_packet buffer will most likely be filled or read via DMA. The simplest way to get a buffer that can be DMAed to is allocating it via kmalloc or equivalent — even for very small buffers. Like, don't get cute about it, just kmalloc it 🎀

If the buffers are embedded in a bigger structure, there is a risk that the buffer itself, the previous fields and/or the next fields are corrupted due to cache incoherencies — or slowed down if they are evicted from the cache. Not a vibe 😭

For more information, check struct urb. iykyk 💖

🌈 SEE ALSO 🌈

Kernel file ./include/linux/usb.h — plus the whole squad, and yes we're listing every single one of them, no cap 👑

• struct usb_host_endpoint(9)
• struct usb_interface(9)
• usb_set_intfdata(9)
• struct usb_interface_cache(9)
• struct usb_host_config(9)
• struct usb_device(9)
• usb_hub_for_each_child(9)
• usb_interface_claimed(9)
• usb_make_path(9)
• USB_DEVICE(9)
• USB_DEVICE_VER(9)
• USB_DEVICE_INTERFACE_CLASS(9)
• USB_DEVICE_INTERFACE_PROTOCOL(9)
• USB_DEVICE_INTERFACE_NUMBER(9)
• USB_DEVICE_INFO(9)
• USB_INTERFACE_INFO(9)
• USB_DEVICE_AND_INTERFACE_INFO(9)
• USB_VENDOR_AND_INTERFACE_INFO(9)
• struct usb_driver(9)
• struct usb_device_driver(9)
• struct usb_class_driver(9)
• module_usb_driver(9)
• struct urb(9)
• usb_fill_bulk_urb(9)
• usb_fill_int_urb(9)
• usb_urb_dir_in(9)
• usb_urb_dir_out(9)
• struct usb_sg_request(9)

And that's the whole page, bestie 🫶 This lil icon comes to you from ./include/linux, dated October 2026, living in the Kernel API Manual — go forth and DMA responsibly 🧚💜