I am currently working on an application for my master thesis that does transparent inline modification of frames received from a uvc webcam which are served to the actual host through a uvc gadget mimicking the underlying webcam. I recently noticed that the host side v4l2 driver would only ever request bFrameIndex 1, no matter the requested format. So I used usbmon to take a closer look (pcap is attached ). Take a look at the Video Streaming interface descriptor in packet no. 6: All 19 different framesizes have their bFrameIndex set to 1. This makes requesting any framesize but the actual first one impossible. I took a quick look at drivers/usb/gadget/function/uvc_configfs.c and noticed that the bFrameIndex attribute of a frame is set to 1 per default in "uvcg_frame_make"**, but the attribute is neither made accessible through configfs nor could I see any mechanism by which the indices are set automatically. As I am new to kernel development, I wanted ask for comment first before I start brewing up a possible patch for this bug. Currently I see three solutions: 1) Expose bFrameIndex through ConfigFs, to be set by the user 2) Assign an unused bFrameIndex during "uvcg_frame_make" 3) Once framesizes of a format are finalized, iterate through frames and assign ascending indices There is also obviously the possibility that I gravely misconfigured my gadget through configfs, if so please point me in the right direction. Regards, Joel
Attachment:
bFrameIndex_bug.pcapng
Description: application/pcapng
