lesavka/server/src/bin/lesavka-uvc.real.inc

// lesavka-uvc - minimal UVC control handler for the gadget node.

use anyhow::{Context, Result};
use std::env;
use std::fs::{File, OpenOptions};
use std::os::unix::fs::OpenOptionsExt;
use std::os::unix::io::AsRawFd;
use std::thread;
use std::time::Duration;

const STREAM_CTRL_SIZE_11: usize = 26;
const STREAM_CTRL_SIZE_15: usize = 34;
const STREAM_CTRL_SIZE_MAX: usize = STREAM_CTRL_SIZE_15;
const UVC_DATA_SIZE: usize = 60;

const V4L2_EVENT_PRIVATE_START: u32 = 0x0800_0000;
const UVC_EVENT_CONNECT: u32 = V4L2_EVENT_PRIVATE_START;
const UVC_EVENT_DISCONNECT: u32 = V4L2_EVENT_PRIVATE_START + 1;
const UVC_EVENT_STREAMON: u32 = V4L2_EVENT_PRIVATE_START + 2;
const UVC_EVENT_STREAMOFF: u32 = V4L2_EVENT_PRIVATE_START + 3;
const UVC_EVENT_SETUP: u32 = V4L2_EVENT_PRIVATE_START + 4;
const UVC_EVENT_DATA: u32 = V4L2_EVENT_PRIVATE_START + 5;

const UVC_STRING_CONTROL_IDX: u8 = 0;
const UVC_STRING_STREAMING_IDX: u8 = 1;

const CONFIGFS_UVC_BASE: &str = "/sys/kernel/config/usb_gadget/lesavka/functions/uvc.usb0";

const USB_DIR_IN: u8 = 0x80;

const UVC_SET_CUR: u8 = 0x01;
const UVC_GET_CUR: u8 = 0x81;
const UVC_GET_MIN: u8 = 0x82;
const UVC_GET_MAX: u8 = 0x83;
const UVC_GET_RES: u8 = 0x84;
const UVC_GET_LEN: u8 = 0x85;
const UVC_GET_INFO: u8 = 0x86;
const UVC_GET_DEF: u8 = 0x87;

const UVC_VS_PROBE_CONTROL: u8 = 0x01;
const UVC_VS_COMMIT_CONTROL: u8 = 0x02;
const UVC_VC_REQUEST_ERROR_CODE_CONTROL: u8 = 0x02;

#[repr(C)]
struct V4l2EventSubscription {
    type_: u32,
    id: u32,
    flags: u32,
    reserved: [u32; 5],
}

#[repr(C)]
union V4l2EventUnion {
    data: [u8; 64],
    _align: u64,
}

#[repr(C)]
struct V4l2Event {
    type_: u32,
    u: V4l2EventUnion,
    pending: u32,
    sequence: u32,
    timestamp: libc::timespec,
    id: u32,
    reserved: [u32; 8],
}

#[repr(C)]
#[derive(Clone, Copy)]
struct UsbCtrlRequest {
    b_request_type: u8,
    b_request: u8,
    w_value: u16,
    w_index: u16,
    w_length: u16,
}

#[repr(C)]
#[derive(Clone, Copy)]
struct UvcRequestData {
    length: i32,
    data: [u8; UVC_DATA_SIZE],
}

#[derive(Clone, Copy)]
struct UvcConfig {
    width: u32,
    height: u32,
    fps: u32,
    interval: u32,
    max_packet: u32,
    frame_size: u32,
}

struct PayloadCap {
    limit: u32,
    pct: u32,
    source: &'static str,
    periodic_dw: Option<u32>,
    non_periodic_dw: Option<u32>,
}

struct UvcState {
    cfg: UvcConfig,
    ctrl_len: usize,
    default: [u8; STREAM_CTRL_SIZE_MAX],
    probe: [u8; STREAM_CTRL_SIZE_MAX],
    commit: [u8; STREAM_CTRL_SIZE_MAX],
    cfg_snapshot: Option<ConfigfsSnapshot>,
}

#[derive(Clone, Copy)]
struct PendingRequest {
    interface: u8,
    selector: u8,
    expected_len: usize,
}

#[derive(Clone, Copy)]
struct UvcInterfaces {
    control: u8,
    streaming: u8,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
struct ConfigfsSnapshot {
    width: u32,
    height: u32,
    default_interval: u32,
    frame_interval: u32,
    maxpacket: u32,
    maxburst: u32,
}

fn main() -> Result<()> {
    let (dev, cfg) = parse_args()?;
    let _singleton = acquire_singleton_lock()?;
    let interfaces = load_interfaces();
    eprintln!("[lesavka-uvc] starting (dev={dev})");
    eprintln!(
        "[lesavka-uvc] interfaces control={} streaming={}",
        interfaces.control, interfaces.streaming
    );

    let debug = env::var("LESAVKA_UVC_DEBUG").is_ok();
    let nonblock = env::var("LESAVKA_UVC_BLOCKING").is_err();
    eprintln!("[lesavka-uvc] nonblock={}", if nonblock { 1 } else { 0 });
    let mut setup_seen: u64 = 0;
    let mut data_seen: u64 = 0;
    let mut dq_err_seen: u64 = 0;
    let mut dq_err_last: Option<i32> = None;

    loop {
        let file = match open_with_retry(&dev) {
            Ok(file) => file,
            Err(err) => {
                eprintln!("[lesavka-uvc] open failed: {err:#}");
                thread::sleep(Duration::from_millis(250));
                continue;
            }
        };
        let fd = file.as_raw_fd();
        let vidioc_subscribe = ioctl_write::<V4l2EventSubscription>(b'V', 90);
        let vidioc_dqevent = ioctl_read::<V4l2Event>(b'V', 89);
        let uvc_send_response = ioctl_write::<UvcRequestData>(b'U', 1);

        if let Err(err) = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_SETUP)
            .and_then(|_| subscribe_event(fd, vidioc_subscribe, UVC_EVENT_DATA))
        {
            if should_retry_uvc_error(&err) {
                eprintln!("[lesavka-uvc] subscribe failed: {err:#}");
                thread::sleep(Duration::from_millis(250));
                continue;
            }
            return Err(err);
        }
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_CONNECT).map_err(|err| {
            eprintln!("[lesavka-uvc] connect-subscribe failed: {err:#}");
        });
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_DISCONNECT).map_err(|err| {
            eprintln!("[lesavka-uvc] disconnect-subscribe failed: {err:#}");
        });
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_STREAMON).map_err(|err| {
            eprintln!("[lesavka-uvc] streamon-subscribe failed: {err:#}");
        });
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_STREAMOFF).map_err(|err| {
            eprintln!("[lesavka-uvc] streamoff-subscribe failed: {err:#}");
        });

        let mut state = UvcState::new(cfg);
        let mut pending: Option<PendingRequest> = None;

        loop {
            let mut ev = unsafe { std::mem::zeroed::<V4l2Event>() };
            let rc = unsafe { libc::ioctl(fd, vidioc_dqevent, &mut ev) };
            if rc < 0 {
                let err = std::io::Error::last_os_error();
                match err.raw_os_error() {
                    Some(libc::EAGAIN) | Some(libc::EINTR) | Some(libc::ENOENT) => {
                        if debug {
                            let code = err.raw_os_error();
                            if dq_err_seen < 10 || code != dq_err_last {
                                eprintln!("[lesavka-uvc] dqevent idle: {err}");
                                dq_err_seen += 1;
                                dq_err_last = code;
                            }
                        }
                        thread::sleep(Duration::from_millis(10));
                        continue;
                    }
                    Some(libc::ENODEV) | Some(libc::EBADF) | Some(libc::EIO) => {
                        eprintln!("[lesavka-uvc] device reset ({err}); reopening");
                        break;
                    }
                    _ => {
                        eprintln!("[lesavka-uvc] dqevent failed: {err}");
                        thread::sleep(Duration::from_millis(100));
                        continue;
                    }
                }
            }

            match ev.type_ {
                UVC_EVENT_CONNECT => {
                    let speed = u32::from_le_bytes(event_bytes(&ev)[0..4].try_into().unwrap());
                    eprintln!("[lesavka-uvc] UVC connect (speed={speed})");
                }
                UVC_EVENT_DISCONNECT => eprintln!("[lesavka-uvc] UVC disconnect"),
                UVC_EVENT_STREAMON => eprintln!("[lesavka-uvc] stream on"),
                UVC_EVENT_STREAMOFF => eprintln!("[lesavka-uvc] stream off"),
                UVC_EVENT_SETUP => {
                    let req = parse_ctrl_request(event_bytes(&ev));
                    setup_seen += 1;
                    if debug || setup_seen <= 10 {
                        eprintln!(
                            "[lesavka-uvc] setup #{setup_seen} rt=0x{:02x} rq=0x{:02x} val=0x{:04x} idx=0x{:04x} len={}",
                            req.b_request_type,
                            req.b_request,
                            req.w_value,
                            req.w_index,
                            req.w_length
                        );
                    }
                    handle_setup(
                        fd,
                        uvc_send_response,
                        &mut state,
                        &mut pending,
                        interfaces,
                        req,
                        debug,
                    );
                }
                UVC_EVENT_DATA => {
                    let data = parse_request_data(event_bytes(&ev));
                    data_seen += 1;
                    if debug || data_seen <= 10 {
                        eprintln!("[lesavka-uvc] data #{data_seen} len={}", data.length);
                    }
                    handle_data(
                        fd,
                        uvc_send_response,
                        &mut state,
                        &mut pending,
                        interfaces,
                        data,
                        debug,
                    );
                }
                _ => {
                    if debug {
                        eprintln!("[lesavka-uvc] event type=0x{:08x}", ev.type_);
                    }
                }
            }
        }
    }
}

fn should_retry_uvc_error(err: &anyhow::Error) -> bool {
    err.chain()
        .find_map(|cause| {
            cause
                .downcast_ref::<std::io::Error>()
                .and_then(|error| error.raw_os_error())
        })
        .is_some_and(|code| {
            matches!(
                code,
                libc::ENOENT | libc::ENODEV | libc::EIO | libc::EBADF | libc::EAGAIN
            )
        })
}

fn parse_args() -> Result<(String, UvcConfig)> {
    let mut args = env::args().skip(1);
    let mut dev: Option<String> = None;

    while let Some(arg) = args.next() {
        match arg.as_str() {
            "--device" | "-d" => dev = args.next(),
            _ if arg.starts_with('/') => dev = Some(arg),
            _ => {}
        }
    }

    let dev = dev
        .or_else(|| env::var("LESAVKA_UVC_DEV").ok())
        .context("missing --device (or LESAVKA_UVC_DEV)")?;

    Ok((dev, UvcConfig::from_env()))
}

impl UvcConfig {
    fn from_env() -> Self {
        let width = env_u32("LESAVKA_UVC_WIDTH", 1280);
        let height = env_u32("LESAVKA_UVC_HEIGHT", 720);
        let fps = env_u32("LESAVKA_UVC_FPS", 25).max(1);
        let interval = env_u32("LESAVKA_UVC_INTERVAL", 0);
        let mut max_packet = env_u32("LESAVKA_UVC_MAXPACKET", 1024);
        let frame_size = env_u32("LESAVKA_UVC_FRAME_SIZE", width * height * 2);
        let bulk = env::var("LESAVKA_UVC_BULK").is_ok();
        if let Some(cap) = compute_payload_cap(bulk) {
            if max_packet > cap.limit {
                eprintln!(
                    "[lesavka-uvc] payload cap {}B ({}% from {}): clamp max_packet {} -> {} (periodic_dw={:?} non_periodic_dw={:?})",
                    cap.limit,
                    cap.pct,
                    cap.source,
                    max_packet,
                    cap.limit,
                    cap.periodic_dw,
                    cap.non_periodic_dw
                );
                max_packet = cap.limit;
            } else {
                eprintln!(
                    "[lesavka-uvc] payload cap {}B ({}% from {}): max_packet {} (periodic_dw={:?} non_periodic_dw={:?})",
                    cap.limit,
                    cap.pct,
                    cap.source,
                    max_packet,
                    cap.periodic_dw,
                    cap.non_periodic_dw
                );
            }
        } else {
            eprintln!(
                "[lesavka-uvc] payload cap unavailable; using max_packet {}",
                max_packet
            );
        }
        if let Some(cfg_max) = read_u32_file(&format!("{CONFIGFS_UVC_BASE}/streaming_maxpacket")) {
            if max_packet > cfg_max {
                eprintln!(
                    "[lesavka-uvc] configfs maxpacket {}: clamp max_packet {} -> {}",
                    cfg_max, max_packet, cfg_max
                );
                max_packet = cfg_max;
            } else {
                eprintln!(
                    "[lesavka-uvc] configfs maxpacket {}: max_packet {}",
                    cfg_max, max_packet
                );
            }
        }
        if env::var("LESAVKA_UVC_BULK").is_ok() {
            max_packet = max_packet.min(512);
        } else {
            max_packet = max_packet.min(1024);
        }

        let interval = if interval == 0 {
            10_000_000 / fps
        } else {
            interval
        };

        Self {
            width,
            height,
            fps,
            interval,
            max_packet,
            frame_size,
        }
    }
}

impl UvcState {
    fn new(cfg: UvcConfig) -> Self {
        let _profile_hint = (cfg.width, cfg.height, cfg.fps);
        let ctrl_len = stream_ctrl_len();
        let default = build_streaming_control(&cfg, ctrl_len);
        Self {
            cfg,
            ctrl_len,
            default,
            probe: default,
            commit: default,
            cfg_snapshot: None,
        }
    }
}

fn load_interfaces() -> UvcInterfaces {
    let control = env_u8("LESAVKA_UVC_CTRL_INTF")
        .or_else(|| {
            read_interface(
                "/sys/kernel/config/usb_gadget/lesavka/functions/uvc.usb0/control/bInterfaceNumber",
            )
        })
        .unwrap_or(UVC_STRING_CONTROL_IDX);
    let streaming = env_u8("LESAVKA_UVC_STREAM_INTF")
        .or_else(|| read_interface("/sys/kernel/config/usb_gadget/lesavka/functions/uvc.usb0/streaming/bInterfaceNumber"))
        .unwrap_or(UVC_STRING_STREAMING_IDX);
    UvcInterfaces { control, streaming }
}

fn read_interface(path: &str) -> Option<u8> {
    std::fs::read_to_string(path)
        .ok()
        .and_then(|v| v.trim().parse::<u8>().ok())
}

fn open_with_retry(path: &str) -> Result<std::fs::File> {
    let nonblock = env::var("LESAVKA_UVC_BLOCKING").is_err();
    let read_only = uvc_control_read_only();
    for attempt in 1..=200 {
        let mut opts = OpenOptions::new();
        opts.read(true);
        if !read_only {
            opts.write(true);
        }
        if nonblock {
            opts.custom_flags(libc::O_NONBLOCK);
        }
        match opts.open(path) {
            Ok(f) => {
                let mode = if read_only { "ro" } else { "rw" };
                eprintln!("[lesavka-uvc] opened {path} mode={mode} (attempt {attempt})");
                return Ok(f);
            }
            Err(err) if err.raw_os_error() == Some(libc::ENOENT) => {
                thread::sleep(Duration::from_millis(50));
            }
            Err(err) => return Err(err).with_context(|| format!("open {path}")),
        }
    }
    Err(anyhow::anyhow!("timeout opening {path}"))
}

fn uvc_control_read_only() -> bool {
    env::var("LESAVKA_UVC_CONTROL_READ_ONLY")
        .ok()
        .map(|value| {
            let trimmed = value.trim();
            !(trimmed.eq_ignore_ascii_case("0")
                || trimmed.eq_ignore_ascii_case("false")
                || trimmed.eq_ignore_ascii_case("no")
                || trimmed.eq_ignore_ascii_case("off"))
        })
        .unwrap_or(true)
}

fn acquire_singleton_lock() -> Result<File> {
    let path =
        env::var("LESAVKA_UVC_LOCK_PATH").unwrap_or_else(|_| "/run/lesavka-uvc.lock".to_string());
    let file = OpenOptions::new()
        .read(true)
        .write(true)
        .create(true)
        .open(&path)
        .with_context(|| format!("open singleton lock {path}"))?;
    let rc = unsafe { libc::flock(file.as_raw_fd(), libc::LOCK_EX | libc::LOCK_NB) };
    if rc < 0 {
        let err = std::io::Error::last_os_error();
        match err.raw_os_error() {
            Some(code) if code == libc::EWOULDBLOCK || code == libc::EAGAIN => {
                eprintln!("[lesavka-uvc] another helper already owns {path}; exiting");
                std::process::exit(0);
            }
            _ => return Err(err).with_context(|| format!("lock singleton {path}")),
        }
    }
    Ok(file)
}

fn subscribe_event(fd: i32, req: libc::c_ulong, event: u32) -> Result<()> {
    let mut sub = V4l2EventSubscription {
        type_: event,
        id: 0,
        flags: 0,
        reserved: [0; 5],
    };
    let rc = unsafe { libc::ioctl(fd, req, &mut sub) };
    if rc < 0 {
        return Err(std::io::Error::last_os_error())
            .with_context(|| format!("subscribe event {event:#x} (fd={fd})"));
    }
    Ok(())
}

fn handle_setup(
    fd: i32,
    uvc_send_response: libc::c_ulong,
    state: &mut UvcState,
    pending: &mut Option<PendingRequest>,
    interfaces: UvcInterfaces,
    req: UsbCtrlRequest,
    debug: bool,
) {
    let selector = (req.w_value >> 8) as u8;
    let interface_lo = (req.w_index & 0xff) as u8;
    let interface_hi = (req.w_index >> 8) as u8;
    let interface_raw =
        if interface_hi == interfaces.streaming || interface_hi == interfaces.control {
            interface_hi
        } else if interface_lo == interfaces.streaming || interface_lo == interfaces.control {
            interface_lo
        } else {
            interface_hi
        };
    let is_in = (req.b_request_type & USB_DIR_IN) != 0;
    if matches!(selector, UVC_VS_PROBE_CONTROL | UVC_VS_COMMIT_CONTROL) {
        maybe_update_ctrl_len(state, req.w_length, debug);
    }
    let interface = map_interface(interface_raw, selector, interfaces, debug);

    if !is_in && req.b_request == UVC_SET_CUR {
        let len = req.w_length as usize;
        if interface == interfaces.control {
            // Accept SET_CUR on VC controls by replying with a zeroed payload.
            let payload = vec![0u8; len.min(UVC_DATA_SIZE)];
            let _ = send_response(fd, uvc_send_response, &payload);
            if debug {
                eprintln!(
                    "[lesavka-uvc] VC SET_CUR ack len={} iface={} sel={}",
                    req.w_length, interface, selector
                );
            }
            return;
        }
        if interface != interfaces.streaming {
            let _ = send_stall(fd, uvc_send_response);
            return;
        }
        if len > UVC_DATA_SIZE {
            eprintln!(
                "[lesavka-uvc] SET_CUR too large len={} (max={}); stalling",
                len, UVC_DATA_SIZE
            );
            let _ = send_stall(fd, uvc_send_response);
            return;
        }
        *pending = Some(PendingRequest {
            interface,
            selector,
            expected_len: len,
        });
        let payload = vec![0u8; len];
        let _ = send_response(fd, uvc_send_response, &payload);
        if debug {
            eprintln!(
                "[lesavka-uvc] SET_CUR queued len={} iface={} sel={}",
                req.w_length, interface, selector
            );
        }
        return;
    }

    if !is_in {
        let _ = send_stall(fd, uvc_send_response);
        return;
    }

    let payload = build_in_response(
        state,
        interfaces,
        interface,
        selector,
        req.b_request,
        req.w_length,
    );
    match payload {
        Some(bytes) => {
            if debug {
                eprintln!(
                    "[lesavka-uvc] send IN response rq=0x{:02x} sel={} len={}",
                    req.b_request,
                    selector,
                    bytes.len()
                );
            }
            let _ = send_response(fd, uvc_send_response, &bytes);
        }
        None => {
            let _ = send_stall(fd, uvc_send_response);
        }
    }
}

fn map_interface(raw: u8, selector: u8, interfaces: UvcInterfaces, debug: bool) -> u8 {
    let mapped = if selector == UVC_VS_PROBE_CONTROL {
        interfaces.streaming
    } else if selector == UVC_VS_COMMIT_CONTROL || selector == UVC_VC_REQUEST_ERROR_CODE_CONTROL {
        if raw == interfaces.control {
            interfaces.control
        } else {
            interfaces.streaming
        }
    } else {
        raw
    };

    if debug && mapped != raw {
        eprintln!("[lesavka-uvc] remapped interface {raw} -> {mapped} for selector {selector}");
    }

    mapped
}

fn maybe_update_ctrl_len(state: &mut UvcState, w_length: u16, debug: bool) {
    let want = w_length as usize;
    if !(want == STREAM_CTRL_SIZE_11 || want == STREAM_CTRL_SIZE_15) {
        return;
    }
    if state.ctrl_len == want {
        return;
    }

    state.ctrl_len = want;
    state.default = build_streaming_control(&state.cfg, state.ctrl_len);
    state.probe = state.default;
    state.commit = state.default;

    if debug {
        eprintln!("[lesavka-uvc] ctrl_len set to {}", state.ctrl_len);
    }
}

fn handle_data(
    _fd: i32,
    _uvc_send_response: libc::c_ulong,
    state: &mut UvcState,
    pending: &mut Option<PendingRequest>,
    interfaces: UvcInterfaces,
    data: UvcRequestData,
    debug: bool,
) {
    let Some(p) = pending.take() else {
        if debug {
            eprintln!("[lesavka-uvc] DATA with no pending request; ignoring");
        }
        return;
    };

    if data.length < 0 {
        return;
    }

    let len = data.length as usize;
    if debug && p.expected_len != 0 && len != p.expected_len {
        eprintln!(
            "[lesavka-uvc] DATA len mismatch: expected={} got={}",
            p.expected_len, len
        );
    }
    let slice = &data.data[..len.min(data.data.len())];
    if debug && slice.len() >= STREAM_CTRL_SIZE_11 {
        let interval = read_le32(slice, 4);
        let payload = read_le32(slice, 22);
        eprintln!(
            "[lesavka-uvc] data ctrl fmt={} frame={} interval={} payload={}",
            slice[2], slice[3], interval, payload
        );
    }

    if p.interface == interfaces.streaming
        && matches!(p.selector, UVC_VS_PROBE_CONTROL | UVC_VS_COMMIT_CONTROL)
    {
        let sanitized = sanitize_streaming_control(slice, state);
        if p.selector == UVC_VS_PROBE_CONTROL {
            state.probe = sanitized;
            if debug {
                let interval = read_le32(&state.probe, 4);
                let payload = read_le32(&state.probe, 22);
                eprintln!(
                    "[lesavka-uvc] probe set interval={} payload={}",
                    interval, payload
                );
                log_configfs_snapshot(state, "probe");
            }
        } else {
            state.commit = sanitized;
            if debug {
                let interval = read_le32(&state.commit, 4);
                let payload = read_le32(&state.commit, 22);
                eprintln!(
                    "[lesavka-uvc] commit set interval={} payload={}",
                    interval, payload
                );
                log_configfs_snapshot(state, "commit");
            }
        }
    }
}

fn build_in_response(
    state: &UvcState,
    interfaces: UvcInterfaces,
    interface: u8,
    selector: u8,
    request: u8,
    w_length: u16,
) -> Option<Vec<u8>> {
    let payload = match interface {
        _ if interface == interfaces.streaming => {
            build_streaming_response(state, selector, request)
        }
        _ if interface == interfaces.control => build_control_response(selector, request),
        _ => None,
    }?;

    Some(adjust_length(payload, w_length))
}

fn build_streaming_response(state: &UvcState, selector: u8, request: u8) -> Option<Vec<u8>> {
    let current = match selector {
        UVC_VS_PROBE_CONTROL => state.probe,
        UVC_VS_COMMIT_CONTROL => state.commit,
        _ => return None,
    };

    match request {
        UVC_GET_INFO => Some(vec![0x03]), // support GET/SET
        UVC_GET_LEN => Some((state.ctrl_len as u16).to_le_bytes().to_vec()),
        UVC_GET_CUR => Some(current[..state.ctrl_len].to_vec()),
        UVC_GET_MIN | UVC_GET_MAX | UVC_GET_DEF | UVC_GET_RES => {
            Some(state.default[..state.ctrl_len].to_vec())
        }
        _ => None,
    }
}

fn build_control_response(selector: u8, request: u8) -> Option<Vec<u8>> {
    match request {
        UVC_GET_INFO => Some(vec![0x03]), // indicate both GET/SET supported
        UVC_GET_LEN => Some(1u16.to_le_bytes().to_vec()),
        UVC_GET_CUR | UVC_GET_MIN | UVC_GET_MAX | UVC_GET_DEF | UVC_GET_RES => {
            if selector == UVC_VC_REQUEST_ERROR_CODE_CONTROL {
                // reset error code to “no error”
                Some(vec![0x00])
            } else {
                // simple 1‑byte placeholder for unhandled VC controls
                Some(vec![0x00])
            }
        }
        _ => None,
    }
}

fn sanitize_streaming_control(data: &[u8], state: &UvcState) -> [u8; STREAM_CTRL_SIZE_MAX] {
    let mut out = state.default;
    if data.len() >= STREAM_CTRL_SIZE_11 {
        let format_index = data[2];
        let frame_index = data[3];
        let interval = read_le32(data, 4);
        let host_payload = read_le32(data, 22);

        if format_index == 1 {
            out[2] = 1;
        }
        if frame_index == 1 {
            out[3] = 1;
        }
        if interval != 0 {
            write_le32(&mut out[4..8], interval);
        }
        if host_payload > 0 {
            let payload = host_payload.min(state.cfg.max_packet);
            write_le32(&mut out[22..26], payload);
        }
    }
    out
}

fn send_response(fd: i32, req: libc::c_ulong, payload: &[u8]) -> Result<()> {
    let mut resp = UvcRequestData {
        length: payload.len() as i32,
        data: [0u8; UVC_DATA_SIZE],
    };
    let n = payload.len().min(UVC_DATA_SIZE);
    resp.data[..n].copy_from_slice(&payload[..n]);

    let rc = unsafe { libc::ioctl(fd, req, &resp) };
    if rc < 0 {
        let err = std::io::Error::last_os_error();
        eprintln!("[lesavka-uvc] send_response failed: {err}");
        return Err(err).context("UVCIOC_SEND_RESPONSE");
    }
    Ok(())
}

fn send_stall(fd: i32, req: libc::c_ulong) -> Result<()> {
    let resp = UvcRequestData {
        length: -1,
        data: [0u8; UVC_DATA_SIZE],
    };
    let rc = unsafe { libc::ioctl(fd, req, &resp) };
    if rc < 0 {
        let err = std::io::Error::last_os_error();
        eprintln!("[lesavka-uvc] send_stall failed: {err}");
        return Err(err).context("UVCIOC_SEND_RESPONSE(stall)");
    }
    Ok(())
}

fn build_streaming_control(cfg: &UvcConfig, ctrl_len: usize) -> [u8; STREAM_CTRL_SIZE_MAX] {
    let mut buf = [0u8; STREAM_CTRL_SIZE_MAX];

    write_le16(&mut buf[0..2], 1); // bmHint: dwFrameInterval
    buf[2] = 1; // bFormatIndex
    buf[3] = 1; // bFrameIndex
    write_le32(&mut buf[4..8], cfg.interval);
    write_le16(&mut buf[8..10], 0);
    write_le16(&mut buf[10..12], 0);
    write_le16(&mut buf[12..14], 0);
    write_le16(&mut buf[14..16], 0);
    write_le16(&mut buf[16..18], 0);
    write_le32(&mut buf[18..22], cfg.frame_size);
    write_le32(&mut buf[22..26], cfg.max_packet);
    if ctrl_len >= STREAM_CTRL_SIZE_15 {
        write_le32(&mut buf[26..30], 48_000_000);
        buf[30] = 0x03; // bmFramingInfo: FID + EOF supported
        buf[31] = 0x01; // bPreferedVersion
        buf[32] = 0x01; // bMinVersion
        buf[33] = 0x01; // bMaxVersion
    }

    buf
}

fn event_bytes(ev: &V4l2Event) -> [u8; 64] {
    unsafe { ev.u.data }
}

fn parse_ctrl_request(data: [u8; 64]) -> UsbCtrlRequest {
    UsbCtrlRequest {
        b_request_type: data[0],
        b_request: data[1],
        w_value: u16::from_le_bytes([data[2], data[3]]),
        w_index: u16::from_le_bytes([data[4], data[5]]),
        w_length: u16::from_le_bytes([data[6], data[7]]),
    }
}

fn parse_request_data(data: [u8; 64]) -> UvcRequestData {
    let length = i32::from_le_bytes([data[0], data[1], data[2], data[3]]);
    let mut out = [0u8; UVC_DATA_SIZE];
    out.copy_from_slice(&data[4..64]);
    UvcRequestData { length, data: out }
}

fn stream_ctrl_len() -> usize {
    let value = env_u32("LESAVKA_UVC_CTRL_LEN", STREAM_CTRL_SIZE_15 as u32) as usize;
    match value {
        STREAM_CTRL_SIZE_11 | STREAM_CTRL_SIZE_15 => value,
        _ => STREAM_CTRL_SIZE_11,
    }
}

fn env_u32(name: &str, default: u32) -> u32 {
    env::var(name)
        .ok()
        .and_then(|v| v.parse::<u32>().ok())
        .unwrap_or(default)
}

fn env_u8(name: &str) -> Option<u8> {
    env::var(name).ok().and_then(|v| v.parse::<u8>().ok())
}

fn env_u32_opt(name: &str) -> Option<u32> {
    env::var(name).ok().and_then(|v| v.parse::<u32>().ok())
}

fn read_u32_file(path: &str) -> Option<u32> {
    std::fs::read_to_string(path)
        .ok()
        .and_then(|v| v.trim().parse::<u32>().ok())
}

fn read_u32_first(path: &str) -> Option<u32> {
    std::fs::read_to_string(path)
        .ok()
        .and_then(|v| v.split_whitespace().next()?.parse::<u32>().ok())
}

fn read_configfs_snapshot() -> Option<ConfigfsSnapshot> {
    let width = read_u32_file(&format!(
        "{CONFIGFS_UVC_BASE}/streaming/mjpeg/m/720p/wWidth"
    ))?;
    let height = read_u32_file(&format!(
        "{CONFIGFS_UVC_BASE}/streaming/mjpeg/m/720p/wHeight"
    ))?;
    let default_interval = read_u32_file(&format!(
        "{CONFIGFS_UVC_BASE}/streaming/mjpeg/m/720p/dwDefaultFrameInterval"
    ))?;
    let frame_interval = read_u32_first(&format!(
        "{CONFIGFS_UVC_BASE}/streaming/mjpeg/m/720p/dwFrameInterval"
    ))
    .unwrap_or(0);
    let maxpacket = read_u32_file(&format!("{CONFIGFS_UVC_BASE}/streaming_maxpacket"))?;
    let maxburst = read_u32_file(&format!("{CONFIGFS_UVC_BASE}/streaming_maxburst")).unwrap_or(0);
    Some(ConfigfsSnapshot {
        width,
        height,
        default_interval,
        frame_interval,
        maxpacket,
        maxburst,
    })
}

fn log_configfs_snapshot(state: &mut UvcState, label: &str) {
    let Some(current) = read_configfs_snapshot() else {
        eprintln!("[lesavka-uvc] configfs {label}: unavailable");
        return;
    };
    if state.cfg_snapshot == Some(current) {
        return;
    }
    eprintln!(
        "[lesavka-uvc] configfs {label}: {}x{} default_interval={} frame_interval={} maxpacket={} maxburst={}",
        current.width,
        current.height,
        current.default_interval,
        current.frame_interval,
        current.maxpacket,
        current.maxburst
    );
    state.cfg_snapshot = Some(current);
}

fn adjust_length(mut bytes: Vec<u8>, w_length: u16) -> Vec<u8> {
    let want = (w_length as usize).min(UVC_DATA_SIZE);
    if bytes.len() > want {
        bytes.truncate(want);
    } else if bytes.len() < want {
        bytes.resize(want, 0);
    }
    bytes
}

fn write_le16(dst: &mut [u8], val: u16) {
    let bytes = val.to_le_bytes();
    dst[0] = bytes[0];
    dst[1] = bytes[1];
}

fn write_le32(dst: &mut [u8], val: u32) {
    let bytes = val.to_le_bytes();
    dst[0] = bytes[0];
    dst[1] = bytes[1];
    dst[2] = bytes[2];
    dst[3] = bytes[3];
}

fn read_le32(src: &[u8], offset: usize) -> u32 {
    u32::from_le_bytes([
        src[offset],
        src[offset + 1],
        src[offset + 2],
        src[offset + 3],
    ])
}

fn compute_payload_cap(bulk: bool) -> Option<PayloadCap> {
    if let Some(limit) = env_u32_opt("LESAVKA_UVC_MAXPAYLOAD_LIMIT") {
        return Some(PayloadCap {
            limit,
            pct: 100,
            source: "env",
            periodic_dw: None,
            non_periodic_dw: None,
        });
    }

    let mut periodic =
        read_fifo_min("/sys/module/dwc2/parameters/g_tx_fifo_size").map(|v| (v, "dwc2.params"));
    let mut non_periodic =
        read_fifo_min("/sys/module/dwc2/parameters/g_np_tx_fifo_size").map(|v| (v, "dwc2.params"));
    if (periodic.is_none() || non_periodic.is_none())
        && let Some((p, np)) = read_debugfs_fifos()
    {
        if periodic.is_none() {
            periodic = p.map(|v| (v, "debugfs.params"));
        }
        if non_periodic.is_none() {
            non_periodic = np.map(|v| (v, "debugfs.params"));
        }
    }
    let periodic_dw = periodic.map(|(v, _)| v);
    let non_periodic_dw = non_periodic.map(|(v, _)| v);

    let (fifo_dw, source) = if bulk {
        if let Some((np, src)) = non_periodic {
            (np, src)
        } else if let Some((p, src)) = periodic {
            (p, src)
        } else {
            return None;
        }
    } else if let Some((p, src)) = periodic {
        (p, src)
    } else if let Some((np, src)) = non_periodic {
        (np, src)
    } else {
        return None;
    };

    let mut pct = env_u32("LESAVKA_UVC_LIMIT_PCT", 95);
    if pct == 0 {
        pct = 1;
    } else if pct > 100 {
        pct = 100;
    }
    let fifo_bytes = fifo_dw.saturating_mul(4);
    let limit = fifo_bytes.saturating_mul(pct) / 100;
    if limit == 0 {
        return None;
    }

    Some(PayloadCap {
        limit,
        pct,
        source,
        periodic_dw,
        non_periodic_dw,
    })
}

fn read_fifo_min(path: &str) -> Option<u32> {
    let raw = std::fs::read_to_string(path).ok()?;
    raw.split(|c: char| c == ',' || c.is_whitespace())
        .filter_map(|v| v.trim().parse::<u32>().ok())
        .filter(|v| *v > 0)
        .min()
}

fn read_debugfs_fifos() -> Option<(Option<u32>, Option<u32>)> {
    let udc = std::fs::read_dir("/sys/class/udc")
        .ok()?
        .filter_map(|e| e.ok())
        .filter_map(|e| e.file_name().into_string().ok())
        .next()?;
    let path = format!("/sys/kernel/debug/usb/{udc}/params");
    let text = std::fs::read_to_string(path).ok()?;
    let mut periodic: Option<u32> = None;
    let mut non_periodic: Option<u32> = None;
    for line in text.lines() {
        let mut parts = line.splitn(2, ':');
        let key = match parts.next() {
            Some(v) => v.trim(),
            None => continue,
        };
        let val = match parts.next().and_then(|v| v.trim().parse::<u32>().ok()) {
            Some(v) => v,
            None => continue,
        };
        if key == "g_np_tx_fifo_size" {
            non_periodic = Some(val);
        } else if key.starts_with("g_tx_fifo_size[") && val > 0 {
            periodic = Some(match periodic {
                Some(prev) => prev.min(val),
                None => val,
            });
        }
    }
    if periodic.is_none() && non_periodic.is_none() {
        None
    } else {
        Some((periodic, non_periodic))
    }
}

const IOC_NRBITS: u8 = 8;
const IOC_TYPEBITS: u8 = 8;
const IOC_SIZEBITS: u8 = 14;
const IOC_NRSHIFT: u8 = 0;
const IOC_TYPESHIFT: u8 = IOC_NRSHIFT + IOC_NRBITS;
const IOC_SIZESHIFT: u8 = IOC_TYPESHIFT + IOC_TYPEBITS;
const IOC_DIRSHIFT: u8 = IOC_SIZESHIFT + IOC_SIZEBITS;
const IOC_READ: u8 = 2;
const IOC_WRITE: u8 = 1;

fn ioctl_read<T>(type_: u8, nr: u8) -> libc::c_ulong {
    ioc(IOC_READ, type_, nr, std::mem::size_of::<T>() as u16)
}

fn ioctl_write<T>(type_: u8, nr: u8) -> libc::c_ulong {
    ioc(IOC_WRITE, type_, nr, std::mem::size_of::<T>() as u16)
}

fn ioc(dir: u8, type_: u8, nr: u8, size: u16) -> libc::c_ulong {
    let dir = (dir as u32) << IOC_DIRSHIFT;
    let ty = (type_ as u32) << IOC_TYPESHIFT;
    let nr = (nr as u32) << IOC_NRSHIFT;
    let size = (size as u32) << IOC_SIZESHIFT;
    (dir | ty | nr | size) as libc::c_ulong
}