uvc: clamp to configfs maxpacket

server/src/bin/lesavka-uvc.rs

@@ -301,6 +301,22 @@ impl UvcConfig {
                 max_packet
             );
         }
+        if let Some(cfg_max) = read_u32_file(
+            "/sys/kernel/config/usb_gadget/lesavka/functions/uvc.usb0/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 {
@@ -773,6 +789,12 @@ 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 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 {