commit fd034a7aaa0f76cbaf65c8933f05e53f0e6e4f2c
Author: Fletcher Woodruff <fletcherw@chromium.org>
Date:   Tue Jun 16 13:59:10 2020 -0600

    Log errno when acquiring usb connection fails

diff --git a/src/usb.c b/src/usb.c
index aa05960..905b90b 100644
--- a/src/usb.c
+++ b/src/usb.c
@@ -19,6 +19,7 @@
 #include <time.h>
 #include <string.h>
 #include <unistd.h>
+#include <errno.h>
 
 #include <libusb.h>
 
@@ -686,9 +687,17 @@ struct usb_conn_t *usb_conn_acquire(struct usb_sock_t *usb)
 
     /* Sanity check: Is the interface still free */
     if (sem_trywait(&uf->lock)) {
-      ERR("Interface #%d (%d) already in use!",
-	  conn->interface_index,
-	  uf->libusb_interface_index);
+      int error = errno;
+      if (error == EAGAIN) {
+	ERR("Interface #%d (%d) already in use!",
+	    conn->interface_index,
+	    uf->libusb_interface_index);
+      } else {
+	ERR("sem_trywait on interface #%d (%d) failed with error %d",
+	    conn->interface_index,
+	    uf->libusb_interface_index,
+	    error);
+      }
       goto acquire_error;
     }