trace: add trace_event_get_state_backends()

Code that checks dstate is unaware of SystemTap and LTTng UST dstate, so
the following trace event will not fire when solely enabled by SystemTap
or LTTng UST:

  if (trace_event_get_state(TRACE_MY_EVENT)) {
      str = g_strdup_printf("Expensive string to generate ...",
                            ...);
      trace_my_event(str);
      g_free(str);
  }

Add trace_event_get_state_backends() to fetch backend dstate.  Those
backends that use QEMU dstate fetch it as part of
generate_h_backend_dstate().

Update existing trace_event_get_state() callers to use
trace_event_get_state_backends() instead.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170731140718.22010-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 5 insertions, 8 deletions

diff --git a/hw/usb/hcd-ohci.c b/hw/usb/hcd-ohci.c
index 3ada35e..267982e 100644
--- a/hw/usb/hcd-ohci.c
+++ b/hw/usb/hcd-ohci.c
@@ -936,16 +936,18 @@ static int ohci_service_iso_td(OHCIState *ohci, struct ohci_ed *ed,
     return 1;
 }
 
-#ifdef trace_event_get_state
 static void ohci_td_pkt(const char *msg, const uint8_t *buf, size_t len)
 {
-    bool print16 = !!trace_event_get_state(TRACE_USB_OHCI_TD_PKT_SHORT);
-    bool printall = !!trace_event_get_state(TRACE_USB_OHCI_TD_PKT_FULL);
+    bool print16;
+    bool printall;
     const int width = 16;
     int i;
     char tmp[3 * width + 1];
     char *p = tmp;
 
+    print16 = !!trace_event_get_state_backends(TRACE_USB_OHCI_TD_PKT_SHORT);
+    printall = !!trace_event_get_state_backends(TRACE_USB_OHCI_TD_PKT_FULL);
+
     if (!printall && !print16) {
         return;
     }
@@ -967,11 +969,6 @@ static void ohci_td_pkt(const char *msg, const uint8_t *buf, size_t len)
         p += sprintf(p, " %.2x", buf[i]);
     }
 }
-#else
-static void ohci_td_pkt(const char *msg, const uint8_t *buf, size_t len)
-{
-}
-#endif
 
 /* Service a transport descriptor.
    Returns nonzero to terminate processing of this endpoint.  */