Fix and improve report_sched_fifo_error()

Author: hdiethelm

src/rtapi/uspace_rtapi_main.cc

@@ -105,14 +105,14 @@ static inline int detect_preempt_dynamic() {
 }
 
 #ifdef USPACE_RTAI
-static int detect_rtai() {
+static int detect_rtai_lxrt() {
     if(!has_setuid_root()) return 0;
     struct utsname u;
     uname(&u);
     return strcasestr (u.release, "-rtai") != 0;
 }
 #else
-static int detect_rtai() {
+static int detect_rtai_lxrt() {
     return 0;
 }
 #endif
@@ -166,13 +166,17 @@ static void report_sched_fifo_error(int sched_err){
     // between "no caps", "stock kernel", or "wrong rlimits" (issue
     // #3928).  errno comes from the SCHED_FIFO probe in
     // can_set_sched_fifo(); cap state comes from libcap.
-#ifdef __linux__
-    cap_t caps = cap_get_proc();
-    const char *nice_s = cap_effective_str(caps, CAP_SYS_NICE);
-    const char *lock_s = cap_effective_str(caps, CAP_IPC_LOCK);
-#else
     const char *nice_s = "unknown";
     const char *lock_s = "unknown";
+#ifdef __linux__
+    cap_t caps = cap_get_proc();
+    if(caps == NULL){
+        rtapi_print_msg(RTAPI_MSG_ERR, "cap_get_proc failed: %m\n");
+    }else{
+        nice_s = cap_effective_str(caps, CAP_SYS_NICE);
+        lock_s = cap_effective_str(caps, CAP_IPC_LOCK);
+        cap_free(caps);
+    }
 #endif
     rtapi_print_msg(RTAPI_MSG_ERR,
         "Note: realtime scheduling unavailable "
@@ -184,9 +188,6 @@ static void report_sched_fifo_error(int sched_err){
         "  Override (testing only): set LINUXCNC_FORCE_REALTIME=1.\n",
         sched_err ? strerror(sched_err) : "denied",
         nice_s, lock_s);
-#ifdef __linux__
-    if (caps) cap_free(caps);
-#endif
 }
 
 // Success-probe for realtime scheduling: briefly try to set SCHED_FIFO on
@@ -231,7 +232,7 @@ rtapi_realtime_status_t rtapi_realtime_status(void){
         return cached;
     }
 
-    if(detect_rtai()){
+    if(detect_rtai_lxrt()){
         cached = REALTIME_STATUS_LXRT;
         return cached;
     }