From 6c13d05eae563fcee73a761996329f27e153c02c Mon Sep 17 00:00:00 2001
From: Luca Toniolo <10792599+grandixximo@users.noreply.github.com>
Date: Fri, 7 Aug 2026 22:46:45 +1000
Subject: [PATCH] halscope: fix "loadrt scope_rt failed" when reopening the
 scope

Closing halscope leaves scope_rt loaded, so every launch after the first
has to detect that the realtime part is already there and skip the
loadrt. That detection broke in d88d10db8f: the funct lookup
halpr_find_funct_by_name("scope.sample") was replaced with the component
lookup hal_comp_by_name("scope.sample", NULL). No component is named
"scope.sample" (the component is "scope_rt", "scope.sample" is the funct
it exports), so the lookup always returns -ENOENT and halscope always
runs "halcmd loadrt scope_rt".

On the second launch that loadrt fails because scope_rt is already
loaded, and halscope exits immediately with "loadrt scope_rt failed".
From a GUI such as AXIS ("Machine" > "Hal Scope") the window simply
never appears again until LinuxCNC is restarted.

Look the funct up with hal_list_funct() instead, the same way
scope_horiz.c already does, which restores the original semantics.
---
 src/hal/utils/scope.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/hal/utils/scope.c b/src/hal/utils/scope.c
index 45327d5ced4..dd96030ee29 100644
--- a/src/hal/utils/scope.c
+++ b/src/hal/utils/scope.c
@@ -99,6 +99,15 @@ static void exit_on_signal(int signum) {
     exit(1);
 }
 
+/* callback for hal_list_funct(), matches a function by name */
+static int find_funct_cb(hal_query_t *q, void *arg)
+{
+    if (!strcmp((const char *)arg, q->name)) {
+        return 1;  /* positive, break the loop without error */
+    }
+    return 0;
+}
+
 /* Read just the SAMPLES value from config file before loading scope_rt */
 static int read_samples_from_config(const char *filename)
 {
@@ -199,8 +208,9 @@ int main(int argc, gchar * argv[])
 	return -1;
     }
 
-    int rv = hal_comp_by_name("scope.sample", NULL);
-    if (-ENOENT == rv) {
+    hal_query_t qf = {};
+    int rv = hal_list_funct(&qf, find_funct_cb, (void *)"scope.sample");
+    if (0 == rv) {
 	char buf[1000];
 	snprintf(buf, sizeof(buf), EMC2_BIN_DIR "/halcmd loadrt scope_rt num_samples=%d",
 		num_samples);
@@ -209,12 +219,15 @@ int main(int argc, gchar * argv[])
 	    hal_exit(comp_id);
 	    exit(1);
 	}
-    } else {
+    } else if (rv > 0) {
 	/* scope_rt already loaded - we'll check if sample count matches later */
-        if(0 == rv)
-            rtapi_print_msg(RTAPI_MSG_DBG, "SCOPE: scope_rt already loaded, requested %d samples\n", num_samples);
-        else
-            rtapi_print_msg(RTAPI_MSG_DBG, "SCOPE: hal_comp_by_name() returned error %d\n", rv);
+        rtapi_print_msg(RTAPI_MSG_DBG, "SCOPE: scope_rt already loaded, requested %d samples\n", num_samples);
+    } else {
+	/* the query itself failed, we cannot tell whether scope_rt is loaded
+	   and must not try to load it again */
+        rtapi_print_msg(RTAPI_MSG_ERR, "SCOPE: ERROR: hal_list_funct() returned error %d (%s)\n", rv, hal_strerror(rv));
+        hal_exit(comp_id);
+        exit(1);
     }
     /* set up a shared memory region for the scope data */
     shm_id = rtapi_shmem_new(SCOPE_SHM_KEY, comp_id, sizeof(scope_shm_control_t));