From 8274d2d3fc798932210017fa89fb77f690900074 Mon Sep 17 00:00:00 2001
From: Luca Toniolo <10792599+grandixximo@users.noreply.github.com>
Date: Tue, 2 Jun 2026 21:19:51 +0800
Subject: [PATCH 1/3] latency-test, latency-histogram: warn when rtapi_app
 lacks RT privileges

Without 'sudo make setuid' (or 'sudo make setcap') rtapi_app runs
unprivileged: no SCHED_FIFO, no locked memory, so latency readings are
wildly inflated and easy to mistake for a code regression. Warn, for a
non-root user, when rtapi_app is neither setuid root nor carries the
cap_sys_nice capability.

Closes #4044
---
 scripts/latency-histogram | 21 +++++++++++++++++++++
 scripts/latency-test      | 21 +++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/scripts/latency-histogram b/scripts/latency-histogram
index 014b63f582f..cf9fc662b27 100755
--- a/scripts/latency-histogram
+++ b/scripts/latency-histogram
@@ -111,6 +111,26 @@ proc which_exe {name} {
   return -code error "$name: executable not found"
 } ;# which_exe
 
+proc check_rt_privileges {} {
+  # Without 'sudo make setuid' (or 'sudo make setcap') rtapi_app runs
+  # unprivileged: realtime threads get no SCHED_FIFO and no locked memory, so
+  # the latency readings are wildly inflated.  Warn rather than mislead.
+  if {![catch {exec id -u} uid] && $uid == 0} return ;# root has every privilege
+  if {[catch {which_exe rtapi_app} rtapi]} return ;# cannot locate, stay quiet
+  if {![catch {file attributes $rtapi -permissions} mode] && ($mode & 04000)} return ;# setuid root
+  if {![catch {exec getcap $rtapi} caps] && [string match *cap_sys_nice* $caps]} return ;# file caps
+  set msg "Warning: rtapi_app is not setuid root and has no realtime capabilities."
+  append msg "\nRealtime threads get no SCHED_FIFO priority or locked memory,"
+  append msg "\nso the latency shown will be far worse than reality."
+  append msg "\nRun 'sudo make setuid' (or 'sudo make setcap') in src/."
+  puts stderr $msg
+  if {$::LH(use_x)} {
+    package require Tk
+    tk_messageBox -parent . -icon warning -type ok \
+        -title "Latency Warning" -message $msg
+  }
+} ;# check_rt_privileges
+
 proc program_check {plist} {
   foreach prog $plist {
     if [catch {
@@ -944,6 +964,7 @@ proc windowToFile { win } {
 if ![info exists ::LH(start)] {
   set_defaults
   config
+  check_rt_privileges
   progress "Loading packages"
   load_packages
   signal trap SIGINT finish
diff --git a/scripts/latency-test b/scripts/latency-test
index 63b34c0034d..334cee44e07 100755
--- a/scripts/latency-test
+++ b/scripts/latency-test
@@ -16,6 +16,25 @@ kversion=$(uname -v)
 calc() { awk "BEGIN { print ($1); }" < /dev/null; }
 icalc() { awk "BEGIN { printf \"%.0f\n\", ($1); }" < /dev/null; }
 
+# Without 'sudo make setuid' (or 'sudo make setcap') rtapi_app runs
+# unprivileged: realtime threads get no SCHED_FIFO and no locked memory, so the
+# latency readings are wildly inflated.  Warn rather than mislead.
+check_rt_privileges () {
+    [ "$(id -u)" = 0 ] && return 0          # root has every privilege
+    rtapi_app=$(command -v rtapi_app) || return 0
+    [ -n "$rtapi_app" ] || return 0
+    [ -u "$rtapi_app" ] && return 0         # setuid root
+    if command -v getcap >/dev/null 2>&1; then
+        case $(getcap "$rtapi_app" 2>/dev/null) in
+            *cap_sys_nice*) return 0 ;;     # file capabilities
+        esac
+    fi
+    echo "Warning: rtapi_app is not setuid root and has no realtime capabilities." >&2
+    echo "         Realtime threads get no SCHED_FIFO priority or locked memory," >&2
+    echo "         so the latency shown will be far worse than reality." >&2
+    echo "         Run 'sudo make setuid' (or 'sudo make setcap') in src/." >&2
+}
+
 parse_time () {
     case $1 in
     -)   echo "0" ;;
@@ -170,4 +189,6 @@ L=\$(($SIGNALS
 echo \$L > "$HOME"/.latency
 EOF
 
+check_rt_privileges
+
 halrun lat.hal

From ecc6b299dabf83b1a7fe0fbd8d7e3f208683204c Mon Sep 17 00:00:00 2001
From: Luca Toniolo <10792599+grandixximo@users.noreply.github.com>
Date: Tue, 2 Jun 2026 22:25:37 +0800
Subject: [PATCH 2/3] latency: skip RT-privilege warning on non-RT kernels

Only warn under PREEMPT_RT or RTAI; on a non-RT kernel the privileges
do not matter, so the check would be noise.
---
 scripts/latency-histogram | 5 +++++
 scripts/latency-test      | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/scripts/latency-histogram b/scripts/latency-histogram
index cf9fc662b27..160da08ba4f 100755
--- a/scripts/latency-histogram
+++ b/scripts/latency-histogram
@@ -115,6 +115,11 @@ proc check_rt_privileges {} {
   # Without 'sudo make setuid' (or 'sudo make setcap') rtapi_app runs
   # unprivileged: realtime threads get no SCHED_FIFO and no locked memory, so
   # the latency readings are wildly inflated.  Warn rather than mislead.
+  # Only meaningful on an RT-capable kernel; stay quiet on non-RT (e.g. dev).
+  set rt 0
+  if {![catch {exec uname -v} kv] && [string match *PREEMPT_RT* $kv]} {set rt 1}
+  if {[string first rtai [string tolower $::tcl_platform(osVersion)]] >= 0} {set rt 1}
+  if {!$rt} return
   if {![catch {exec id -u} uid] && $uid == 0} return ;# root has every privilege
   if {[catch {which_exe rtapi_app} rtapi]} return ;# cannot locate, stay quiet
   if {![catch {file attributes $rtapi -permissions} mode] && ($mode & 04000)} return ;# setuid root
diff --git a/scripts/latency-test b/scripts/latency-test
index 334cee44e07..94bab7e1dcf 100755
--- a/scripts/latency-test
+++ b/scripts/latency-test
@@ -20,6 +20,11 @@ icalc() { awk "BEGIN { printf \"%.0f\n\", ($1); }" < /dev/null; }
 # unprivileged: realtime threads get no SCHED_FIFO and no locked memory, so the
 # latency readings are wildly inflated.  Warn rather than mislead.
 check_rt_privileges () {
+    # only meaningful on an RT-capable kernel; stay quiet on non-RT (e.g. dev)
+    case "$(uname -v) $(uname -r)" in
+        *PREEMPT_RT*|*rtai*) ;;
+        *) return 0 ;;
+    esac
     [ "$(id -u)" = 0 ] && return 0          # root has every privilege
     rtapi_app=$(command -v rtapi_app) || return 0
     [ -n "$rtapi_app" ] || return 0

From a3df81c6c06486f17790f36817f1c52f7bb31957 Mon Sep 17 00:00:00 2001
From: Luca Toniolo <10792599+grandixximo@users.noreply.github.com>
Date: Fri, 5 Jun 2026 08:38:15 +0800
Subject: [PATCH 3/3] latency: detect realtime via halcmd getrt instead of
 setuid heuristic

Query realtime status with 'halcmd getrt' (hdiethelm's PR) rather than
probing the setuid bit. latency-histogram asks inside its own running
session, so no stray HAL segment is created. latency-test drops its
check and relies on the existing "POSIX non-realtime" note.
---
 scripts/latency-histogram | 25 +++++++++----------------
 scripts/latency-test      | 26 --------------------------
 2 files changed, 9 insertions(+), 42 deletions(-)

diff --git a/scripts/latency-histogram b/scripts/latency-histogram
index 160da08ba4f..4ccd70a820e 100755
--- a/scripts/latency-histogram
+++ b/scripts/latency-histogram
@@ -112,22 +112,15 @@ proc which_exe {name} {
 } ;# which_exe
 
 proc check_rt_privileges {} {
-  # Without 'sudo make setuid' (or 'sudo make setcap') rtapi_app runs
-  # unprivileged: realtime threads get no SCHED_FIFO and no locked memory, so
-  # the latency readings are wildly inflated.  Warn rather than mislead.
-  # Only meaningful on an RT-capable kernel; stay quiet on non-RT (e.g. dev).
-  set rt 0
-  if {![catch {exec uname -v} kv] && [string match *PREEMPT_RT* $kv]} {set rt 1}
-  if {[string first rtai [string tolower $::tcl_platform(osVersion)]] >= 0} {set rt 1}
-  if {!$rt} return
-  if {![catch {exec id -u} uid] && $uid == 0} return ;# root has every privilege
-  if {[catch {which_exe rtapi_app} rtapi]} return ;# cannot locate, stay quiet
-  if {![catch {file attributes $rtapi -permissions} mode] && ($mode & 04000)} return ;# setuid root
-  if {![catch {exec getcap $rtapi} caps] && [string match *cap_sys_nice* $caps]} return ;# file caps
-  set msg "Warning: rtapi_app is not setuid root and has no realtime capabilities."
-  append msg "\nRealtime threads get no SCHED_FIFO priority or locked memory,"
+  # Query the running session (realtime already up) via 'halcmd getrt'.
+  # Warn on "No realtime available", usually a missing 'sudo make setuid'.
+  set out ""
+  catch {exec $::LH(prog,halcmd) getrt 2>@1} out
+  if {![string match {*No realtime available*} $out]} return
+  set msg "Warning: realtime is not available."
+  append msg "\nThreads get no SCHED_FIFO priority or locked memory,"
   append msg "\nso the latency shown will be far worse than reality."
-  append msg "\nRun 'sudo make setuid' (or 'sudo make setcap') in src/."
+  append msg "\nOn a run-in-place build, run 'sudo make setuid' (or 'sudo make setcap') in src/."
   puts stderr $msg
   if {$::LH(use_x)} {
     package require Tk
@@ -647,6 +640,7 @@ proc start_collection {} {
     }
   }
   hal start
+  check_rt_privileges
   if {!$::LH(legacy)} {
     # Attach the Tcl hal_stream binding (added in halsh.c) to each
     # thread's latencybinstream FIFO. The handle stays open for the
@@ -969,7 +963,6 @@ proc windowToFile { win } {
 if ![info exists ::LH(start)] {
   set_defaults
   config
-  check_rt_privileges
   progress "Loading packages"
   load_packages
   signal trap SIGINT finish
diff --git a/scripts/latency-test b/scripts/latency-test
index 94bab7e1dcf..63b34c0034d 100755
--- a/scripts/latency-test
+++ b/scripts/latency-test
@@ -16,30 +16,6 @@ kversion=$(uname -v)
 calc() { awk "BEGIN { print ($1); }" < /dev/null; }
 icalc() { awk "BEGIN { printf \"%.0f\n\", ($1); }" < /dev/null; }
 
-# Without 'sudo make setuid' (or 'sudo make setcap') rtapi_app runs
-# unprivileged: realtime threads get no SCHED_FIFO and no locked memory, so the
-# latency readings are wildly inflated.  Warn rather than mislead.
-check_rt_privileges () {
-    # only meaningful on an RT-capable kernel; stay quiet on non-RT (e.g. dev)
-    case "$(uname -v) $(uname -r)" in
-        *PREEMPT_RT*|*rtai*) ;;
-        *) return 0 ;;
-    esac
-    [ "$(id -u)" = 0 ] && return 0          # root has every privilege
-    rtapi_app=$(command -v rtapi_app) || return 0
-    [ -n "$rtapi_app" ] || return 0
-    [ -u "$rtapi_app" ] && return 0         # setuid root
-    if command -v getcap >/dev/null 2>&1; then
-        case $(getcap "$rtapi_app" 2>/dev/null) in
-            *cap_sys_nice*) return 0 ;;     # file capabilities
-        esac
-    fi
-    echo "Warning: rtapi_app is not setuid root and has no realtime capabilities." >&2
-    echo "         Realtime threads get no SCHED_FIFO priority or locked memory," >&2
-    echo "         so the latency shown will be far worse than reality." >&2
-    echo "         Run 'sudo make setuid' (or 'sudo make setcap') in src/." >&2
-}
-
 parse_time () {
     case $1 in
     -)   echo "0" ;;
@@ -194,6 +170,4 @@ L=\$(($SIGNALS
 echo \$L > "$HOME"/.latency
 EOF
 
-check_rt_privileges
-
 halrun lat.hal