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.

Author: grandixximo

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

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