From 803eb463a54c54bb623176573c51f382f52ee9a9 Mon Sep 17 00:00:00 2001
From: Laurent Bercot <ska-skaware@skarnet.org>
Date: Sun, 25 Jun 2023 18:16:43 +0000
Subject:  Loosen nonzero servicedirs requirement on s6-svwait/s6-svlisten

Signed-off-by: Laurent Bercot <ska@appnovation.com>
---
 doc/s6-svlisten.html          | 2 ++
 doc/s6-svwait.html            | 2 +-
 src/supervision/s6-svlisten.c | 4 +++-
 src/supervision/s6-svwait.c   | 2 +-
 4 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/doc/s6-svlisten.html b/doc/s6-svlisten.html
index 8fdbc88..96d3f74 100644
--- a/doc/s6-svlisten.html
+++ b/doc/s6-svlisten.html
@@ -52,6 +52,8 @@ their state changes. </li>
  <li> It spawns <em>prog...</em> as a child right after getting the
 initial state of all the monitored services. </li>
  <li> It then blocks until the wanted state happens. </li>
+ <li> If no service directories are listed (the block is empty), then
+instead of doing all that, it immediately execs into <em>prog...</em>.
 </ul>
 
 <h2> Exit codes </h2>
diff --git a/doc/s6-svwait.html b/doc/s6-svwait.html
index 553201b..daa497f 100644
--- a/doc/s6-svwait.html
+++ b/doc/s6-svwait.html
@@ -35,7 +35,7 @@ s6-svwait only waits for notifications; it never polls.
 <p>
 s6-svwait monitors one or more <a href="servicedir.html">service
 directories</a> given as its arguments, waiting for a state (ready, up or down) to
-happen.
+happen. If no service directories are listed, it immediately exits 0.
 </p>
 
 <h2> Exit codes </h2>
diff --git a/src/supervision/s6-svlisten.c b/src/supervision/s6-svlisten.c
index 205a382..2ab1d9b 100644
--- a/src/supervision/s6-svlisten.c
+++ b/src/supervision/s6-svlisten.c
@@ -9,6 +9,7 @@
 #include <skalibs/strerr.h>
 #include <skalibs/djbunix.h>
 #include <skalibs/selfpipe.h>
+#include <skalibs/exec.h>
 
 #include <s6/compat.h>
 #include "s6-svlisten.h"
@@ -49,8 +50,9 @@ int main (int argc, char const **argv, char const *const *envp)
   }
   if (argc < 3) dieusage() ;
   argc1 = s6_el_semicolon(argv) ;
-  if (!argc1 || argc == argc1 + 1) dieusage() ;
+  if (argc == argc1 + 1) dieusage() ;
   if (argc1 >= argc) strerr_dief1x(100, "unterminated servicedir block") ;
+  if (!argc1) xexec(argv + argc1 + 1) ;
   if (wantup == 2 && or)
   {
     or = 0 ;
diff --git a/src/supervision/s6-svwait.c b/src/supervision/s6-svwait.c
index 2c7a312..78f5c3f 100644
--- a/src/supervision/s6-svwait.c
+++ b/src/supervision/s6-svwait.c
@@ -45,7 +45,7 @@ int main (int argc, char const *const *argv)
     argc -= l.ind ; argv += l.ind ;
     if (t) tain_from_millisecs(&deadline, t) ; else deadline = tain_infinite_relative ;
   }
-  if (!argc) dieusage() ;
+  if (!argc) return 0 ;
   tain_now_set_stopwatch_g() ;
   tain_add_g(&deadline, &deadline) ;
 
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