From 6f9dc69704211a6123b225036bffb46c1a2d6e83 Mon Sep 17 00:00:00 2001
From: Laurent Bercot <ska-skaware@skarnet.org>
Date: Thu, 31 Jan 2019 20:33:42 +0000
Subject:  Make "s6-svc -wu foo" wait for foo to be up. Document supervise/
 creation.

---
 doc/s6-supervise.html    |  2 ++
 src/libs6/s6_svc_write.c | 29 ++++++++++++++++-------------
 src/supervision/s6-svc.c | 14 ++++++++------
 3 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/doc/s6-supervise.html b/doc/s6-supervise.html
index f5cb269..2926f83 100644
--- a/doc/s6-supervise.html
+++ b/doc/s6-supervise.html
@@ -122,6 +122,8 @@ the service stops, as if a
 <ul>
  <li> s6-supervise switches to the <em>servicedir</em>
 <a href="servicedir.html">service directory</a>. </li>
+ <li> It creates a <tt>supervise/</tt> subdirectory (if it doesn't exist yet) to
+store its internal data. </li>
  <li> It exits 100 if another s6-supervise process is already monitoring this service. </li>
  <li> If the <tt>./event</tt> <a href="fifodir.html">fifodir</a> does not exist,
 s6-supervise creates it and allows subscriptions to it from processes having the same
diff --git a/src/libs6/s6_svc_write.c b/src/libs6/s6_svc_write.c
index 70c3964..46d3178 100644
--- a/src/libs6/s6_svc_write.c
+++ b/src/libs6/s6_svc_write.c
@@ -7,21 +7,24 @@
 
 int s6_svc_write (char const *fifo, char const *data, size_t datalen)
 {
-  int fd = open_write(fifo) ;
-  if (fd < 0) switch (errno)
-  {
-    case ENXIO : return 0 ;
-    case ENOENT :
-    case ENOTDIR :
-    case EISDIR : return -2 ;
-    default : return -1 ;
-  }
-  if (ndelay_off(fd) == -1) return -1 ;
-  if (fd_write(fd, data, datalen) == -1)
+  if (datalen)
   {
+    int fd = open_write(fifo) ;
+    if (fd < 0) switch (errno)
+    {
+      case ENXIO : return 0 ;
+      case ENOENT :
+      case ENOTDIR :
+      case EISDIR : return -2 ;
+      default : return -1 ;
+    }
+    if (ndelay_off(fd) == -1) return -1 ;
+    if (fd_write(fd, data, datalen) == -1)
+    {
+      fd_close(fd) ;
+      return -1 ;
+    }
     fd_close(fd) ;
-    return -1 ;
   }
-  fd_close(fd) ;
   return 1 ;
 }
diff --git a/src/supervision/s6-svc.c b/src/supervision/s6-svc.c
index ee7ddc5..6a5d64b 100644
--- a/src/supervision/s6-svc.c
+++ b/src/supervision/s6-svc.c
@@ -69,7 +69,6 @@ int main (int argc, char const *const *argv, char const *const *envp)
   if (!argc) dieusage() ;
   if (argc > 1) strerr_warn1x("ignoring extra arguments") ;
 
-  if (datalen <= 1) return 0 ;
   if (updown[1] == 'U' || updown[1] == 'R')
   {
     size_t arglen = strlen(argv[0]) ;
@@ -89,7 +88,7 @@ int main (int argc, char const *const *argv, char const *const *envp)
     char const *newargv[11] ;
     unsigned int m = 0 ;
     char fmt[UINT_FMT] ;
-    newargv[m++] = S6_BINPREFIX "s6-svlisten1" ;
+    newargv[m++] = datalen > 1 ? S6_BINPREFIX "s6-svlisten1" : S6_BINPREFIX "s6-svwait" ;
     newargv[m++] = updown ;
     if (timeout)
     {
@@ -99,10 +98,13 @@ int main (int argc, char const *const *argv, char const *const *envp)
     }
     newargv[m++] = "--" ;
     newargv[m++] = argv[0] ;
-    newargv[m++] = S6_BINPREFIX "s6-svc" ;
-    newargv[m++] = data ;
-    newargv[m++] = "--" ;
-    newargv[m++] = argv[0] ;
+    if (datalen > 1)
+    {
+      newargv[m++] = S6_BINPREFIX "s6-svc" ;
+      newargv[m++] = data ;
+      newargv[m++] = "--" ;
+      newargv[m++] = argv[0] ;
+    }
     newargv[m++] = 0 ;
     xpathexec_run(newargv[0], newargv, envp) ;
   }
-- 
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