Make "s6-svc -wu foo" wait for foo to be up. Document supervise/ creation.

1 files changed, 16 insertions, 13 deletions

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 ;
 }