Add console holder functionality to s6-svscan

5 files changed, 28 insertions, 5 deletions

diff --git a/COPYING b/COPYING
index f019bc7..b956149 100644
--- a/COPYING
+++ b/COPYING
@@ -1,4 +1,4 @@
-Copyright (c) 2011-2019 Laurent Bercot <ska-skaware@skarnet.org>
+Copyright (c) 2011-2020 Laurent Bercot <ska-skaware@skarnet.org>
 
 Permission to use, copy, modify, and distribute this software for any
 purpose with or without fee is hereby granted, provided that the above
diff --git a/NEWS b/NEWS
index 10e4176..cedcd29 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,7 @@ In 2.9.1.0
  - execline support is now optional. Some functionality is not available
 when execline support is disabled.
  - New '?' directive to s6-log, to spawn a processor with /bin/sh.
+ - New console holder functionality for easier s6-svscan-log support.
 
 
 In 2.9.0.1
diff --git a/doc/s6-svscan.html b/doc/s6-svscan.html
index 665fd75..b826847 100644
--- a/doc/s6-svscan.html
+++ b/doc/s6-svscan.html
@@ -27,7 +27,7 @@ the root or a branch of a <em>supervision tree</em>.
 <h2> Interface </h2>
 
 <pre>
-     s6-svscan [ -S | -s ] [ -d <em>notif</em> ] [ -c max ] [ -t <em>rescan</em> ] [ <em>scandir</em> ]
+     s6-svscan [ -S | -s ] [ -d <em>notif</em> ] [ -X <em>consoleholder</em> ] [ -c max ] [ -t <em>rescan</em> ] [ <em>scandir</em> ]
 </pre>
 
 <ul>
@@ -73,6 +73,14 @@ even that the relevant <a href="s6-supervise.html">s6-supervise</a> processes ha
 been started. If you need to test for <em>deep readiness</em>, meaning that all the
 services in the supervision tree have been started and are ready, you cannot rely
 on this option. </li>
+ <li> <tt>-X&nbsp;<em>consoleholder</em></tt>&nbsp;: assume the output console is available
+on descriptor <em>consoleholder</em>. If this option is given, and a <tt>s6-svscan-log</tt>
+service exists, the <a href="s6-supervise.html">s6-supervise</a> process for that service
+will be run with <em>consoleholder</em> as its standard error. This is mainly useful
+for a setup done via <a href="//skarnet.org/software/s6-linux-init/">s6-linux-init</a>,
+where all error messages go to the <tt>s6-svscan-log</tt> catch-all logger service by
+default, except messages from this service itself, which fall back to <em>consoleholder</em>.
+If you're not sure what to use this option for, or how, you don't need it. </li>
  <li> <tt>-c&nbsp;<em>max</em></tt>&nbsp;: maintain services for up to <em>max</em>
 service directories. Default is 500. Lower limit is 2. There is no upper limit, but:
  <ul>
diff --git a/doc/upgrade.html b/doc/upgrade.html
index d3ce8ef..e876665 100644
--- a/doc/upgrade.html
+++ b/doc/upgrade.html
@@ -28,6 +28,9 @@ disabled when execline support is disabled. </li>
  <li> A new '?' directive has been added to <a href="s6-log.html">s6-log</a>,
 it declares a processor command line that is spawned with the <tt>/bin/sh</tt>
 interpreter. </li>
+ <li> A new <tt>-X</tt> option has been added to <a href="s6-svscan.html>s6-svscan</a>
+to better support <a href="//skarnet.org/software/s6-linux-init/">s6-linux-init</a>
+installations. </li>
 </ul>
 
 <h2> in 2.9.0.1 </h2>
diff --git a/src/supervision/s6-svscan.c b/src/supervision/s6-svscan.c
index ffc257d..c818498 100644
--- a/src/supervision/s6-svscan.c
+++ b/src/supervision/s6-svscan.c
@@ -21,13 +21,14 @@
 #include <s6/config.h>
 #include <s6/s6-supervise.h>
 
-#define USAGE "s6-svscan [ -S | -s ] [ -c maxservices ] [ -t timeout ] [ -d notif ] [ dir ]"
+#define USAGE "s6-svscan [ -S | -s ] [ -c maxservices ] [ -t timeout ] [ -d notif ] [ -X consoleholder ] [ dir ]"
 #define dieusage() strerr_dieusage(100, USAGE)
 
 #define FINISH_PROG S6_SVSCAN_CTLDIR "/finish"
 #define CRASH_PROG S6_SVSCAN_CTLDIR "/crash"
 #define SIGNAL_PROG S6_SVSCAN_CTLDIR "/SIG"
 #define SIGNAL_PROG_LEN (sizeof(SIGNAL_PROG) - 1)
+#define SPECIAL_LOGGER_SERVICE "s6-svscan-log"
 
 #define DIR_RETRY_TIMEOUT 3
 #define CHECK_RETRY_TIMEOUT 4
@@ -52,6 +53,7 @@ static int wantreap = 1 ;
 static int wantscan = 1 ;
 static unsigned int wantkill = 0 ;
 static int cont = 1 ;
+static unsigned int consoleholder = 0 ;
 
 static void panicnosp (char const *) gccattr_noreturn ;
 static void panicnosp (char const *errmsg)
@@ -298,6 +300,10 @@ static void trystart (unsigned int i, char const *name, int islog)
       if (services[i].flaglog)
         if (fd_move(!islog, services[i].p[!islog]) == -1)
           strerr_diefu2sys(111, "set fds for ", name) ;
+      if (consoleholder
+       && !strcmp(name, SPECIAL_LOGGER_SERVICE)
+       && fd_move(2, consoleholder) < 0)  /* autoclears coe */
+         strerr_diefu1sys(111, "restore console fd for service " SPECIAL_LOGGER_SERVICE) ;
       xpathexec_run(S6_BINPREFIX "s6-supervise", cargv, (char const **)environ) ;
     }
   }
@@ -458,7 +464,7 @@ int main (int argc, char const *const *argv)
     unsigned int t = 0 ;
     for (;;)
     {
-      int opt = subgetopt_r(argc, argv, "Sst:c:d:", &l) ;
+      int opt = subgetopt_r(argc, argv, "Sst:c:d:X:", &l) ;
       if (opt == -1) break ;
       switch (opt)
       {
@@ -471,6 +477,11 @@ int main (int argc, char const *const *argv)
           if (notif < 3) strerr_dief1x(100, "notification fd must be 3 or more") ;
           if (fcntl(notif, F_GETFD) < 0) strerr_dief1sys(100, "invalid notification fd") ;
           break ;
+        case 'X' :
+          if (!uint0_scan(l.arg, &consoleholder)) dieusage() ;
+          if (consoleholder < 3) strerr_dief1x(100, "console holder fd must be 3 or more") ;
+          if (fcntl(consoleholder, F_GETFD) < 0) strerr_dief1sys(100, "invalid console holder fd") ;
+          break ;
         default : dieusage() ;
       }
     }
@@ -487,6 +498,7 @@ int main (int argc, char const *const *argv)
   */
 
   if (argc && (chdir(argv[0]) < 0)) strerr_diefu1sys(111, "chdir") ;
+  if (consoleholder && coe(consoleholder) < 0) strerr_diefu1sys(111, "coe console holder") ;
   x[1].fd = s6_supervise_lock(S6_SVSCAN_CTLDIR) ;
   x[0].fd = selfpipe_init() ;
   if (x[0].fd < 0) strerr_diefu1sys(111, "selfpipe_init") ;
@@ -509,7 +521,6 @@ int main (int argc, char const *const *argv)
     }
     if (selfpipe_trapset(&set) < 0) strerr_diefu1sys(111, "trap signals") ;
   }
-
   if (notif)
   {
     fd_write(notif, "\n", 1) ;