Add process group management functionality to s6-setsid

2 files changed, 89 insertions, 24 deletions

diff --git a/doc/s6-setsid.html b/doc/s6-setsid.html
index 2fe991b..d5046af 100644
--- a/doc/s6-setsid.html
+++ b/doc/s6-setsid.html
@@ -18,29 +18,58 @@
 <h1> The s6-setsid program </h1>
 
 <p>
-s6-setsid runs a program as session leader.
+ s6-setsid runs a program as a new session leader, or in a new
+foreground or background process group.
 </p>
 
 <h2> Interface </h2>
 
 <pre>
-     s6-setsid [ -I | -i ] <em>prog...</em>
+     s6-setsid [ -s | -b | -f | -g ] [ -i | -I | -q ] [ -d ctty ] <em>prog...</em>
 </pre>
 
 <ul>
- <li> s6-setsid creates a new session if it is not a session leader, and becomes
-session leader of this new session. </li>
- <li> It then executes into <em>prog...</em>. </li>
+ <li> s6-setsid creates a new session, or a new process group,
+and may make that process group the foreground process group,
+depending on the options it has been given. </li>
+ <li> As session leader or process group leader, s6-setsid then
+executes into <em>prog...</em>. </li>
 </ul>
 
 <h2> Options </h2>
 
 <ul>
- <li> <tt>-i</tt>&nbsp;: strict. If s6-setsid is already a session leader, it will
-exit 111 with an error message. </li>
- <li> <tt>-I</tt>&nbsp;: loose. If s6-setsid is already a session leader, it will
-print a warning message, but exec into <em>prog</em> nonetheless. This is the
-default. </li>
+ <li> <tt>-s</tt>&nbsp;: session. s6-setsid will try and execute
+<em>prog</em> as a session leader. This is the default. </li>
+ <li> <tt>-b</tt>&nbsp;: background process group. s6-setsid will
+not create a new session, but will create a new process group, and
+try and execute <em>prog</em> as the new process group leader. </li>
+ <li> <tt>-f</tt>&nbsp;: foreground process group. s6-setsid will
+not create a new session, but will create a new process group and
+attach its session's controlling terminal to the new process group
+before executing <em>prog</em>. However, the new process group
+will likely be stopped, waiting for the former foreground process
+group to relinquish the controlling terminal, and will need to be
+sent a SIGCONT to resume. To avoid that, use the next option. </li>
+ <li> <tt>-g</tt>&nbsp;: grab terminal. s6-setsid will
+not create a new session, but will create a new process group and
+attach its session's controlling terminal to the new process group
+before executing <em>prog</em>. It will forcefully grab the controlling
+terminal from the former foreground process group, which means that
+a process belonging to the former foreground process group attempting
+to read from or write to that terminal will be stopped. </li>
+ <li> <tt>-i</tt>&nbsp;: strict. If s6-setsid cannot perform the
+operations it needs, it will exit 111 with an error message. </li>
+ <li> <tt>-I</tt>&nbsp;: loose. If s6-setsid cannot perform the operations,
+it will print a warning message, but exec into <em>prog</em> nonetheless.
+This is the default. </li>
+ <li> <tt>-q</tt>&nbsp;: silent. s6-setsid will not print any warning
+message; it will exec into <em>prog</em> even if it cannot perform the
+operations. </li>
+ <li> <tt>-d&nbsp;<em>ctty</em></tt>&nbsp;: assume <em>ctty</em> is
+the controlling terminal for the current session. Default is 0.
+This is only useful when used with the <tt>-f</tt> or
+<tt>-g</tt> options. </li>
 </ul>
 
 </body>
diff --git a/src/daemontools-extras/s6-setsid.c b/src/daemontools-extras/s6-setsid.c
index efd3832..51de048 100644
--- a/src/daemontools-extras/s6-setsid.c
+++ b/src/daemontools-extras/s6-setsid.c
@@ -1,35 +1,71 @@
 /* ISC license. */
 
 #include <unistd.h>
+#include <signal.h>
+#include <skalibs/uint.h>
 #include <skalibs/sgetopt.h>
 #include <skalibs/strerr2.h>
+#include <skalibs/sig.h>
 #include <skalibs/djbunix.h>
 
-#define USAGE "s6-setsid [ -i | -I ] prog..."
+#define USAGE "s6-setsid [ -s | -b | -f | -g ] [ -i | -I | -q ] [ -d ctty ] prog..."
+#define dieusage() strerr_dieusage(100, USAGE)
 
 int main (int argc, char const *const *argv, char const *const *envp)
 {
-  int insist = 0 ;
+  unsigned int ctty = 0, what = 0, insist = 1 ;
   PROG = "s6-setsid" ;
-  for (;;)
   {
-    register int opt = subgetopt(argc, argv, "iI") ;
-    if (opt == -1) break ;
-    switch (opt)
+    subgetopt_t l = SUBGETOPT_ZERO ;
+    for (;;)
     {
-      case 'i' : insist = 1 ; break ;
-      case 'I' : insist = 0 ; break ;
-      default : strerr_dieusage(100, USAGE) ;
+      register int opt = subgetopt_r(argc, argv, "sbfgiIqt:", &l) ;
+      if (opt == -1) break ;
+      switch (opt)
+      {
+        case 's' : what = 0 ; break ;
+        case 'b' : what = 1 ; break ;
+        case 'f' : what = 2 ; break ;
+        case 'g' : what = 3 ; break ;
+        case 'i' : insist = 2 ; break ;
+        case 'I' : insist = 1 ; break ;
+        case 'q' : insist = 0 ; break ;
+        case 't' : if (!uint0_scan(l.arg, &ctty)) dieusage() ; break ;
+        default : dieusage() ;
+      }
     }
+    argc -= l.ind ; argv += l.ind ;
   }
-  argc -= subgetopt_here.ind ; argv += subgetopt_here.ind ;
-  if (!argc) strerr_dieusage(100, USAGE) ;
+  if (!argc) dieusage() ;
 
-  if (setsid() < 0)
+  if (what)
   {
-    if (insist) strerr_diefu1sys(111, "setsid") ;
-    else strerr_warnwu1sys("setsid") ;
+    if (setpgid(0, 0) < 0) switch (insist)
+    {
+      case 2 : strerr_diefu1sys(111, "setpgid") ;
+      case 1 : strerr_warnwu1sys("setpgid") ; break ;
+      default : break ;
+    }
+
+    if (what >= 2)
+    {
+      if (what == 3) sig_ignore(SIGTTOU) ;
+      if (tcsetpgrp(ctty, getpid()) < 0) switch (insist)
+      {
+        case 2 : strerr_diefu1sys(111, "tcsetpgrp") ;
+        case 1 : strerr_warnwu1sys("tcsetpgrp") ; break ;
+        default : break ;
+      }
+      if (what == 3) sig_restore(SIGTTOU) ;
+    }
+  }
+  else if (setsid() < 0) switch (insist)
+  {
+    case 2 : strerr_diefu1sys(111, "setsid") ;
+    case 1 : strerr_warnwu1sys("setsid") ; break ;
+    default : break ;
   }
+
   pathexec_run(argv[0], argv, envp) ;
   strerr_dieexec(111, argv[0]) ;
 }