setsid: code shrink, expanded comments

function                                             old     new   delta
setsid_main                                           56      53      -3

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/miscutils/setsid.c b/miscutils/setsid.c
index ad2c8a4de..637081b6c 100644
--- a/miscutils/setsid.c
+++ b/miscutils/setsid.c
@@ -31,7 +31,17 @@ int setsid_main(int argc UNUSED_PARAM, char **argv)
 
         /* setsid() is allowed only when we are not a process group leader.
          * Otherwise our PID serves as PGID of some existing process group
-         * and cannot be used as PGID of a new process group. */
+         * and cannot be used as PGID of a new process group.
+         *
+         * Example: setsid() below fails when run alone in interactive shell:
+         *  $ setsid PROG
+         * because shell's child (setsid) is put in a new process group.
+         * But doesn't fail if shell is not interactive
+         * (and therefore doesn't create process groups for pipes),
+         * or if setsid is not the first process in the process group:
+         *  $ true | setsid PROG
+         * or if setsid is executed in backquotes (`setsid PROG`)...
+         */
         if (setsid() < 0) {
                 pid_t pid = fork_or_rexec(argv);
                 if (pid != 0) {
@@ -43,7 +53,7 @@ int setsid_main(int argc UNUSED_PARAM, char **argv)
                          * However, the code is larger and upstream
                          * does not do such trick.
                          */
-                        exit(EXIT_SUCCESS);
+                        return EXIT_SUCCESS;
                 }
 
                 /* child */