hush: disentangle interactiveness/job_control setup code

...and discover that we can do away with 1-3 initialization syscalls.

function                                             old     new   delta
hush_main                                           1152    1146      -6

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

1 files changed, 67 insertions, 79 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 98812b507..debae4d58 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -10790,100 +10790,86 @@ int hush_main(int argc, char **argv)
 
         /* A shell is interactive if the '-i' flag was given,
          * or if all of the following conditions are met:
-         *    no -c command
-         *    no arguments remaining or the -s flag given
+         *    not -c 'CMD'
+         *    not running a script (no arguments remaining, or -s flag given)
          *    standard input is a terminal
          *    standard output is a terminal
          * Refer to Posix.2, the description of the 'sh' utility.
          */
-#if ENABLE_HUSH_JOB
-        if (!G_reexeced_on_NOMMU
-         && isatty(STDIN_FILENO) && isatty(STDOUT_FILENO)
-        ) {
-                G_saved_tty_pgrp = tcgetpgrp(STDIN_FILENO);
-                debug_printf("saved_tty_pgrp:%d\n", G_saved_tty_pgrp);
-                if (G_saved_tty_pgrp < 0)
-                        G_saved_tty_pgrp = 0;
-
-                /* try to dup stdin to high fd#, >= 255 */
-                G_interactive_fd = dup_CLOEXEC(STDIN_FILENO, 254);
-                if (G_interactive_fd < 0) {
-                        /* try to dup to any fd */
-                        G_interactive_fd = dup_CLOEXEC(STDIN_FILENO, -1);
-                        if (G_interactive_fd < 0) {
-                                /* give up */
-                                G_interactive_fd = 0;
-                                G_saved_tty_pgrp = 0;
-                        }
-                }
-        }
-        debug_printf("interactive_fd:%d\n", G_interactive_fd);
-        if (G_interactive_fd) {
-                if (G_saved_tty_pgrp) {
-                        /* If we were run as 'hush &', sleep until we are
-                         * in the foreground (tty pgrp == our pgrp).
-                         * If we get started under a job aware app (like bash),
-                         * make sure we are now in charge so we don't fight over
-                         * who gets the foreground */
-                        while (1) {
-                                pid_t shell_pgrp = getpgrp();
-                                G_saved_tty_pgrp = tcgetpgrp(G_interactive_fd);
-                                if (G_saved_tty_pgrp == shell_pgrp)
-                                        break;
-                                /* send TTIN to ourself (should stop us) */
-                                kill(- shell_pgrp, SIGTTIN);
-                        }
-                }
-
-                /* Install more signal handlers */
-                install_special_sighandlers();
-
-                if (G_saved_tty_pgrp) {
-                        /* Set fatal signals to restore saved_tty_pgrp */
-                        install_fatal_sighandlers();
-                        /* Put ourselves in our own process group
-                         * (bash, too, does this only if ctty is available) */
-                        bb_setpgrp(); /* is the same as setpgid(our_pid, our_pid); */
-                        /* Grab control of the terminal */
-                        tcsetpgrp(G_interactive_fd, G.root_pid);
-                }
-                init_line_editing();
-        }
-#elif ENABLE_HUSH_INTERACTIVE
-        /* No job control compiled in, only prompt/line editing */
+#if ENABLE_HUSH_INTERACTIVE
         if (!G_reexeced_on_NOMMU
          && isatty(STDIN_FILENO) && isatty(STDOUT_FILENO)
         ) {
+                /* Try to dup stdin to high fd#, >= 255 */
                 G_interactive_fd = dup_CLOEXEC(STDIN_FILENO, 254);
                 if (G_interactive_fd < 0) {
-                        /* try to dup to any fd */
+                        /* Try to dup to any fd */
                         G_interactive_fd = dup_CLOEXEC(STDIN_FILENO, -1);
                         if (G_interactive_fd < 0)
-                                /* give up */
+                                /* Give up */
                                 G_interactive_fd = 0;
                 }
+                debug_printf("interactive_fd:%d\n", G_interactive_fd);
                 if (G_interactive_fd) {
+// TODO? bash:
+// if interactive but not a login shell, sources ~/.bashrc
+// (--norc turns this off, --rcfile <file> overrides)
+# if ENABLE_HUSH_JOB
+                        /* Can we do job control? */
+                        G_saved_tty_pgrp = tcgetpgrp(G_interactive_fd);
+                        debug_printf("saved_tty_pgrp:%d\n", G_saved_tty_pgrp);
+                        if (G_saved_tty_pgrp < 0)
+                                G_saved_tty_pgrp = 0; /* no */
+                        if (G_saved_tty_pgrp) {
+                                /* If we were run as 'hush &', sleep until we are
+                                 * in the foreground (tty pgrp == our pgrp).
+                                 * If we get started under a job aware app (like bash),
+                                 * make sure we are now in charge so we don't fight over
+                                 * who gets the foreground */
+                                while (1) {
+                                        pid_t shell_pgrp = getpgrp();
+                                        if (G_saved_tty_pgrp == shell_pgrp) {
+/* Often both pgrps here are set to our pid - but not always!
+ * Example: sh -c 'echo $$; hush; echo FIN'
+ * Here, the parent shell is not interactive, so it does NOT set up
+ * a separate process group for its children, and we (hush) initinally
+ * run in parent's process group (until we set up our own a few lines down).
+ */
+                                                //bb_error_msg("process groups tty:%d hush:%d", G_saved_tty_pgrp, shell_pgrp);
+                                                break;
+                                        }
+                                        /* Send TTIN to ourself (should stop us) */
+                                        kill(- shell_pgrp, SIGTTIN);
+                                        G_saved_tty_pgrp = tcgetpgrp(G_interactive_fd);
+                                }
+                        }
+# endif
+                        /* Install more signal handlers */
                         install_special_sighandlers();
+# if ENABLE_HUSH_JOB
+                        if (G_saved_tty_pgrp) {
+                                /* Set fatal signals to restore saved_tty_pgrp */
+                                install_fatal_sighandlers();
+                                /* (The if() is an optimization: can avoid two redundant syscalls) */
+                                if (G_saved_tty_pgrp != G.root_pid) {
+                                        /* Put ourselves in our own process group
+                                         * (bash, too, does this only if ctty is available) */
+                                        bb_setpgrp(); /* is the same as setpgid(our_pid, our_pid); */
+                                        /* Grab control of the terminal */
+                                        tcsetpgrp(G_interactive_fd, G.root_pid);
+                                }
+                        }
+# endif
+# if ENABLE_FEATURE_EDITING_FANCY_PROMPT
+                        /* Set (but not export) PS1/2 unless already set */
+                        if (!get_local_var_value("PS1"))
+                                set_local_var_from_halves("PS1", "\\w \\$ ");
+                        if (!get_local_var_value("PS2"))
+                                set_local_var_from_halves("PS2", "> ");
+# endif
                         init_line_editing();
-                }
-        }
-#else
-        /* We have interactiveness code disabled */
-#endif
-        /* bash:
-         * if interactive but not a login shell, sources ~/.bashrc
-         * (--norc turns this off, --rcfile <file> overrides)
-         */
 
-        if (G_interactive_fd) {
-#if ENABLE_HUSH_INTERACTIVE && ENABLE_FEATURE_EDITING_FANCY_PROMPT
-                /* Set (but not export) PS1/2 unless already set */
-                if (!get_local_var_value("PS1"))
-                        set_local_var_from_halves("PS1", "\\w \\$ ");
-                if (!get_local_var_value("PS2"))
-                        set_local_var_from_halves("PS2", "> ");
-#endif
-                if (!ENABLE_FEATURE_SH_EXTRA_QUIET) {
+# if !ENABLE_FEATURE_SH_EXTRA_QUIET
                         /* note: ash and hush share this string */
                         printf("\n\n%s %s\n"
                                 IF_HUSH_HELP("Enter 'help' for a list of built-in commands.\n")
@@ -10891,8 +10877,10 @@ int hush_main(int argc, char **argv)
                                 bb_banner,
                                 "hush - the humble shell"
                         );
-                }
-        }
+# endif
+                } /* if become interactive */
+        } /* if on tty */
+#endif /* if INTERACTIVE is allowed by build config */
 
         parse_and_run_file(hfopen(NULL)); /* stdin */