hush: make it possible to have interactive shell on non-ctty.

 init=/bin/hush: shows prompt, history works, etc.

function                                             old     new   delta
hush_main                                            888     925     +37
block_signals                                        139     152     +13
builtin_fg_bg                                        284     293      +9
checkjobs_and_fg_shell                                35      41      +6
sigexit                                               65      66      +1
reset_traps_to_defaults                              165     164      -1
parse_stream                                        2200    2184     -16
run_list                                            2502    2475     -27
getpgid                                               35       -     -35
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 5/3 up/down: 66/-79)            Total: -13 bytes

1 files changed, 80 insertions, 58 deletions

diff --git a/shell/hush.c b/shell/hush.c
index d0819f691..45a9733cf 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -417,15 +417,26 @@ struct function {
 /* "Globals" within this file */
 /* Sorted roughly by size (smaller offsets == smaller code) */
 struct globals {
+        /* interactive_fd != 0 means we are an interactive shell.
+         * If we are, then saved_tty_pgrp can also be != 0, meaning
+         * that controlling tty is available. With saved_tty_pgrp == 0,
+         * job control still works, but terminal signals
+         * (^C, ^Z, ^Y, ^\) won't work at all, and background
+         * process groups can only be created with "cmd &".
+         * With saved_tty_pgrp != 0, hush will use tcsetpgrp()
+         * to give tty to the foreground process group,
+         * and will take it back when the group is stopped (^Z)
+         * or killed (^C).
+         */
 #if ENABLE_HUSH_INTERACTIVE
         /* 'interactive_fd' is a fd# open to ctty, if we have one
          * _AND_ if we decided to act interactively */
         int interactive_fd;
         const char *PS1;
         const char *PS2;
-#define G_interactive_fd (G.interactive_fd)
+# define G_interactive_fd (G.interactive_fd)
 #else
-#define G_interactive_fd 0
+# define G_interactive_fd 0
 #endif
 #if ENABLE_FEATURE_EDITING
         line_input_t *line_input_state;
@@ -434,10 +445,9 @@ struct globals {
         pid_t last_bg_pid;
 #if ENABLE_HUSH_JOB
         int run_list_level;
-        pid_t saved_tty_pgrp;
         int last_jobid;
+        pid_t saved_tty_pgrp;
         struct pipe *job_list;
-        struct pipe *toplevel_list;
 #endif
         smallint flag_SIGINT;
 #if ENABLE_HUSH_LOOPS
@@ -446,7 +456,7 @@ struct globals {
 #if ENABLE_HUSH_FUNCTIONS
         /* 0: outside of a function (or sourced file)
          * -1: inside of a function, ok to use return builtin
-         * 1: return is invoked, skip all till end of func.
+         * 1: return is invoked, skip all till end of func
          */
         smallint flag_return_in_progress;
 #endif
@@ -1089,12 +1099,16 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  */
 enum {
         SPECIAL_INTERACTIVE_SIGS = 0
-#if ENABLE_HUSH_JOB
-                | (1 << SIGTTIN) | (1 << SIGTTOU) | (1 << SIGTSTP)
-                | (1 << SIGHUP)
-#endif
                 | (1 << SIGTERM)
                 | (1 << SIGINT)
+                | (1 << SIGHUP)
+                ,
+#if ENABLE_HUSH_JOB
+        SPECIAL_JOB_SIGS = 0
+                | (1 << SIGTTIN)
+                | (1 << SIGTTOU)
+                | (1 << SIGTSTP)
+#endif
 };
 
 //static void SIGCHLD_handler(int sig UNUSED_PARAM)
@@ -1122,7 +1136,7 @@ static void sigexit(int sig)
 
         /* Careful: we can end up here after [v]fork. Do not restore
          * tty pgrp then, only top-level shell process does that */
-        if (G_interactive_fd && getpid() == G.root_pid)
+        if (G.saved_tty_pgrp && getpid() == G.root_pid)
                 tcsetpgrp(G_interactive_fd, G.saved_tty_pgrp);
 
         /* Not a signal, just exit */
@@ -3131,7 +3145,7 @@ static const char *get_cmdtext(struct pipe *pi)
                 len += strlen(*argv) + 1;
         } while (*++argv);
         p = xmalloc(len);
-        pi->cmdtext = p;// = xmalloc(len);
+        pi->cmdtext = p;
         argv = pi->cmds[0].argv;
         do {
                 len = strlen(*argv);
@@ -3351,10 +3365,12 @@ static int checkjobs_and_fg_shell(struct pipe* fg_pipe)
 {
         pid_t p;
         int rcode = checkjobs(fg_pipe);
-        /* Job finished, move the shell to the foreground */
-        p = getpgid(0); /* pgid of our process */
-        debug_printf_jobs("fg'ing ourself: getpgid(0)=%d\n", (int)p);
-        tcsetpgrp(G_interactive_fd, p);
+        if (G.saved_tty_pgrp) {
+                /* Job finished, move the shell to the foreground */
+                p = getpgrp(); /* our process group id */
+                debug_printf_jobs("fg'ing ourself: getpgrp()=%d\n", (int)p);
+                tcsetpgrp(G_interactive_fd, p);
+        }
         return rcode;
 }
 #endif
@@ -3606,7 +3622,10 @@ static int run_pipe(struct pipe *pi)
                                 pgrp = pi->pgrp;
                                 if (pgrp < 0) /* true for 1st process only */
                                         pgrp = getpid();
-                                if (setpgid(0, pgrp) == 0 && pi->followup != PIPE_BG) {
+                                if (setpgid(0, pgrp) == 0
+                                 && pi->followup != PIPE_BG
+                                 && G.saved_tty_pgrp /* we have ctty */
+                                ) {
                                         /* We do it in *every* child, not just first,
                                          * to avoid races */
                                         tcsetpgrp(G_interactive_fd, pgrp);
@@ -4023,11 +4042,7 @@ static int run_list(struct pipe *pi)
                                 check_and_run_traps(0);
 #if ENABLE_HUSH_JOB
                                 if (G.run_list_level == 1)
-{
-debug_printf_exec("insert_bg_job1\n");
                                         insert_bg_job(pi);
-debug_printf_exec("insert_bg_job2\n");
-}
 #endif
                                 G.last_exitcode = rcode = EXIT_SUCCESS;
                                 debug_printf_exec(": cmd&: exitcode EXIT_SUCCESS\n");
@@ -5896,8 +5911,11 @@ static void block_signals(int second_time)
         unsigned mask;
 
         mask = (1 << SIGQUIT);
-        if (G_interactive_fd)
+        if (G_interactive_fd) {
                 mask = (1 << SIGQUIT) | SPECIAL_INTERACTIVE_SIGS;
+                if (G.saved_tty_pgrp) /* we have ctty, job control sigs work */
+                        mask |= SPECIAL_JOB_SIGS;
+        }
         G.non_DFL_mask = mask;
 
         if (!second_time)
@@ -6179,52 +6197,55 @@ int hush_main(int argc, char **argv)
         if (isatty(STDIN_FILENO) && isatty(STDOUT_FILENO)) {
                 G.saved_tty_pgrp = tcgetpgrp(STDIN_FILENO);
                 debug_printf("saved_tty_pgrp:%d\n", G.saved_tty_pgrp);
-//TODO: "interactive" and "have job control" are two different things.
-//If tcgetpgrp fails here, "have job control" is false, but "interactive"
-//should stay on! Currently, we mix these into one.
-                if (G.saved_tty_pgrp >= 0) {
-                        /* try to dup stdin to high fd#, >= 255 */
-                        G_interactive_fd = fcntl(STDIN_FILENO, F_DUPFD, 255);
+                if (G.saved_tty_pgrp < 0)
+                        G.saved_tty_pgrp = 0;
+
+                /* try to dup stdin to high fd#, >= 255 */
+                G_interactive_fd = fcntl(STDIN_FILENO, F_DUPFD, 255);
+                if (G_interactive_fd < 0) {
+                        /* try to dup to any fd */
+                        G_interactive_fd = dup(STDIN_FILENO);
                         if (G_interactive_fd < 0) {
-                                /* try to dup to any fd */
-                                G_interactive_fd = dup(STDIN_FILENO);
-                                if (G_interactive_fd < 0)
-                                        /* give up */
-                                        G_interactive_fd = 0;
+                                /* give up */
+                                G_interactive_fd = 0;
+                                G.saved_tty_pgrp = 0;
                         }
-// TODO: track & disallow any attempts of user
-// to (inadvertently) close/redirect it
                 }
+// TODO: track & disallow any attempts of user
+// to (inadvertently) close/redirect G_interactive_fd
         }
         debug_printf("interactive_fd:%d\n", G_interactive_fd);
         if (G_interactive_fd) {
-                pid_t shell_pgrp;
-
-                /* We are indeed interactive shell, and we will perform
-                 * job control. Setting up for that. */
-
                 close_on_exec_on(G_interactive_fd);
-                /* 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) {
-                        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);
+
+                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);
+                        }
                 }
+
                 /* Block some signals */
                 block_signals(signal_mask_is_inited);
-                /* Set other signals to restore saved_tty_pgrp */
-                set_fatal_handlers();
-                /* Put ourselves in our own process group */
-                bb_setpgrp(); /* is the same as setpgid(our_pid, our_pid); */
-                /* Grab control of the terminal */
-                tcsetpgrp(G_interactive_fd, getpid());
+
+                if (G.saved_tty_pgrp) {
+                        /* Set other signals to restore saved_tty_pgrp */
+                        set_fatal_handlers();
+                        /* 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, getpid());
+                }
                 /* -1 is special - makes xfuncs longjmp, not exit
                  * (we reset die_sleep = 0 whereever we [v]fork) */
                 enable_restore_tty_pgrp_on_exit(); /* sets die_sleep = -1 */
@@ -6604,6 +6625,7 @@ static int builtin_fg_bg(char **argv)
 
         if (!G_interactive_fd)
                 return EXIT_FAILURE;
+
         /* If they gave us no args, assume they want the last backgrounded task */
         if (!argv[1]) {
                 for (pi = G.job_list; pi; pi = pi->next) {
@@ -6628,7 +6650,7 @@ static int builtin_fg_bg(char **argv)
  found:
         /* TODO: bash prints a string representation
          * of job being foregrounded (like "sleep 1 | cat") */
-        if (argv[0][0] == 'f') {
+        if (argv[0][0] == 'f' && G.saved_tty_pgrp) {
                 /* Put the job into the foreground.  */
                 tcsetpgrp(G_interactive_fd, pi->pgrp);
         }