hush: fix SIGCHLD counting code, but keep it disabled for now.

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

1 files changed, 66 insertions, 19 deletions

diff --git a/shell/hush.c b/shell/hush.c
index acc8ef944..fd839d061 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -69,7 +69,7 @@
 #endif
 
 
-/* Debug build knobs */
+/* Build knobs */
 #define LEAK_HUNTING 0
 #define BUILD_AS_NOMMU 0
 /* Enable/disable sanity checks. Ok to enable in production,
@@ -77,6 +77,13 @@
  * Keeping 1 for now even in released versions.
  */
 #define HUSH_DEBUG 1
+/* Slightly bigger (+200 bytes), but faster hush.
+ * So far it only enables a trick with counting SIGCHLDs and forks,
+ * which allows us to do fewer waitpid's.
+ * (we can detect a case where neither forks were done nor SIGCHLDs happened
+ * and therefore waitpid will return the same result as last time)
+ */
+#define ENABLE_HUSH_FAST 0
 
 
 #if BUILD_AS_NOMMU
@@ -485,8 +492,11 @@ struct globals {
         struct function *top_func;
 #endif
         /* Signal and trap handling */
-//      unsigned count_SIGCHLD;
-//      unsigned handled_SIGCHLD;
+#if ENABLE_HUSH_FAST
+        unsigned count_SIGCHLD;
+        unsigned handled_SIGCHLD;
+        smallint last_waitpid_was_0;
+#endif
         /* which signals have non-DFL handler (even with no traps set)? */
         unsigned non_DFL_mask;
         char **traps; /* char *traps[NSIG] */
@@ -1050,7 +1060,7 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  *    Restore blocked signal set to one inherited by shell just prior to exec.
  *
  * Note: as a result, we do not use signal handlers much. The only uses
- * are to count SIGCHLDs [disabled - bug somewhere, + bloat]
+ * are to count SIGCHLDs
  * and to restore tty pgrp on signal-induced exit.
  */
 enum {
@@ -1067,10 +1077,13 @@ enum {
 #endif
 };
 
-//static void SIGCHLD_handler(int sig UNUSED_PARAM)
-//{
-//      G.count_SIGCHLD++;
-//}
+#if ENABLE_HUSH_FAST
+static void SIGCHLD_handler(int sig UNUSED_PARAM)
+{
+        G.count_SIGCHLD++;
+//bb_error_msg("[%d] SIGCHLD_handler: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
+}
+#endif
 
 #if ENABLE_HUSH_JOB
 
@@ -1158,9 +1171,12 @@ static int check_and_run_traps(int sig)
                 }
                 /* not a trap: special action */
                 switch (sig) {
-//              case SIGCHLD:
-//                      G.count_SIGCHLD++;
-//                      break;
+#if ENABLE_HUSH_FAST
+                case SIGCHLD:
+                        G.count_SIGCHLD++;
+//bb_error_msg("[%d] check_and_run_traps: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
+                        break;
+#endif
                 case SIGINT:
                         /* Builtin was ^C'ed, make it look prettier: */
                         bb_putchar('\n');
@@ -2665,6 +2681,10 @@ static void setup_heredoc(struct redir_struct *redir)
 #endif
         }
         /* parent */
+#if ENABLE_HUSH_FAST
+        G.count_SIGCHLD++;
+//bb_error_msg("[%d] fork in setup_heredoc: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
+#endif
         enable_restore_tty_pgrp_on_exit();
 #if !BB_MMU
         free(to_free);
@@ -3273,9 +3293,16 @@ static int checkjobs(struct pipe* fg_pipe)
         debug_printf_jobs("checkjobs %p\n", fg_pipe);
 
         errno = 0;
-//      if (G.handled_SIGCHLD == G.count_SIGCHLD)
-//              /* avoid doing syscall, nothing there anyway */
-//              return rcode;
+#if ENABLE_HUSH_FAST
+        if (G.handled_SIGCHLD == G.count_SIGCHLD) {
+//bb_error_msg("[%d] checkjobs: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d was 0?:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD, G.last_waitpid_was_0);
+                /* avoid doing syscall, nothing there anyway */
+                if (G.last_waitpid_was_0)
+                        return 0;
+                errno = ECHILD;
+                return -1;
+        }
+#endif
 
         attributes = WUNTRACED;
         if (fg_pipe == NULL)
@@ -3294,13 +3321,20 @@ static int checkjobs(struct pipe* fg_pipe)
                 int i;
                 int dead;
 
-//              i = G.count_SIGCHLD;
+#if ENABLE_HUSH_FAST
+                i = G.count_SIGCHLD;
+#endif
                 childpid = waitpid(-1, &status, attributes);
                 if (childpid <= 0) {
                         if (childpid && errno != ECHILD)
                                 bb_perror_msg("waitpid");
-//                      else /* Until next SIGCHLD, waitpid's are useless */
-//                              G.handled_SIGCHLD = i;
+#if ENABLE_HUSH_FAST
+                        else { /* Until next SIGCHLD, waitpid's are useless */
+                                G.last_waitpid_was_0 = (childpid == 0);
+                                G.handled_SIGCHLD = i;
+//bb_error_msg("[%d] checkjobs: waitpid returned <= 0, G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
+                        }
+#endif
                         break;
                 }
                 dead = WIFEXITED(status) || WIFSIGNALED(status);
@@ -3696,6 +3730,10 @@ static int run_pipe(struct pipe *pi)
                 }
 
                 /* parent or error */
+#if ENABLE_HUSH_FAST
+                G.count_SIGCHLD++;
+//bb_error_msg("[%d] fork in run_pipe: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
+#endif
                 enable_restore_tty_pgrp_on_exit();
 #if !BB_MMU
                 /* Clean up after vforked child */
@@ -4861,6 +4899,10 @@ static FILE *generate_stream_from_string(const char *s)
         }
 
         /* parent */
+#if ENABLE_HUSH_FAST
+        G.count_SIGCHLD++;
+//bb_error_msg("[%d] fork in generate_stream_from_string: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
+#endif
         enable_restore_tty_pgrp_on_exit();
 #if !BB_MMU
         free(to_free);
@@ -5990,9 +6032,14 @@ static void block_signals(int second_time)
                         second_time ? NULL : &G.inherited_set);
         /* POSIX allows shell to re-enable SIGCHLD
          * even if it was SIG_IGN on entry */
-//      G.count_SIGCHLD++; /* ensure it is != G.handled_SIGCHLD */
+#if ENABLE_HUSH_FAST
+        G.count_SIGCHLD++; /* ensure it is != G.handled_SIGCHLD */
+        if (!second_time)
+                signal(SIGCHLD, SIGCHLD_handler);
+#else
         if (!second_time)
-                signal(SIGCHLD, SIG_DFL); // SIGCHLD_handler);
+                signal(SIGCHLD, SIG_DFL);
+#endif
 }
 
 #if ENABLE_HUSH_JOB