Bash-5.0 patch 5: prevent optimizing forks away too aggressively

Author: Chet Ramey

builtins/evalstring.c

@@ -100,12 +100,22 @@ should_suppress_fork (command)
 	  ((command->flags & CMD_INVERT_RETURN) == 0));
 }
 
+int
+can_optimize_connection (command)
+     COMMAND *command;
+{
+  return (*bash_input.location.string == '\0' &&
+	  (command->value.Connection->connector == AND_AND || command->value.Connection->connector == OR_OR || command->value.Connection->connector == ';') &&
+	  command->value.Connection->second->type == cm_simple);
+}
+
 void
 optimize_fork (command)
      COMMAND *command;
 {
   if (command->type == cm_connection &&
-      (command->value.Connection->connector == AND_AND || command->value.Connection->connector == OR_OR) &&
+      (command->value.Connection->connector == AND_AND || command->value.Connection->connector == OR_OR || command->value.Connection->connector == ';') &&
+      (command->value.Connection->second->flags & CMD_TRY_OPTIMIZING) &&
       should_suppress_fork (command->value.Connection->second))
     {
       command->value.Connection->second->flags |= CMD_NO_FORK;
@@ -412,8 +422,18 @@ parse_and_execute (string, from_file, flags)
 		  command->flags |= CMD_NO_FORK;
 		  command->value.Simple->flags |= CMD_NO_FORK;
 		}
-	      else if (command->type == cm_connection)
-		optimize_fork (command);
+
+	      /* Can't optimize forks out here execept for simple commands.
+		 This knows that the parser sets up commands as left-side heavy
+		 (&& and || are left-associative) and after the single parse,
+		 if we are at the end of the command string, the last in a
+		 series of connection commands is
+		 command->value.Connection->second. */
+	      else if (command->type == cm_connection && can_optimize_connection (command))
+		{
+		  command->value.Connection->second->flags |= CMD_TRY_OPTIMIZING;
+		  command->value.Connection->second->value.Simple->flags |= CMD_TRY_OPTIMIZING;
+		}
 #endif /* ONESHOT */
 
 	      /* See if this is a candidate for $( <file ). */

command.h

@@ -186,6 +186,7 @@ typedef struct element {
 #define CMD_COPROC_SUBSHELL 0x1000
 #define CMD_LASTPIPE	    0x2000
 #define CMD_STDPATH	    0x4000	/* use standard path for command lookup */
+#define CMD_TRY_OPTIMIZING  0x8000	/* try to optimize this simple command */
 
 /* What a command looks like. */
 typedef struct command {

execute_cmd.c

@@ -2767,6 +2767,8 @@ execute_connection (command, asynchronous, pipe_in, pipe_out, fds_to_close)
 	  ((command->value.Connection->connector == OR_OR) &&
 	   (exec_result != EXECUTION_SUCCESS)))
 	{
+	  optimize_fork (command);
+
 	  second = command->value.Connection->second;
 	  if (ignore_return && second)
 	    second->flags |= CMD_IGNORE_RETURN;

patchlevel.h

@@ -25,6 +25,6 @@
    regexp `^#define[ 	]*PATCHLEVEL', since that's what support/mkversion.sh
    looks for to find the patch level (for the sccs version string). */
 
-#define PATCHLEVEL 4
+#define PATCHLEVEL 5
 
 #endif /* _PATCHLEVEL_H_ */