[NTOS:KDBG] Small improvements for KdbpCliMainLoop() and KdbpDoCommand() (#4917)

- Move the printing pager state reset code (setting the number of
  printed rows and columns to zero, and the output aborted flag)
  to KdbpDoCommand(). This allows to keep the original behaviour,
  while also inheriting it whenever KdbpDoCommand() is invoked
  elsewhere (for example, from KdbpCliInterpretInitFile()).

- Use KdbPuts/Printf() instead of KdbpPrint() for the entry banners,
  so that they aren't subject to the current printing pager state.
  Do the same for the "command unknown" error in KdbpDoCommand().

- Add a "Type 'help' for a list of commands" banner, for the users.

- Replace the do-while-loop with a simple while-loop.

ntoskrnl/kdbg/kdb_cli.c

@@ -2910,7 +2910,7 @@ KdbpPagerInternal(
         KdpInitTerminal();
     }
 
-    /* Refresh terminal size each time when number of rows printed is 0 */
+    /* Refresh terminal size each time when number of printed rows is 0 */
     if (KdbNumberOfRowsPrinted == 0)
     {
         KdpUpdateTerminalSize(&KdTermSize);
@@ -3030,7 +3030,7 @@ KdbpPagerInternal(
             p[i + 1] = c;
 
         /* Set p to the start of the next line and
-         * remember the number of rows/cols printed */
+         * remember the number of printed rows/cols */
         p += i;
         if (p[0] == '\n')
         {
@@ -3205,6 +3205,7 @@ static BOOLEAN
 KdbpDoCommand(
     IN PCHAR Command)
 {
+    BOOLEAN Continue = TRUE;
     SIZE_T i;
     PCHAR p;
     ULONG Argc;
@@ -3238,6 +3239,10 @@ KdbpDoCommand(
     if (Argc < 1)
         return TRUE;
 
+    /* Reset the pager state: number of printed rows/cols and aborted output flag */
+    KdbNumberOfRowsPrinted = KdbNumberOfColsPrinted = 0;
+    KdbOutputAborted = FALSE;
+
     for (i = 0; i < RTL_NUMBER_OF(KdbDebuggerCommands); i++)
     {
         if (!KdbDebuggerCommands[i].Name)
@@ -3245,18 +3250,20 @@ KdbpDoCommand(
 
         if (strcmp(KdbDebuggerCommands[i].Name, Argv[0]) == 0)
         {
-            return KdbDebuggerCommands[i].Fn(Argc, Argv);
+            Continue = KdbDebuggerCommands[i].Fn(Argc, Argv);
+            goto Done;
         }
     }
 
     /* Now invoke the registered callbacks */
     if (KdbpInvokeCliCallbacks(Command, Argc, Argv))
-    {
-        return TRUE;
-    }
+        goto Done;
 
-    KdbpPrint("Command '%s' is unknown.\n", OrigCommand);
-    return TRUE;
+    KdbPrintf("Command '%s' is unknown.\n", OrigCommand);
+
+Done:
+    KdbOutputAborted = FALSE;
+    return Continue;
 }
 
 /*!\brief KDB Main Loop.
@@ -3267,39 +3274,37 @@ VOID
 KdbpCliMainLoop(
     IN BOOLEAN EnteredOnSingleStep)
 {
-    BOOLEAN Continue;
-    SIZE_T CmdLen;
+    BOOLEAN Continue = TRUE;
     static CHAR Command[1024];
     static CHAR LastCommand[1024] = "";
 
     if (EnteredOnSingleStep)
     {
         if (!KdbSymPrintAddress((PVOID)KeGetContextPc(KdbCurrentTrapFrame), KdbCurrentTrapFrame))
-        {
-            KdbpPrint("<%p>", KeGetContextPc(KdbCurrentTrapFrame));
-        }
+            KdbPrintf("<%p>", KeGetContextPc(KdbCurrentTrapFrame));
 
-        KdbpPrint(": ");
+        KdbPuts(": ");
         if (KdbpDisassemble(KeGetContextPc(KdbCurrentTrapFrame), KdbUseIntelSyntax) < 0)
-        {
-            KdbpPrint("<INVALID>");
-        }
-        KdbpPrint("\n");
+            KdbPuts("<INVALID>");
+        KdbPuts("\n");
+    }
+    else
+    {
+        /* Preceding this message is one of the "Entered debugger..." banners */
+        // KdbPuts("\nEntered debugger\n");
+        KdbPuts("\nType \"help\" for a list of commands.\n");
     }
 
     /* Main loop */
-    do
+    while (Continue)
     {
-        /* Reset the number of rows/cols printed */
-        KdbNumberOfRowsPrinted = KdbNumberOfColsPrinted = 0;
-
         /*
          * Print the prompt and read a command.
          * Repeat the last one if the user pressed Enter.
          * This reduces the risk of RSI when single-stepping!
          */
         // TEMP HACK! Issue an empty string instead of duplicating "kdb:>"
-        CmdLen = KdbPrompt(/*KdbPromptStr.Buffer*/"", Command, sizeof(Command));
+        SIZE_T CmdLen = KdbPrompt(/*KdbPromptStr.Buffer*/"", Command, sizeof(Command));
         if (CmdLen == 0)
         {
             /* Nothing received but the user didn't press Enter, retry */
@@ -3320,15 +3325,9 @@ KdbpCliMainLoop(
             RtlStringCbCopyA(Command, sizeof(Command), LastCommand);
         }
 
-        /* Reset the number of rows/cols printed and output aborted state */
-        KdbNumberOfRowsPrinted = KdbNumberOfColsPrinted = 0;
-        KdbOutputAborted = FALSE;
-
-        /* Call the command */
+        /* Invoke the command */
         Continue = KdbpDoCommand(Command);
-        KdbOutputAborted = FALSE;
     }
-    while (Continue);
 }
 
 /*!\brief This function is called by KdbEnterDebuggerException...