From d99cfc38c180000416bab4af299da1f13222d3fc Mon Sep 17 00:00:00 2001
From: Bart Oldeman <bart@dosemu.org>
Date: Tue, 15 May 2007 17:50:22 +0000
Subject: [PATCH] Add Tom Ehlert's freeing of near f_node's work-around for
 problems with INT24 handling.

git-svn-id: https://svn.code.sf.net/p/freedos/svn/kernel/trunk@1317 6ac86273-5f31-0410-b378-82cca8765d1b
---
 kernel/inthndlr.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/kernel/inthndlr.c b/kernel/inthndlr.c
index 82092a6..7d3ca2c 100644
--- a/kernel/inthndlr.c
+++ b/kernel/inthndlr.c
@@ -425,7 +425,29 @@ dispatch:
   }
   /* Clear carry by default for these functions */
 
-
+  /* We force clear the near fnodes,
+     On a normal int21h entry these are unused, so should already
+     be clear, thus this code is effectively redundant.
+     However when re-entering int21h, such as a device driver
+     (e.g. shsufdrv), the fnodes may contain the values of the
+     in progress call; as long as the driver/tsr causing the
+     reentrancey saves and restores the SDA across the call then
+     any changes we do (ie clearing these) should go unnoticed
+     and if the cause of the reentrancy does not save/restore the
+     SDA then the caller should expected the unexpected.
+     Failure to do this will at a minimal result in the extra
+     output indicating fnodes not 0 (and possibly clearing at end
+     of call) when the re-entered int21h call completes, but could
+     result in the re-entered call to fail with no free near fnodes
+     if both are already in use by the original int21h call (?bug 1879?).
+     See also PATCH TE 5 jul 04 explanation at end 
+   */
+  if (/*ErrorMode && */lr.AH > 0x0c && lr.AH != 0x30 && lr.AH != 0x59)
+  {
+    /*if (ErrorMode)*/ ErrorMode = 0;
+    fnode[0].f_count = 0;    /* don't panic - THEY ARE unused !! */
+    fnode[1].f_count = 0;
+  }
   /* Check for Ctrl-Break */
   if (break_ena || (lr.AH >= 1 && lr.AH <= 5) || (lr.AH >= 8 && lr.AH <= 0x0b))
     check_handle_break(&syscon);
@@ -1545,6 +1567,31 @@ exit_dispatch:
   r->ES = lr.ES;
 real_exit:;
 
+  /* PATCH !!       TE 5 JUL 04
+     what happened:
+     Application does FindFirst("I:\*.*");
+     this fails, and causes Int24
+     this sets ErrorMode, and calls Int24
+     Application decides NOT to return to DOS,
+     but instead pop the stack and return to itself
+     (this is legal; see RBIL/INT 24 description
+
+     a) now the alloc()'ed fnode[0] never gets free()'ed
+     b) errormode NEVER gets set back to 0 unyil exit()
+
+     I have NO idea how real DOS handles this;
+     the appended patch cures the worst symptoms
+  */
+  if (fnode[0].f_count != 0 ||
+      fnode[1].f_count != 0 )
+  {
+    if (ErrorMode == 0)
+      put_string("near_fnodes not 0"); /* panic ?? */
+    fnode[0].f_count = 0;    /* don't panic - THEY ARE unused !! */
+    fnode[1].f_count = 0;
+  }
+  /* PATCH !! END    TE 5 JUL 04 */
+
 #ifdef DEBUG
   if (bDumpRegs)
   {