--- mf_tempdir.orig.c	Wed Jul 19 17:10:42 2006
+++ mf_tempdir.c	Sat Nov 18 03:03:34 2006
@@ -16,6 +16,9 @@
 
 #include "mysys_priv.h"
 #include <m_string.h>
+#if defined( __WIN__) || defined(OS2) || defined(__NETWARE__)
+#include <sys/stat.h>      /* needed for tmp dir writability check, which is currently done only under DOSish OS's */
+#endif
 
 #if defined( __WIN__) || defined(OS2) || defined(__NETWARE__)
 #define DELIM ';'
@@ -25,36 +28,96 @@
 
 my_bool init_tmpdir(MY_TMPDIR *tmpdir, const char *pathlist)
 {
+  /* Get information into which directories temporary files should be placed:
+     If pathlist is specified: use this information (stage 0).
+     Else: Try, in turn, environment variables TMPDIR, TEMPDIR, TMP, TEMP (Windows; others only use TMPDIR).
+     (Call these attempts stage 1 through stage 4.)
+     Assume that this is a list of directories separated by ';' (Windows) or ':' (others).
+     For each such directory, check whether it exists and is writable. If yes, add it to a list
+     of tmp directories; otherwise, ignore this entry.
+     As soon as one of the stages yields one or more tmp directries, return without checking subsequent stages.
+     If none is successful, try '\' as a last resort (stage 5). This will be returned without writability check.
+     Gisbert W. Selke, 2006-11-18, for free use within MySQL.
+   */
   char *end, *copy;
   char buff[FN_REFLEN];
   DYNAMIC_ARRAY t_arr;
+#if defined(__WIN__) || defined(OS2) || defined(__NETWARE__)
+  struct _stat stat_buffer;  /* writability check: currently done only under DOSish OS's, should be used generally. */
+#endif
+  uint tmpnam_trycount;
+  my_bool tmpnam_lasttry=FALSE;
   pthread_mutex_init(&tmpdir->mutex, MY_MUTEX_INIT_FAST);
   if (my_init_dynamic_array(&t_arr, sizeof(char*), 1, 5))
     return TRUE;
-  if (!pathlist || !pathlist[0])
+  tmpnam_trycount=0;
+  tmpnam_lasttry=FALSE;
+  while (!t_arr.elements)
   {
-    /* Get default temporary directory */
-    pathlist=getenv("TMPDIR");	/* Use this if possible */
-#if defined( __WIN__) || defined(OS2) || defined(__NETWARE__)
-    if (!pathlist)
-      pathlist=getenv("TEMP");
-    if (!pathlist)
-      pathlist=getenv("TMP");
+    switch(tmpnam_trycount)
+    {
+      case 0  :                             break; /* Try initial assignment */
+      case 1  : pathlist=getenv("TMPDIR");  break; /* Try this next if possible */
+#if defined(__WIN__) || defined(OS2) || defined(__NETWARE__)
+      case 2  : pathlist=getenv("TEMPDIR"); break; /* Try these only under DOSish OS's */
+      case 3  : pathlist=getenv("TMP");     break;
+      case 4  : pathlist=getenv("TEMP");    break;
 #endif
-    if (!pathlist || !pathlist[0])
-      pathlist=(char*) P_tmpdir;
-  }
-  do
-  {
-    end=strcend(pathlist, DELIM);
-    convert_dirname(buff, pathlist, end);
-    if (!(copy=my_strdup(buff, MYF(MY_WME))))
-      return TRUE;
-    if (insert_dynamic(&t_arr, (gptr)&copy))
-      return TRUE;
-    pathlist=end+1;
+      default : pathlist=(char*) P_tmpdir;  tmpnam_lasttry=TRUE; break; /* Last resort */
+    }
+    if ((pathlist && pathlist[0]) || tmpnam_lasttry)
+    {
+      do
+      {
+        end=strcend(pathlist, DELIM);
+        convert_dirname(buff, pathlist, end);
+#if defined(__WIN__) || defined(OS2) || defined(__NETWARE__)
+        /* The putative dirname now has a directory delimiter at its end, which is not liked by _stat.
+           So we remove it temporarily before we check whether directory exists and is writable.
+         */
+        copy = (char *)memchr(buff, '\0', FN_REFLEN) - 1;
+        if ((copy-buff > 0) && (*copy == FN_LIBCHAR) && ((copy-buff == 0) || (*(copy-1) != FN_DEVCHAR)))
+        {
+          *copy = '\0';
+        }
+        else
+        {
+          copy = NULL;
+        }
+        /* writability check: currently done only under DOSish OS's, should be used generally:
+           Use only writable directories, if possible, but make sure we're never without at least one.
+         */
+        if (tmpnam_lasttry ||
+            ((_stat(buff, &stat_buffer) >= 0) &&
+             (stat_buffer.st_mode & _S_IFDIR) &&
+             (stat_buffer.st_mode & _S_IWRITE)
+            )
+           )
+        {
+          /* Restore final dir delimiter if we removed it earlier on: */
+          if (copy) *copy = FN_LIBCHAR;
+          if (!(copy=my_strdup(buff, MYF(MY_WME))))
+            return TRUE;
+          if (insert_dynamic(&t_arr, (gptr)&copy))
+            return TRUE;
+        }
+#else
+        /* For other OS's, we currently don't check accessibility and writability, but only because
+           I (gws) cannot test it. So, the whole ifdef monkeying should really be removed so that
+           all OS's get the same treatment.
+         */
+        if (!(copy=my_strdup(buff, MYF(MY_WME))))
+          return TRUE;
+        if (insert_dynamic(&t_arr, (gptr)&copy))
+          return TRUE;
+#endif
+        pathlist=end+1;
+      }
+      while (*end);
+    }
+    tmpnam_trycount++;
   }
-  while (*end);
+
   freeze_size(&t_arr);
   tmpdir->list=(char **)t_arr.buffer;
   tmpdir->max=t_arr.elements-1;