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Subject:	mmap bug
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From:	Kazuhiro Fujieda <fujieda AT jaist DOT ac DOT jp>
Date:	05 Mar 1999 17:03:44 +0900
Message-ID:	<ug17kgy73.fsf@parvati.will.or.jp>
Lines:	53
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mmap() with the MAP_PRIVATE mapping type and the PROT_WRITE
protection mode, always fails in MapViewOfFile() with the error
of INVALID_PARAMETER (on Win95) or ACCESS_DENIED (on WinNT).

In this case, mmap() passes FILE_MAP_WRITE | FILE_MAP_COPY to
MapViewOfFile() as its access mode. But according to the
Platform SDK Documentation, it should be either FILE_MAP_WRITE
or FILE_MAP_COPY.

If its access mode is FILE_MAP_READ | FILE_MAP_COPY,
MapViewOfFile() works well against the document. I guess it
picks FILE_MAP_READ only.  The following patch is based on this
guess.

--- mmap.cc-	Wed Feb 03 13:55:21 1999
+++ mmap.cc	Fri Feb 26 15:54:12 1999
@@ -181,16 +181,24 @@ mmap (caddr_t addr, size_t len, int prot
 	}
     }
 
-  DWORD access = (prot & PROT_WRITE) ? FILE_MAP_WRITE : FILE_MAP_READ;
-  access |= (flags & MAP_PRIVATE) ? FILE_MAP_COPY : 0;
-  DWORD protect;
+  DWORD protect, access;
 
-  if (access & FILE_MAP_COPY)
-    protect = PAGE_WRITECOPY;
-  else if (access & FILE_MAP_WRITE)
-    protect = PAGE_READWRITE;
+
+  if (!(prot & PROT_WRITE))
+    {
+      protect = PAGE_READONLY;
+      access = FILE_MAP_READ;
+    }
+  else if (flags & MAP_PRIVATE)
+    {
+      protect = PAGE_WRITECOPY;
+      access = FILE_MAP_COPY;
+    }
   else
-    protect = PAGE_READONLY;
+    {
+      protect = PAGE_READWRITE;
+      access = FILE_MAP_WRITE;
+    }
 
   HANDLE hFile;
 
____
  | AIST      Kazuhiro Fujieda <fujieda AT jaist DOT ac DOT jp>
  | HOKURIKU  School of Information Science
o_/ 1990      Japan Advanced Institute of Science and Technology

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