Bug: OS::MemoryMappedFile::open() should not truncate a pre-existing file.

src/platform-linux.cc

Index: src/platform-linux.cc
===================================================================
--- src/platform-linux.cc	(revision 6858)
+++ src/platform-linux.cc	(working copy)
@@ -327,7 +327,7 @@
 
 
 OS::MemoryMappedFile* OS::MemoryMappedFile::open(const char* name) {
-  FILE* file = fopen(name, "w+");
+  FILE* file = fopen(name, "a+");

[mnaganov (inactive), 2011/02/21 10:37:56]

I don't think "a+" is the right flag. If you plan to read and write to the file
from the beginning, and avoid truncating it, then you should use "r+". This
concern has arisen to me because in 'mmap' you pass 0 as the offset inside the
file, which contradicts with the "a" flag semantics that means appending data to
a file. Thus, using both "a" and "0" offset seems like a contradiction. Also,
you don't pass 'FILE_APPEND_DATA' to the Win32 function, so I'm concluding you
really don't want to append to the file.

   if (file == NULL) return NULL;
 
   fseek(file, 0, SEEK_END);