Use ftruncate() instead of fwrite() to extend files....

base/shared_memory_posix.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/shared_memory.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ skipping 176 matching lines @@
     }
 
     fp = file_util::OpenFile(mem_filename, mode.c_str());
   }
 
   if (fp == NULL)
     return false;
   file_closer.reset(fp);  // close when we go out of scope
 
   // Make sure the (new) file is the right size.
-  // According to the man page, "Use of truncate() to extend a file is
-  // not portable."
   if (size && (posix_flags & (O_RDWR | O_CREAT))) {
     // Get current size.
     size_t current_size = 0;

[Mark Mentovai, 2009/08/26 01:22:51]

While you're here, move the declaration down to where it's actually used.

[pink (ping after 24hrs), 2009/08/26 15:16:57]

Done.

     struct stat stat;
     if (fstat(fileno(fp), &stat) != 0)
       return false;
     current_size = stat.st_size;
-    // Possibly grow.
-    if (current_size < size) {
-      if (fseeko(fp, current_size, SEEK_SET) != 0)
+    if (current_size != size) {
+      if (ftruncate(fileno(fp), size) != 0)
         return false;
-      size_t writesize = size - current_size;
-      scoped_array<char> buf(new char[writesize]);
-      memset(buf.get(), 0, writesize);
-      if (fwrite(buf.get(), 1, writesize, fp) != writesize) {
-          return false;
-      }
-      if (fflush(fp) != 0)
+      if (fseeko(fp, size, SEEK_SET) != 0)
         return false;
-    } else if (current_size > size) {
-      // possibly shrink.
-      if ((ftruncate(fileno(fp), size) != 0) ||
-          (fflush(fp) != 0)) {
-        return false;
-      }
     }
   }
 
   mapped_file_ = dup(fileno(fp));
   if (mapped_file_ == -1) {
     if (errno == EMFILE) {
       LOG(WARNING) << "Shared memory creation failed; out of file descriptors";
       return false;
     } else {
       NOTREACHED() << "Call to dup failed, errno=" << errno;
@@ skipping 82 matching lines @@
 
 void SharedMemory::Unlock() {
   LockOrUnlockCommon(F_ULOCK);
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
   return FileDescriptor(mapped_file_, false);
 }
 
 }  // namespace base