Mojo: Implement MojoUnmapBuffer().

mojo/system/constants.h

 // Copyright 2013 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.
 
 #ifndef MOJO_SYSTEM_CONSTANTS_H_
 #define MOJO_SYSTEM_CONSTANTS_H_
 
 #include <stddef.h>
 
 namespace mojo {
 namespace system {
 
-// Maximum of open (Mojo) handles.
+// Maximum number of open (Mojo) handles.
 // TODO(vtl): This doesn't count "live" handles, some of which may live in
 // messages.
 const size_t kMaxHandleTableSize = 1000000;
 
+// Maximum number of active memory mappings.
+const size_t kMaxMappingTableSize = 1000000;
+
 const size_t kMaxWaitManyNumHandles = kMaxHandleTableSize;
 
 const size_t kMaxMessageNumBytes = 4 * 1024 * 1024;
 
 const size_t kMaxMessageNumHandles = 10000;
 
 // Maximum capacity of a data pipe, in bytes. This value must fit into a
 // |uint32_t|.
 // WARNING: If you bump it closer to 2^32, you must audit all the code to check
 // that we don't overflow (2^31 would definitely be risky; up to 2^30 is
 // probably okay).
 const size_t kMaxDataPipeCapacityBytes = 256 * 1024 * 1024;  // 256 MB.
 
 const size_t kDefaultDataPipeCapacityBytes = 1024 * 1024;  // 1 MB.
 
 // Alignment for the "start" of the data buffer used by data pipes. (The
 // alignment of elements will depend on this and the element size.)
 const size_t kDataPipeBufferAlignmentBytes = 16;
 
 // TODO(vtl): Set this hard limit appropriately (e.g., higher on 64-bit). (This
 // will also entail some auditing to make sure I'm not messing up my checks
 // anywhere.)
 const size_t kMaxSharedMemoryNumBytes = 1024 * 1024 * 1024;  // 1 GB.
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_CONSTANTS_H_