Pass StatsTable shared memory via global descriptors on Posix rather than using named shared memory.

components/nacl/common/nacl_helper_linux.h

Index: components/nacl/common/nacl_helper_linux.h
diff --git a/components/nacl/common/nacl_helper_linux.h b/components/nacl/common/nacl_helper_linux.h
index a9324b3fa1d786a2cd705bcad2d33cd36b9747ca..9b3b0659b39d55fd68deabd179f7ee541831df5f 100644
--- a/components/nacl/common/nacl_helper_linux.h
+++ b/components/nacl/common/nacl_helper_linux.h
@@ -25,23 +25,25 @@ enum NaClZygoteIPCCommand {
 // http://code.google.com/p/chromium/wiki/LinuxZygote
 
 // For communications between NaCl loader and zygote.
-#define kNaClZygoteDescriptor 3
+#define kNaClZygoteDescriptor 4
 // For communications between the NaCl loader process and
 // the SUID sandbox.
-#define kNaClSandboxDescriptor 5
+#define kNaClSandboxDescriptor 6
 // NOTE: kNaClSandboxDescriptor must match
-// content/browser/zygote_main_linux.cc
-// kMagicSandboxIPCDescriptor.
+// content/public/common/content_descriptors.h
+// kSandboxIPCChannel + base::GlobalDescriptors::kBaseDescriptor
 
 // A fork request from the Zygote to the helper includes an array
-// of three file descriptors. These constants are used as indicies
+// of three or four file descriptors. These constants are used as indicies
 // into the array.
 // Used to pass in the descriptor for talking to the Browser
 #define kNaClBrowserFDIndex 0
 // The next two are used in the protocol for discovering the
 // child processes real PID from within the SUID sandbox. See
 // http://code.google.com/p/chromium/wiki/LinuxZygote
-#define kNaClDummyFDIndex 1
-#define kNaClParentFDIndex 2
+// These indices depend on the size of the array, as kStatsTableSharedMemFd
+// could be inserted between kNaClBrowserFDIndex and kNaClDummyFDIndex.
+#define kNaClDummyFDIndex(fd_array_size) (fd_array_size == 3 ? 1 : 2)

[Mark Seaborn, 2013/09/12 00:00:28]

This should be an inline function rather than a macro -- functions are safer.

Also it should be renamed to remove the "k" prefix because it's not a constant
any more.

(But this assumes we want to plumb StatsTable through to NaCl processes -- see
other comment.)

[rmcilroy, 2013/09/12 17:04:56]

Done.

+#define kNaClParentFDIndex(fd_array_size) (fd_array_size == 3 ? 2 : 3)
 
 #endif  // COMPONENTS_NACL_COMMON_NACL_HELPER_LINUX_H_