1 files changed, 118 insertions, 0 deletions
diff --git a/xbmc/platform/posix/utils/SharedMemory.cpp b/xbmc/platform/posix/utils/SharedMemory.cpp
new file mode 100644
index 0000000..6c1318e
--- /dev/null
+++ b/xbmc/platform/posix/utils/SharedMemory.cpp
@@ -0,0 +1,118 @@
+/*
+ *  Copyright (C) 2017-2018 Team Kodi
+ *  This file is part of Kodi - https://kodi.tv
+ *
+ *  SPDX-License-Identifier: GPL-2.0-or-later
+ *  See LICENSES/README.md for more information.
+ */
+
+#include "SharedMemory.h"
+
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#if defined(HAVE_LINUX_MEMFD)
+#include <linux/memfd.h>
+#include <sys/syscall.h>
+#endif
+
+#include <cerrno>
+#include <cstdlib>
+#include <system_error>
+
+#include "utils/log.h"
+
+using namespace KODI::UTILS::POSIX;
+
+CSharedMemory::CSharedMemory(std::size_t size)
+: m_size{size}, m_fd{Open()}, m_mmap(nullptr, m_size, PROT_READ | PROT_WRITE, MAP_SHARED, m_fd, 0)
+{
+}
+
+CFileHandle CSharedMemory::Open()
+{
+  CFileHandle fd;
+  try
+  {
+    fd = OpenMemfd();
+  }
+  catch (std::system_error const& error)
+  {
+    if (error.code() == std::errc::function_not_supported)
+    {
+      CLog::Log(LOGDEBUG, "Kernel does not support memfd, falling back to plain shm");
+      fd = OpenShm();
+    }
+    else
+    {
+      throw;
+    }
+  }
+
+  if (ftruncate(fd, m_size) < 0)
+  {
+    throw std::system_error(errno, std::generic_category(), "ftruncate");
+  }
+
+  return fd;
+}
+
+CFileHandle CSharedMemory::OpenMemfd()
+{
+#if defined(SYS_memfd_create) && defined(HAVE_LINUX_MEMFD)
+  // This is specific to Linux >= 3.17, but preferred over shm_create if available
+  // because it is race-free
+  int fd = syscall(SYS_memfd_create, "kodi", MFD_CLOEXEC);
+  if (fd < 0)
+  {
+    throw std::system_error(errno, std::generic_category(), "memfd_create");
+  }
+
+  return CFileHandle(fd);
+#else
+  throw std::system_error(std::make_error_code(std::errc::function_not_supported), "memfd_create");
+#endif
+}
+
+CFileHandle CSharedMemory::OpenShm()
+{
+  char* xdgRuntimeDir = std::getenv("XDG_RUNTIME_DIR");
+  if (!xdgRuntimeDir)
+  {
+    throw std::runtime_error("XDG_RUNTIME_DIR environment variable must be set");
+  }
+
+  std::string tmpFilename(xdgRuntimeDir);
+  tmpFilename.append("/kodi-shared-XXXXXX");
+
+  int rawFd;
+#if defined(HAVE_MKOSTEMP)
+  // Opening the file with O_CLOEXEC is preferred since it avoids races where
+  // other threads might exec() before setting the CLOEXEC flag
+  rawFd = mkostemp(&tmpFilename[0], O_CLOEXEC);
+#else
+  rawFd = mkstemp(&tmpFilename[0]);
+#endif
+
+  if (rawFd < 0)
+  {
+    throw std::system_error(errno, std::generic_category(), "mkstemp");
+  }
+  CFileHandle fd(rawFd);
+
+  int flags = fcntl(fd, F_GETFD);
+  if (flags < 0)
+  {
+    throw std::system_error(errno, std::generic_category(), "fcntl F_GETFD");
+  }
+  // Set FD_CLOEXEC if unset
+  if (!(flags & FD_CLOEXEC) && fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
+  {
+    throw std::system_error(errno, std::generic_category(), "fcntl F_SETFD FD_CLOEXEC");
+  }
+
+  unlink(tmpFilename.c_str());
+
+  return fd;
+}
+\ No newline at end of file