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/*
* 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;
}
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