text: // Copyright (c) 2012 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>
  #include <unistd.h>
  
  #include "base/file_util.h"
  #include "base/lazy_instance.h"
  #include "base/logging.h"
  #include "base/threading/platform_thread.h"
  #include "base/safe_strerror_posix.h"
  #include "base/synchronization/lock.h"
  #include "base/threading/thread_restrictions.h"
  #include "base/utf_string_conversions.h"
  
  #if defined(OS_MACOSX)
  #include "base/mac/foundation_util.h"
  #endif  // OS_MACOSX
  
  #if defined(OS_ANDROID)
  #include "base/os_compat_android.h"
  #include "third_party/ashmem/ashmem.h"
  #endif
  
  namespace base {
  
  namespace {
  
  // Paranoia. Semaphores and shared memory segments should live in different
  // namespaces, but who knows what's out there.
  const char kSemaphoreSuffix[] = "-sem";
  
  LazyInstance<Lock>::Leaky g_thread_lock_ = LAZY_INSTANCE_INITIALIZER;
  
  }
  
  SharedMemory::SharedMemory()
      : mapped_file_(-1),
        mapped_size_(0),
        inode_(0),
        memory_(NULL),
        read_only_(false),
        created_size_(0) {
  }
  
  SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only)
      : mapped_file_(handle.fd),
        mapped_size_(0),
        inode_(0),
        memory_(NULL),
        read_only_(read_only),
        created_size_(0) {
    struct stat st;
    if (fstat(handle.fd, &st) == 0) {
      // If fstat fails, then the file descriptor is invalid and we'll learn this
      // fact when Map() fails.
      inode_ = st.st_ino;
    }
  }
  
  SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only,
                             ProcessHandle process)
      : mapped_file_(handle.fd),
        mapped_size_(0),
        inode_(0),
        memory_(NULL),
        read_only_(read_only),
        created_size_(0) {
    // We don't handle this case yet (note the ignored parameter); let's die if
    // someone comes calling.
    NOTREACHED();
  }
  
  SharedMemory::~SharedMemory() {
    Close();
  }
  
  // static
  bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
    return handle.fd >= 0;
  }
  
  // static
  SharedMemoryHandle SharedMemory::NULLHandle() {
    return SharedMemoryHandle();
  }
  
  // static
  void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
    DCHECK_GE(handle.fd, 0);
    if (HANDLE_EINTR(close(handle.fd)) < 0)
      DPLOG(ERROR) << "close";
  }
  
  bool SharedMemory::CreateAndMapAnonymous(uint32 size) {
    return CreateAnonymous(size) && Map(size);
  }
  
  #if !defined(OS_ANDROID)
  // Chromium mostly only uses the unique/private shmem as specified by
  // "name == L"". The exception is in the StatsTable.
  // TODO(jrg): there is no way to "clean up" all unused named shmem if
  // we restart from a crash.  (That isn't a new problem, but it is a problem.)
  // In case we want to delete it later, it may be useful to save the value
  // of mem_filename after FilePathForMemoryName().
  bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
    DCHECK_EQ(-1, mapped_file_);
    if (options.size == 0) return false;
  
    // This function theoretically can block on the disk, but realistically
    // the temporary files we create will just go into the buffer cache
    // and be deleted before they ever make it out to disk.
    base::ThreadRestrictions::ScopedAllowIO allow_io;
  
    FILE *fp;
    bool fix_size = true;
  
    FilePath path;
    if (options.name == NULL || options.name->empty()) {
      // It doesn't make sense to have a open-existing private piece of shmem
      DCHECK(!options.open_existing);
      // Q: Why not use the shm_open() etc. APIs?
      // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU
      fp = file_util::CreateAndOpenTemporaryShmemFile(&path, options.executable);
  
      // Deleting the file prevents anyone else from mapping it in
      // (making it private), and prevents the need for cleanup (once
      // the last fd is closed, it is truly freed).
      if (fp)
        file_util::Delete(path, false);
  
    } else {
      if (!FilePathForMemoryName(*options.name, &path))
        return false;
  
      fp = file_util::OpenFile(path, "w+x");
      if (fp == NULL && options.open_existing) {
        // "w+" will truncate if it already exists.
        fp = file_util::OpenFile(path, "a+");
        fix_size = false;
      }
    }
    if (fp && fix_size) {
      // Get current size.
      struct stat stat;
      if (fstat(fileno(fp), &stat) != 0) {
        file_util::CloseFile(fp);
        return false;
      }
      const uint32 current_size = stat.st_size;
      if (current_size != options.size) {
        if (HANDLE_EINTR(ftruncate(fileno(fp), options.size)) != 0) {
          file_util::CloseFile(fp);
          return false;
        }
        if (fseeko(fp, options.size, SEEK_SET) != 0) {
          file_util::CloseFile(fp);
          return false;
        }
      }
      created_size_ = options.size;
    }
    if (fp == NULL) {
  #if !defined(OS_MACOSX)
      PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
      FilePath dir = path.DirName();
      if (access(dir.value().c_str(), W_OK | X_OK) < 0) {
        PLOG(ERROR) << "Unable to access(W_OK|X_OK) " << dir.value();
        if (dir.value() == "/dev/shm") {
          LOG(FATAL) << "This is frequently caused by incorrect permissions on "
                     << "/dev/shm.  Try 'sudo chmod 1777 /dev/shm' to fix.";
        }
      }
  #else
      PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
  #endif
      return false;
    }
  
    return PrepareMapFile(fp);
  }
  
  // Our current implementation of shmem is with mmap()ing of files.
  // These files need to be deleted explicitly.
  // In practice this call is only needed for unit tests.
  bool SharedMemory::Delete(const std::string& name) {
    FilePath path;
    if (!FilePathForMemoryName(name, &path))
      return false;
  
    if (file_util::PathExists(path)) {
      return file_util::Delete(path, false);
    }
  
    // Doesn't exist, so success.
    return true;
  }
  
  bool SharedMemory::Open(const std::string& name, bool read_only) {
    FilePath path;
    if (!FilePathForMemoryName(name, &path))
      return false;
  
    read_only_ = read_only;
  
    const char *mode = read_only ? "r" : "r+";
    FILE *fp = file_util::OpenFile(path, mode);
    return PrepareMapFile(fp);
  }
  
  #endif  // !defined(OS_ANDROID)
  
  bool SharedMemory::Map(uint32 bytes) {
    if (mapped_file_ == -1)
      return false;
  
  #if defined(OS_ANDROID)
    if (bytes == 0) {
      int ashmem_bytes = ashmem_get_size_region(mapped_file_);
      if (ashmem_bytes < 0)
        return false;
  
      DCHECK_GE(static_cast<uint32>(ashmem_bytes), bytes);
      // The caller wants to determine the map region size from ashmem.
      bytes = ashmem_bytes;
      // TODO(port): we set the created size here so that it is available in
      // transport_dib_android.cc. We should use ashmem_get_size_region()
      // in transport_dib_android.cc.
      created_size_ = bytes;
    }
  #endif
  
    memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
                   MAP_SHARED, mapped_file_, 0);
  
    bool mmap_succeeded = memory_ != (void*)-1 && memory_ != NULL;
    if (mmap_succeeded) {
      mapped_size_ = bytes;
      DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
          (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
    } else {
      memory_ = NULL;
    }
  
    return mmap_succeeded;
  }
  
  bool SharedMemory::Unmap() {
    if (memory_ == NULL)
      return false;
  
    munmap(memory_, mapped_size_);
    memory_ = NULL;
    mapped_size_ = 0;
    return true;
  }
  
  SharedMemoryHandle SharedMemory::handle() const {
    return FileDescriptor(mapped_file_, false);
  }
  
  void SharedMemory::Close() {
    Unmap();
  
    if (mapped_file_ > 0) {
      if (HANDLE_EINTR(close(mapped_file_)) < 0)
        PLOG(ERROR) << "close";
      mapped_file_ = -1;
    }
  }
  
  void SharedMemory::Lock() {
    g_thread_lock_.Get().Acquire();
    LockOrUnlockCommon(F_LOCK);
  }
  
  void SharedMemory::Unlock() {
    LockOrUnlockCommon(F_ULOCK);
    g_thread_lock_.Get().Release();
  }
  
  #if !defined(OS_ANDROID)
  bool SharedMemory::PrepareMapFile(FILE *fp) {
    DCHECK_EQ(-1, mapped_file_);
    if (fp == NULL) return false;
  
    // This function theoretically can block on the disk, but realistically
    // the temporary files we create will just go into the buffer cache
    // and be deleted before they ever make it out to disk.
    base::ThreadRestrictions::ScopedAllowIO allow_io;
  
    file_util::ScopedFILE file_closer(fp);
  
    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;
      }
    }
  
    struct stat st;
    if (fstat(mapped_file_, &st))
      NOTREACHED();
    inode_ = st.st_ino;
  
    return true;
  }
  #endif
  
  // For the given shmem named |mem_name|, return a filename to mmap()
  // (and possibly create).  Modifies |filename|.  Return false on
  // error, or true of we are happy.
  bool SharedMemory::FilePathForMemoryName(const std::string& mem_name,
                                           FilePath* path) {
    // mem_name will be used for a filename; make sure it doesn't
    // contain anything which will confuse us.
    DCHECK_EQ(std::string::npos, mem_name.find('/'));
    DCHECK_EQ(std::string::npos, mem_name.find('\0'));
  
    FilePath temp_dir;
    if (!file_util::GetShmemTempDir(&temp_dir, false))
      return false;
  
  #if !defined(OS_MACOSX)
  #if defined(GOOGLE_CHROME_BUILD)
    std::string name_base = std::string("com.google.Chrome");
  #else
    std::string name_base = std::string("org.chromium.Chromium");
  #endif
  #else  // OS_MACOSX
    std::string name_base = std::string(base::mac::BaseBundleID());
  #endif  // OS_MACOSX
    *path = temp_dir.AppendASCII(name_base + ".shmem." + mem_name);
    return true;
  }
  
  void SharedMemory::LockOrUnlockCommon(int function) {
    DCHECK_GE(mapped_file_, 0);
    while (lockf(mapped_file_, function, 0) < 0) {
      if (errno == EINTR) {
        continue;
      } else if (errno == ENOLCK) {
        // temporary kernel resource exaustion
        base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(500));
        continue;
      } else {
        NOTREACHED() << "lockf() failed."
                     << " function:" << function
                     << " fd:" << mapped_file_
                     << " errno:" << errno
                     << " msg:" << safe_strerror(errno);
      }
    }
  }
  
  bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                          SharedMemoryHandle *new_handle,
                                          bool close_self) {
    const int new_fd = dup(mapped_file_);
    DCHECK_GE(new_fd, 0);
    new_handle->fd = new_fd;
    new_handle->auto_close = true;
  
    if (close_self)
      Close();
  
    return true;
  }
  
  }  // namespace base
  