path: root/xpcom/glue/FileUtils.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include <errno.h>
#include <stdio.h>

#include "nscore.h"
#include "nsStringGlue.h"
#include "private/pprio.h"
#include "mozilla/Assertions.h"
#include "mozilla/FileUtils.h"

#if defined(XP_UNIX)
#include <fcntl.h>
#include <unistd.h>
#if defined(LINUX)
#include <elf.h>
#endif
#include <sys/types.h>
#include <sys/stat.h>
#elif defined(XP_WIN)
#include <windows.h>
#endif

// Functions that are not to be used in standalone glue must be implemented
// within this #if block
#if !defined(XPCOM_GLUE)

bool
mozilla::fallocate(PRFileDesc* aFD, int64_t aLength)
{
#if defined(HAVE_POSIX_FALLOCATE)
  return posix_fallocate(PR_FileDesc2NativeHandle(aFD), 0, aLength) == 0;
#elif defined(XP_WIN)
  int64_t oldpos = PR_Seek64(aFD, 0, PR_SEEK_CUR);
  if (oldpos == -1) {
    return false;
  }

  if (PR_Seek64(aFD, aLength, PR_SEEK_SET) != aLength) {
    return false;
  }

  bool retval = (0 != SetEndOfFile((HANDLE)PR_FileDesc2NativeHandle(aFD)));

  PR_Seek64(aFD, oldpos, PR_SEEK_SET);
  return retval;
#elif defined(XP_UNIX)
  // The following is copied from fcntlSizeHint in sqlite
  /* If the OS does not have posix_fallocate(), fake it. First use
  ** ftruncate() to set the file size, then write a single byte to
  ** the last byte in each block within the extended region. This
  ** is the same technique used by glibc to implement posix_fallocate()
  ** on systems that do not have a real fallocate() system call.
  */
  int64_t oldpos = PR_Seek64(aFD, 0, PR_SEEK_CUR);
  if (oldpos == -1) {
    return false;
  }

  struct stat buf;
  int fd = PR_FileDesc2NativeHandle(aFD);
  if (fstat(fd, &buf)) {
    return false;
  }

  if (buf.st_size >= aLength) {
    return false;
  }

  const int nBlk = buf.st_blksize;

  if (!nBlk) {
    return false;
  }

  if (ftruncate(fd, aLength)) {
    return false;
  }

  int nWrite; // Return value from write()
  int64_t iWrite = ((buf.st_size + 2 * nBlk - 1) / nBlk) * nBlk - 1; // Next offset to write to
  while (iWrite < aLength) {
    nWrite = 0;
    if (PR_Seek64(aFD, iWrite, PR_SEEK_SET) == iWrite) {
      nWrite = PR_Write(aFD, "", 1);
    }
    if (nWrite != 1) {
      break;
    }
    iWrite += nBlk;
  }

  PR_Seek64(aFD, oldpos, PR_SEEK_SET);
  return nWrite == 1;
#endif
  return false;
}

#ifdef ReadSysFile_PRESENT

bool
mozilla::ReadSysFile(
  const char* aFilename,
  char* aBuf,
  size_t aBufSize)
{
  int fd = MOZ_TEMP_FAILURE_RETRY(open(aFilename, O_RDONLY));
  if (fd < 0) {
    return false;
  }
  ScopedClose autoClose(fd);
  if (aBufSize == 0) {
    return true;
  }
  ssize_t bytesRead;
  size_t offset = 0;
  do {
    bytesRead = MOZ_TEMP_FAILURE_RETRY(read(fd, aBuf + offset,
                                            aBufSize - offset));
    if (bytesRead == -1) {
      return false;
    }
    offset += bytesRead;
  } while (bytesRead > 0 && offset < aBufSize);
  MOZ_ASSERT(offset <= aBufSize);
  if (offset > 0 && aBuf[offset - 1] == '\n') {
    offset--;
  }
  if (offset == aBufSize) {
    MOZ_ASSERT(offset > 0);
    offset--;
  }
  aBuf[offset] = '\0';
  return true;
}

bool
mozilla::ReadSysFile(
  const char* aFilename,
  int* aVal)
{
  char valBuf[32];
  if (!ReadSysFile(aFilename, valBuf, sizeof(valBuf))) {
    return false;
  }
  return sscanf(valBuf, "%d", aVal) == 1;
}

bool
mozilla::ReadSysFile(
  const char* aFilename,
  bool* aVal)
{
  int v;
  if (!ReadSysFile(aFilename, &v)) {
    return false;
  }
  *aVal = (v != 0);
  return true;
}

#endif /* ReadSysFile_PRESENT */

#ifdef WriteSysFile_PRESENT

bool
mozilla::WriteSysFile(
  const char* aFilename,
  const char* aBuf)
{
  size_t aBufSize = strlen(aBuf);
  int fd = MOZ_TEMP_FAILURE_RETRY(open(aFilename, O_WRONLY));
  if (fd < 0) {
    return false;
  }
  ScopedClose autoClose(fd);
  ssize_t bytesWritten;
  size_t offset = 0;
  do {
    bytesWritten = MOZ_TEMP_FAILURE_RETRY(write(fd, aBuf + offset,
                                                aBufSize - offset));
    if (bytesWritten == -1) {
      return false;
    }
    offset += bytesWritten;
  } while (bytesWritten > 0 && offset < aBufSize);
  MOZ_ASSERT(offset == aBufSize);
  return true;
}

#endif /* WriteSysFile_PRESENT */

void
mozilla::ReadAheadLib(nsIFile* aFile)
{
#if defined(XP_WIN)
  nsAutoString path;
  if (!aFile || NS_FAILED(aFile->GetPath(path))) {
    return;
  }
  ReadAheadLib(path.get());
#elif defined(LINUX)
  nsAutoCString nativePath;
  if (!aFile || NS_FAILED(aFile->GetNativePath(nativePath))) {
    return;
  }
  ReadAheadLib(nativePath.get());
#endif
}

void
mozilla::ReadAheadFile(nsIFile* aFile, const size_t aOffset,
                       const size_t aCount, mozilla::filedesc_t* aOutFd)
{
#if defined(XP_WIN)
  nsAutoString path;
  if (!aFile || NS_FAILED(aFile->GetPath(path))) {
    return;
  }
  ReadAheadFile(path.get(), aOffset, aCount, aOutFd);
#elif defined(LINUX)
  nsAutoCString nativePath;
  if (!aFile || NS_FAILED(aFile->GetNativePath(nativePath))) {
    return;
  }
  ReadAheadFile(nativePath.get(), aOffset, aCount, aOutFd);
#endif
}

#endif // !defined(XPCOM_GLUE)

#if defined(LINUX)

static const unsigned int bufsize = 4096;

#ifdef __LP64__
typedef Elf64_Ehdr Elf_Ehdr;
typedef Elf64_Phdr Elf_Phdr;
static const unsigned char ELFCLASS = ELFCLASS64;
typedef Elf64_Off Elf_Off;
#else
typedef Elf32_Ehdr Elf_Ehdr;
typedef Elf32_Phdr Elf_Phdr;
static const unsigned char ELFCLASS = ELFCLASS32;
typedef Elf32_Off Elf_Off;
#endif

#endif

void
mozilla::ReadAhead(mozilla::filedesc_t aFd, const size_t aOffset,
                   const size_t aCount)
{
#if defined(XP_WIN)

  LARGE_INTEGER fpOriginal;
  LARGE_INTEGER fpOffset;
#if defined(HAVE_LONG_LONG)
  fpOffset.QuadPart = 0;
#else
  fpOffset.u.LowPart = 0;
  fpOffset.u.HighPart = 0;
#endif

  // Get the current file pointer so that we can restore it. This isn't
  // really necessary other than to provide the same semantics regarding the
  // file pointer that other platforms do
  if (!SetFilePointerEx(aFd, fpOffset, &fpOriginal, FILE_CURRENT)) {
    return;
  }

  if (aOffset) {
#if defined(HAVE_LONG_LONG)
    fpOffset.QuadPart = static_cast<LONGLONG>(aOffset);
#else
    fpOffset.u.LowPart = aOffset;
    fpOffset.u.HighPart = 0;
#endif

    if (!SetFilePointerEx(aFd, fpOffset, nullptr, FILE_BEGIN)) {
      return;
    }
  }

  char buf[64 * 1024];
  size_t totalBytesRead = 0;
  DWORD dwBytesRead;
  // Do dummy reads to trigger kernel-side readhead via FILE_FLAG_SEQUENTIAL_SCAN.
  // Abort when underfilling because during testing the buffers are read fully
  // A buffer that's not keeping up would imply that readahead isn't working right
  while (totalBytesRead < aCount &&
         ReadFile(aFd, buf, sizeof(buf), &dwBytesRead, nullptr) &&
         dwBytesRead == sizeof(buf)) {
    totalBytesRead += dwBytesRead;
  }

  // Restore the file pointer
  SetFilePointerEx(aFd, fpOriginal, nullptr, FILE_BEGIN);

#elif defined(LINUX)

  readahead(aFd, aOffset, aCount);

#endif
}

void
mozilla::ReadAheadLib(mozilla::pathstr_t aFilePath)
{
  if (!aFilePath) {
    return;
  }
#if defined(XP_WIN)
  ReadAheadFile(aFilePath);
#elif defined(LINUX)
  int fd = open(aFilePath, O_RDONLY);
  if (fd < 0) {
    return;
  }

  union
  {
    char buf[bufsize];
    Elf_Ehdr ehdr;
  } elf;
  // Read ELF header (ehdr) and program header table (phdr).
  // We check that the ELF magic is found, that the ELF class matches
  // our own, and that the program header table as defined in the ELF
  // headers fits in the buffer we read.
  if ((read(fd, elf.buf, bufsize) <= 0) ||
      (memcmp(elf.buf, ELFMAG, 4)) ||
      (elf.ehdr.e_ident[EI_CLASS] != ELFCLASS) ||
      // Upcast e_phentsize so the multiplication is done in the same precision
      // as the subsequent addition, to satisfy static analyzers and avoid
      // issues with abnormally large program header tables.
      (elf.ehdr.e_phoff + (static_cast<Elf_Off>(elf.ehdr.e_phentsize) *
                           elf.ehdr.e_phnum) >= bufsize)) {
    close(fd);
    return;
  }
  // The program header table contains segment definitions. One such
  // segment type is PT_LOAD, which describes how the dynamic loader
  // is going to map the file in memory. We use that information to
  // find the biggest offset from the library that will be mapped in
  // memory.
  Elf_Phdr* phdr = (Elf_Phdr*)&elf.buf[elf.ehdr.e_phoff];
  Elf_Off end = 0;
  for (int phnum = elf.ehdr.e_phnum; phnum; phdr++, phnum--) {
    if ((phdr->p_type == PT_LOAD) &&
        (end < phdr->p_offset + phdr->p_filesz)) {
      end = phdr->p_offset + phdr->p_filesz;
    }
  }
  // Let the kernel read ahead what the dynamic loader is going to
  // map in memory soon after.
  if (end > 0) {
    ReadAhead(fd, 0, end);
  }
  close(fd);
#endif
}

void
mozilla::ReadAheadFile(mozilla::pathstr_t aFilePath, const size_t aOffset,
                       const size_t aCount, mozilla::filedesc_t* aOutFd)
{
#if defined(XP_WIN)
  if (!aFilePath) {
    if (aOutFd) {
      *aOutFd = INVALID_HANDLE_VALUE;
    }
    return;
  }
  HANDLE fd = CreateFileW(aFilePath, GENERIC_READ, FILE_SHARE_READ, nullptr,
                          OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN, nullptr);
  if (aOutFd) {
    *aOutFd = fd;
  }
  if (fd == INVALID_HANDLE_VALUE) {
    return;
  }
  ReadAhead(fd, aOffset, aCount);
  if (!aOutFd) {
    CloseHandle(fd);
  }
#elif defined(LINUX) || defined(XP_SOLARIS)
  if (!aFilePath) {
    if (aOutFd) {
      *aOutFd = -1;
    }
    return;
  }
  int fd = open(aFilePath, O_RDONLY);
  if (aOutFd) {
    *aOutFd = fd;
  }
  if (fd < 0) {
    return;
  }
  size_t count;
  if (aCount == SIZE_MAX) {
    struct stat st;
    if (fstat(fd, &st) < 0) {
      if (!aOutFd) {
        close(fd);
      }
      return;
    }
    count = st.st_size;
  } else {
    count = aCount;
  }
  ReadAhead(fd, aOffset, count);
  if (!aOutFd) {
    close(fd);
  }
#endif
}