Use pread() in FileDataLoader.

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }

extension/data_loader/file_data_loader.cpp

@@ -23,10 +23,20 @@
 #include <executorch/runtime/core/result.h>
 #include <executorch/runtime/platform/log.h>
 
+// Some platforms (e.g. Xtensa) do not support pread() that we use to read the
+// file at different offsets simultaneously from multiple threads not affecting
+// each other. We list them below and use a workaround for them.
+#if defined(__xtensa__)
+#define ET_HAVE_PREAD 0
+#endif // defined(__xtensa__)
+
+#ifndef ET_HAVE_PREAD
+#define ET_HAVE_PREAD 1
+#endif // !ET_HAVE_PREAD
+
 namespace torch {
 namespace executor {
 namespace util {
-
 namespace {
 
 /**
@@ -226,29 +236,28 @@ ET_NODISCARD Error FileDataLoader::load_into(
  ET_CHECK_OR_RETURN_ERROR(
  buffer != nullptr, InvalidArgument, "Provided buffer cannot be null");
 
- // Seek to the right place in the file.
- off_t seek_offset = ::lseek(fd_, offset, SEEK_SET);
- if (seek_offset != offset) {
- ET_LOG(
- Error,
- "Seeking %s to offset %zu returned %zd: %s",
- file_name_,
- offset,
- (ssize_t)seek_offset,
- strerror(errno));
- return Error::AccessFailed;
- }
-
  // Read the data into the aligned address.
  size_t needed = size;
  uint8_t* buf = reinterpret_cast<uint8_t*>(buffer);
+
+ // Make a duplicate fd if pread() is not available and we have to seek().
+ // Cannot use the standard dup() or fcntl() calls because the returned
+ // duplicate will share the underlying file record and affect the original fd
+ // when seeking on multiple threads simultaneously.
+ const auto dup_fd = ET_HAVE_PREAD ? fd_ : ::open(file_name_, O_RDONLY);
+
  while (needed > 0) {
- // Reads on macos will fail with EINVAL if size > INT32_MAX.
- ssize_t nread = ::read(
- fd_,
- buf,
- std::min<size_t>(
- needed, static_cast<size_t>(std::numeric_limits<int32_t>::max())));
+ // Reads on macOS will fail with EINVAL if size > INT32_MAX.
+ const auto chunk_size = std::min<size_t>(
+ needed, static_cast<size_t>(std::numeric_limits<int32_t>::max()));
+ const auto nread =
+#if ET_HAVE_PREAD
+ ::pread(dup_fd, buf, chunk_size, offset);
+#else
+ (::lseek(dup_fd, offset, SEEK_SET) == (off_t)-1)
+ ? -1
+ : ::read(dup_fd, buf, chunk_size);
+#endif
  if (nread < 0 && errno == EINTR) {
  // Interrupted by a signal; zero bytes read.
  continue;
@@ -263,10 +272,17 @@ ET_NODISCARD Error FileDataLoader::load_into(
  size,
  offset,
  nread == 0 ? "EOF" : strerror(errno));
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
+ }
  return Error::AccessFailed;
  }
  needed -= nread;
  buf += nread;
+ offset += nread;
+ }
+ if (!ET_HAVE_PREAD) {
+ ::close(dup_fd);
  }
  return Error::Ok;
 }