text: /*
  
  Copyright (c) 2003-2016, Arvid Norberg
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:
  
      * Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.
      * Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in
        the documentation and/or other materials provided with the distribution.
      * Neither the name of the author nor the names of its
        contributors may be used to endorse or promote products derived
        from this software without specific prior written permission.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE.
  
  */
  
  #ifdef __GNUC__
  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wunused-macros"
  #endif
  
  #ifdef __clang__
  #pragma clang diagnostic push
  #pragma clang diagnostic ignored "-Wunused-macros"
  #endif
  
  // these defines are just in case the system we're on needs them for 64 bit file
  // support
  #define _FILE_OFFSET_BITS 64
  #define _LARGE_FILES 1
  
  // on mingw this is necessary to enable 64-bit time_t, specifically used for
  // the stat struct. Without this, modification times returned by stat may be
  // incorrect and consistently fail resume data
  #ifndef __MINGW_USE_VC2005_COMPAT
  # define __MINGW_USE_VC2005_COMPAT
  #endif
  
  #ifdef __clang__
  #pragma clang diagnostic pop
  #endif
  
  #ifdef __GNUC__
  #pragma GCC diagnostic pop
  #endif
  
  #include "libtorrent/config.hpp"
  #include "libtorrent/alloca.hpp"
  #include "libtorrent/allocator.hpp" // page_size
  #include "libtorrent/file.hpp"
  #include <cstring>
  #include <vector>
  
  #ifdef TORRENT_DEBUG_FILE_LEAKS
  #include <set>
  #endif
  
  // for convert_to_wstring and convert_to_native
  #include "libtorrent/aux_/escape_string.hpp"
  #include <stdio.h>
  #include "libtorrent/assert.hpp"
  
  #include <boost/scoped_ptr.hpp>
  #include <boost/static_assert.hpp>
  
  #ifdef TORRENT_DISK_STATS
  #include "libtorrent/io.hpp"
  #endif
  
  #include <sys/stat.h>
  
  #ifdef TORRENT_WINDOWS
  // windows part
  
  #ifndef PtrToPtr64
  #define PtrToPtr64(x) (x)
  #endif
  
  #include "libtorrent/utf8.hpp"
  
  #ifndef WIN32_LEAN_AND_MEAN
  #define WIN32_LEAN_AND_MEAN
  #endif
  #include <windows.h>
  #include <winioctl.h>
  #ifndef TORRENT_MINGW
  #include <direct.h> // for _getcwd, _mkdir
  #else
  #include <dirent.h>
  #endif
  #include <sys/types.h>
  #else
  // posix part
  
  #include <unistd.h>
  #include <sys/types.h>
  #include <errno.h>
  #include <dirent.h>
  
  #ifdef TORRENT_LINUX
  // linux specifics
  
  #ifdef TORRENT_ANDROID
  #include <sys/vfs.h>
  #define statvfs statfs
  #define fstatvfs fstatfs
  #else
  #include <sys/statvfs.h>
  #endif
  
  #include <sys/ioctl.h>
  #ifdef TORRENT_ANDROID
  #include <sys/syscall.h>
  #define lseek lseek64
  #endif
  
  #elif defined __APPLE__ && defined __MACH__ && MAC_OS_X_VERSION_MIN_REQUIRED >= 1050
  // mac specifics
  
  #include <copyfile.h>
  
  #endif
  
  #undef _FILE_OFFSET_BITS
  
  // make sure the _FILE_OFFSET_BITS define worked
  // on this platform. It's supposed to make file
  // related functions support 64-bit offsets.
  // this test makes sure lseek() returns a type
  // at least 64 bits wide
  BOOST_STATIC_ASSERT(sizeof(lseek(0, 0, 0)) >= 8);
  
  #endif // posix part
  
  #if TORRENT_USE_PREADV
  # if defined TORRENT_WINDOWS
  namespace
  {
  	// wrap the windows function in something that looks
  	// like preadv() and pwritev()
  
  	// windows only lets us wait for 64 handles at a time, so this function makes
  	// sure we wait for all of them, partially in sequence
  	int wait_for_multiple_objects(int num_handles, HANDLE* h)
  	{
  		int batch_size = (std::min)(num_handles, MAXIMUM_WAIT_OBJECTS);
  		while (WaitForMultipleObjects(batch_size, h, TRUE, INFINITE) != WAIT_FAILED)
  		{
  			h += batch_size;
  			num_handles -= batch_size;
  			batch_size = (std::min)(num_handles, MAXIMUM_WAIT_OBJECTS);
  			if (batch_size <= 0) return WAIT_OBJECT_0;
  		}
  		return WAIT_FAILED;
  	}
  
  	int preadv(HANDLE fd, libtorrent::file::iovec_t const* bufs, int num_bufs, boost::int64_t file_offset)
  	{
  		OVERLAPPED* ol = TORRENT_ALLOCA(OVERLAPPED, num_bufs);
  		memset(ol, 0, sizeof(OVERLAPPED) * num_bufs);
  
  		HANDLE* h = TORRENT_ALLOCA(HANDLE, num_bufs);
  
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			ol[i].OffsetHigh = file_offset >> 32;
  			ol[i].Offset = file_offset & 0xffffffff;
  			ol[i].hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
  			h[i] = ol[i].hEvent;
  			if (h[i] == NULL)
  			{
  				// we failed to create the event, roll-back and return an error
  				for (int j = 0; j < i; ++j) CloseHandle(h[i]);
  				return -1;
  			}
  			file_offset += bufs[i].iov_len;
  		}
  
  		int ret = 0;
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			DWORD num_read;
  			if (ReadFile(fd, bufs[i].iov_base, DWORD(bufs[i].iov_len), &num_read, &ol[i]) == FALSE
  				&& GetLastError() != ERROR_IO_PENDING
  #ifdef ERROR_CANT_WAIT
  				&& GetLastError() != ERROR_CANT_WAIT
  #endif
  				)
  			{
  				ret = -1;
  				goto done;
  			}
  		}
  
  		if (wait_for_multiple_objects(num_bufs, h) == WAIT_FAILED)
  		{
  			ret = -1;
  			goto done;
  		}
  
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			if (WaitForSingleObject(ol[i].hEvent, INFINITE) == WAIT_FAILED)
  			{
  				ret = -1;
  				break;
  			}
  			DWORD num_read;
  			if (GetOverlappedResult(fd, &ol[i], &num_read, FALSE) == FALSE)
  			{
  #ifdef ERROR_CANT_WAIT
  				TORRENT_ASSERT(GetLastError() != ERROR_CANT_WAIT);
  #endif
  				ret = -1;
  				break;
  			}
  			ret += num_read;
  		}
  done:
  
  		for (int i = 0; i < num_bufs; ++i)
  			CloseHandle(h[i]);
  
  		return ret;
  	}
  
  	int pwritev(HANDLE fd, libtorrent::file::iovec_t const* bufs, int num_bufs, boost::int64_t file_offset)
  	{
  		OVERLAPPED* ol = TORRENT_ALLOCA(OVERLAPPED, num_bufs);
  		memset(ol, 0, sizeof(OVERLAPPED) * num_bufs);
  
  		HANDLE* h = TORRENT_ALLOCA(HANDLE, num_bufs);
  
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			ol[i].OffsetHigh = file_offset >> 32;
  			ol[i].Offset = file_offset & 0xffffffff;
  			ol[i].hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
  			h[i] = ol[i].hEvent;
  			if (h[i] == NULL)
  			{
  				// we failed to create the event, roll-back and return an error
  				for (int j = 0; j < i; ++j) CloseHandle(h[i]);
  				return -1;
  			}
  			file_offset += bufs[i].iov_len;
  		}
  
  		int ret = 0;
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			DWORD num_written;
  			if (WriteFile(fd, bufs[i].iov_base, DWORD(bufs[i].iov_len), &num_written, &ol[i]) == FALSE
  				&& GetLastError() != ERROR_IO_PENDING
  #ifdef ERROR_CANT_WAIT
  				&& GetLastError() != ERROR_CANT_WAIT
  #endif
  				)
  			{
  				ret = -1;
  				goto done;
  			}
  		}
  
  		if (wait_for_multiple_objects(num_bufs, h) == WAIT_FAILED)
  		{
  			ret = -1;
  			goto done;
  		}
  
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			if (WaitForSingleObject(ol[i].hEvent, INFINITE) == WAIT_FAILED)
  			{
  				ret = -1;
  				break;
  			}
  			DWORD num_written;
  			if (GetOverlappedResult(fd, &ol[i], &num_written, FALSE) == FALSE)
  			{
  #ifdef ERROR_CANT_WAIT
  				TORRENT_ASSERT(GetLastError() != ERROR_CANT_WAIT);
  #endif
  				ret = -1;
  				break;
  			}
  			ret += num_written;
  		}
  done:
  
  		for (int i = 0; i < num_bufs; ++i)
  			CloseHandle(h[i]);
  
  		return ret;
  	}
  }
  # else
  #  undef _BSD_SOURCE
  #  define _BSD_SOURCE // deprecated since glibc 2.20
  #  undef _DEFAULT_SOURCE
  #  define _DEFAULT_SOURCE
  #  include <sys/uio.h>
  # endif
  #endif
  
  #ifdef TORRENT_DEBUG
  BOOST_STATIC_ASSERT((libtorrent::file::rw_mask & libtorrent::file::sparse) == 0);
  BOOST_STATIC_ASSERT((libtorrent::file::rw_mask & libtorrent::file::attribute_mask) == 0);
  BOOST_STATIC_ASSERT((libtorrent::file::sparse & libtorrent::file::attribute_mask) == 0);
  #endif
  
  #if defined TORRENT_WINDOWS && defined UNICODE && !TORRENT_USE_WSTRING
  
  #ifdef _MSC_VER
  #pragma message ( "wide character support not available. Files will be saved using narrow string names" )
  #else
  #warning "wide character support not available. Files will be saved using narrow string names"
  #endif
  
  #endif // TORRENT_WINDOWS
  
  namespace libtorrent
  {
  	int bufs_size(file::iovec_t const* bufs, int num_bufs)
  	{
  		std::size_t size = 0;
  		for (file::iovec_t const* i = bufs, *end(bufs + num_bufs); i < end; ++i)
  			size += i->iov_len;
  		return int(size);
  	}
  
  #ifdef TORRENT_WINDOWS
  	std::string convert_separators(std::string p)
  	{
  		for (int i = 0; i < int(p.size()); ++i)
  			if (p[i] == '/') p[i] = '\\';
  		return p;
  	}
  
  	time_t file_time_to_posix(FILETIME f)
  	{
  		const boost::uint64_t posix_time_offset = 11644473600LL;
  		boost::uint64_t ft = (boost::uint64_t(f.dwHighDateTime) << 32)
  			| f.dwLowDateTime;
  
  		// windows filetime is specified in 100 nanoseconds resolution.
  		// convert to seconds
  		return time_t(ft / 10000000 - posix_time_offset);
  	}
  #endif
  
  	void stat_file(std::string const& inf, file_status* s
  		, error_code& ec, int flags)
  	{
  		ec.clear();
  #ifdef TORRENT_WINDOWS
  
  		TORRENT_UNUSED(flags);
  
  		std::string p = convert_separators(inf);
  #if TORRENT_USE_UNC_PATHS
  		// UNC paths must be absolute
  		// network paths are already UNC paths
  		if (inf.substr(0,2) == "\\\\") p = inf;
  		else p = "\\\\?\\" + (is_complete(p) ? p : combine_path(current_working_directory(), p));
  #endif
  
  #if TORRENT_USE_WSTRING
  #define CreateFile_ CreateFileW
  		std::wstring f = convert_to_wstring(p);
  #else
  #define CreateFile_ CreateFileA
  		std::string f = convert_to_native(p);
  #endif
  
  		// in order to open a directory, we need the FILE_FLAG_BACKUP_SEMANTICS
  		HANDLE h = CreateFile_(f.c_str(), 0, FILE_SHARE_DELETE | FILE_SHARE_READ
  			| FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
  
  		if (h == INVALID_HANDLE_VALUE)
  		{
  			ec.assign(GetLastError(), system_category());
  			TORRENT_ASSERT(ec);
  			return;
  		}
  
  		BY_HANDLE_FILE_INFORMATION data;
  		if (!GetFileInformationByHandle(h, &data))
  		{
  			ec.assign(GetLastError(), system_category());
  			TORRENT_ASSERT(ec);
  			CloseHandle(h);
  			return;
  		}
  
  		s->file_size = (boost::uint64_t(data.nFileSizeHigh) << 32) | data.nFileSizeLow;
  		s->ctime = file_time_to_posix(data.ftCreationTime);
  		s->atime = file_time_to_posix(data.ftLastAccessTime);
  		s->mtime = file_time_to_posix(data.ftLastWriteTime);
  
  		s->mode = (data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)
  			? file_status::directory
  			: (data.dwFileAttributes & FILE_ATTRIBUTE_DEVICE)
  			? file_status::character_special : file_status::regular_file;
  		CloseHandle(h);
  #else
  
  		// posix version
  
  		std::string const& f = convert_to_native(inf);
  
  		struct stat ret;
  		int retval;
  		if (flags & dont_follow_links)
  			retval = ::lstat(f.c_str(), &ret);
  		else
  			retval = ::stat(f.c_str(), &ret);
  		if (retval < 0)
  		{
  			ec.assign(errno, system_category());
  			return;
  		}
  
  		s->file_size = ret.st_size;
  		s->atime = ret.st_atime;
  		s->mtime = ret.st_mtime;
  		s->ctime = ret.st_ctime;
  
  		s->mode = (S_ISREG(ret.st_mode) ? file_status::regular_file : 0)
  			| (S_ISDIR(ret.st_mode) ? file_status::directory : 0)
  			| (S_ISLNK(ret.st_mode) ? file_status::link : 0)
  			| (S_ISFIFO(ret.st_mode) ? file_status::fifo : 0)
  			| (S_ISCHR(ret.st_mode) ? file_status::character_special : 0)
  			| (S_ISBLK(ret.st_mode) ? file_status::block_special : 0)
  			| (S_ISSOCK(ret.st_mode) ? file_status::socket : 0);
  
  #endif // TORRENT_WINDOWS
  	}
  
  	void rename(std::string const& inf, std::string const& newf, error_code& ec)
  	{
  		ec.clear();
  
  #if TORRENT_USE_WSTRING && defined TORRENT_WINDOWS
  		std::wstring f1 = convert_to_wstring(inf);
  		std::wstring f2 = convert_to_wstring(newf);
  		if (_wrename(f1.c_str(), f2.c_str()) < 0)
  #else
  		std::string const& f1 = convert_to_native(inf);
  		std::string const& f2 = convert_to_native(newf);
  		if (::rename(f1.c_str(), f2.c_str()) < 0)
  #endif
  		{
  			ec.assign(errno, generic_category());
  			return;
  		}
  	}
  
  	void create_directories(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  		if (is_directory(f, ec)) return;
  		if (ec != boost::system::errc::no_such_file_or_directory)
  			return;
  		ec.clear();
  		if (is_root_path(f)) return;
  		if (has_parent_path(f))
  		{
  			create_directories(parent_path(f), ec);
  			if (ec) return;
  		}
  		create_directory(f, ec);
  	}
  
  	void create_directory(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  
  #ifdef TORRENT_WINDOWS
  #if TORRENT_USE_WSTRING
  #define CreateDirectory_ CreateDirectoryW
  		std::wstring n = convert_to_wstring(f);
  #else
  #define CreateDirectory_ CreateDirectoryA
  		std::string const& n = convert_to_native(f);
  #endif // TORRENT_USE_WSTRING
  
  		if (CreateDirectory_(n.c_str(), 0) == 0
  			&& GetLastError() != ERROR_ALREADY_EXISTS)
  			ec.assign(GetLastError(), system_category());
  #else
  		std::string n = convert_to_native(f);
  		int ret = mkdir(n.c_str(), 0777);
  		if (ret < 0 && errno != EEXIST)
  			ec.assign(errno, system_category());
  #endif
  	}
  
  	void hard_link(std::string const& file, std::string const& link
  		, error_code& ec)
  	{
  #ifdef TORRENT_WINDOWS
  
  #if TORRENT_USE_WSTRING
  #define CreateHardLink_ CreateHardLinkW
  		std::wstring n_exist = convert_to_wstring(file);
  		std::wstring n_link = convert_to_wstring(link);
  #else
  #define CreateHardLink_ CreateHardLinkA
  		std::string n_exist = convert_to_native(file);
  		std::string n_link = convert_to_native(link);
  #endif
  		BOOL ret = CreateHardLink_(n_link.c_str(), n_exist.c_str(), NULL);
  		if (ret)
  		{
  			ec.clear();
  			return;
  		}
  
  		// something failed. Does the filesystem not support hard links?
  		// TODO: 3 find out what error code is reported when the filesystem
  		// does not support hard links.
  		DWORD error = GetLastError();
  		if (error != ERROR_NOT_SUPPORTED && error != ERROR_ACCESS_DENIED)
  		{
  			// it's possible CreateHardLink will copy the file internally too,
  			// if the filesystem does not support it.
  			ec.assign(GetLastError(), system_category());
  			return;
  		}
  
  		// fall back to making a copy
  
  #else
  
  		std::string n_exist = convert_to_native(file);
  		std::string n_link = convert_to_native(link);
  
  		// assume posix's link() function exists
  		int ret = ::link(n_exist.c_str(), n_link.c_str());
  
  		if (ret == 0)
  		{
  			ec.clear();
  			return;
  		}
  
  		// most errors are passed through, except for the ones that indicate that
  		// hard links are not supported and require a copy.
  		// TODO: 2 test this on a FAT volume to see what error we get!
  		if (errno != EMLINK || errno != EXDEV)
  		{
  			// some error happened, report up to the caller
  			ec.assign(errno, system_category());
  			return;
  		}
  
  		// fall back to making a copy
  
  #endif
  
  		// if we get here, we should copy the file
  		copy_file(file, link, ec);
  	}
  
  	bool is_directory(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  		error_code e;
  		file_status s;
  		stat_file(f, &s, e);
  		if (!e && s.mode & file_status::directory) return true;
  		ec = e;
  		return false;
  	}
  
  	void recursive_copy(std::string const& old_path, std::string const& new_path, error_code& ec)
  	{
  		TORRENT_ASSERT(!ec);
  		if (is_directory(old_path, ec))
  		{
  			create_directory(new_path, ec);
  			if (ec) return;
  			for (directory i(old_path, ec); !i.done(); i.next(ec))
  			{
  				std::string f = i.file();
  				if (f == ".." || f == ".") continue;
  				recursive_copy(combine_path(old_path, f), combine_path(new_path, f), ec);
  				if (ec) return;
  			}
  		}
  		else if (!ec)
  		{
  			copy_file(old_path, new_path, ec);
  		}
  	}
  
  	void copy_file(std::string const& inf, std::string const& newf, error_code& ec)
  	{
  		ec.clear();
  #ifdef TORRENT_WINDOWS
  #if TORRENT_USE_WSTRING
  #define CopyFile_ CopyFileW
  		std::wstring f1 = convert_to_wstring(inf);
  		std::wstring f2 = convert_to_wstring(newf);
  #else
  #define CopyFile_ CopyFileA
  		std::string const& f1 = convert_to_native(inf);
  		std::string const& f2 = convert_to_native(newf);
  #endif
  
  		if (CopyFile_(f1.c_str(), f2.c_str(), false) == 0)
  			ec.assign(GetLastError(), system_category());
  #elif defined __APPLE__ && defined __MACH__ && MAC_OS_X_VERSION_MIN_REQUIRED >= 1050
  		std::string f1 = convert_to_native(inf);
  		std::string f2 = convert_to_native(newf);
  
  		// this only works on 10.5
  		copyfile_state_t state = copyfile_state_alloc();
  		if (copyfile(f1.c_str(), f2.c_str(), state, COPYFILE_ALL) < 0)
  			ec.assign(errno, system_category());
  		copyfile_state_free(state);
  #else
  		std::string f1 = convert_to_native(inf);
  		std::string f2 = convert_to_native(newf);
  
  		int infd = ::open(f1.c_str(), O_RDONLY);
  		if (infd < 0)
  		{
  			ec.assign(errno, system_category());
  			return;
  		}
  
  		// rely on default umask to filter x and w permissions
  		// for group and others
  		int permissions = S_IRUSR | S_IWUSR
  			| S_IRGRP | S_IWGRP
  			| S_IROTH | S_IWOTH;
  
  		int outfd = ::open(f2.c_str(), O_WRONLY | O_CREAT, permissions);
  		if (outfd < 0)
  		{
  			close(infd);
  			ec.assign(errno, system_category());
  			return;
  		}
  		char buffer[4096];
  		for (;;)
  		{
  			int num_read = read(infd, buffer, sizeof(buffer));
  			if (num_read == 0) break;
  			if (num_read < 0)
  			{
  				ec.assign(errno, system_category());
  				break;
  			}
  			int num_written = write(outfd, buffer, num_read);
  			if (num_written < num_read)
  			{
  				ec.assign(errno, system_category());
  				break;
  			}
  			if (num_read < int(sizeof(buffer))) break;
  		}
  		close(infd);
  		close(outfd);
  #endif // TORRENT_WINDOWS
  	}
  
  	void move_file(std::string const& inf, std::string const& newf, error_code& ec)
  	{
  		ec.clear();
  
  		file_status s;
  		stat_file(inf, &s, ec);
  		if (ec) return;
  
  		if (has_parent_path(newf))
  		{
  			create_directories(parent_path(newf), ec);
  			if (ec) return;
  		}
  
  		rename(inf, newf, ec);
  
  		// on OSX, the error when trying to rename a file across different
  		// volumes is EXDEV, which will make it fall back to copying.
  
  		if (ec)
  		{
  			if (ec != boost::system::errc::no_such_file_or_directory
  				&& ec != boost::system::errc::invalid_argument
  				&& ec != boost::system::errc::permission_denied)
  			{
  				ec.clear();
  				copy_file(inf, newf, ec);
  
  				if (!ec)
  				{
  					// ignore errors when removing
  					error_code ignore;
  					remove(inf, ignore);
  				}
  			}
  		}
  	}
  
  	std::string split_path(std::string const& f)
  	{
  		if (f.empty()) return f;
  
  		std::string ret;
  		char const* start = f.c_str();
  		char const* p = start;
  		while (*start != 0)
  		{
  			while (*p != '/'
  				&& *p != '\0'
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  				&& *p != '\\'
  #endif
  				) ++p;
  			if (p - start > 0)
  			{
  				ret.append(start, p - start);
  				ret.append(1, '\0');
  			}
  			if (*p != 0) ++p;
  			start = p;
  		}
  		ret.append(1, '\0');
  		return ret;
  	}
  
  	char const* next_path_element(char const* p)
  	{
  		p += strlen(p) + 1;
  		if (*p == 0) return 0;
  		return p;
  	}
  
  	std::string extension(std::string const& f)
  	{
  		for (int i = int(f.size()) - 1; i >= 0; --i)
  		{
  			if (f[i] == '/') break;
  #ifdef TORRENT_WINDOWS
  			if (f[i] == '\\') break;
  #endif
  			if (f[i] != '.') continue;
  			return f.substr(i);
  		}
  		return "";
  	}
  
  	std::string remove_extension(std::string const& f)
  	{
  		char const* slash = strrchr(f.c_str(), '/');
  #ifdef TORRENT_WINDOWS
  		slash = (std::max)((char const*)strrchr(f.c_str(), '\\'), slash);
  #endif
  		char const* ext = strrchr(f.c_str(), '.');
  		// if we don't have an extension, just return f
  		if (ext == 0 || ext == &f[0] || (slash != NULL && ext < slash)) return f;
  		return f.substr(0, ext - &f[0]);
  	}
  
  	void replace_extension(std::string& f, std::string const& ext)
  	{
  		for (int i = int(f.size()) - 1; i >= 0; --i)
  		{
  			if (f[i] == '/') break;
  #ifdef TORRENT_WINDOWS
  			if (f[i] == '\\') break;
  #endif
  
  			if (f[i] != '.') continue;
  
  			f.resize(i);
  			break;
  		}
  		f += '.';
  		f += ext;
  	}
  
  	bool is_root_path(std::string const& f)
  	{
  		if (f.empty()) return false;
  
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  		// match \\ form
  		if (f == "\\\\") return true;
  		int i = 0;
  		// match the xx:\ or xx:/ form
  		while (f[i] && is_alpha(f[i])) ++i;
  		if (i == int(f.size()-2) && f[i] == ':' && (f[i+1] == '\\' || f[i+1] == '/'))
  			return true;
  		// match network paths \\computer_name\ form
  		if (f.size() > 2 && f[0] == '\\' && f[1] == '\\')
  		{
  			// we don't care about the last character, since it's OK for it
  			// to be a slash or a back slash
  			bool found = false;
  			for (int j = 2; j < int(f.size()) - 1; ++j)
  			{
  				if (f[j] != '\\' && f[j] != '/') continue;
  				// there is a directory separator in here,
  				// i.e. this is not the root
  				found = true;
  				break;
  			}
  			if (!found) return true;
  		}
  #else
  		// as well as parent_path("/") should be "/".
  		if (f == "/") return true;
  #endif
  		return false;
  	}
  
  	bool has_parent_path(std::string const& f)
  	{
  		if (f.empty()) return false;
  		if (is_root_path(f)) return false;
  
  		int len = int(f.size()) - 1;
  		// if the last character is / or \ ignore it
  		if (f[len] == '/' || f[len] == '\\') --len;
  		while (len >= 0)
  		{
  			if (f[len] == '/' || f[len] == '\\')
  				break;
  			--len;
  		}
  
  		return len >= 0;
  	}
  
  	std::string parent_path(std::string const& f)
  	{
  		if (f.empty()) return f;
  
  #ifdef TORRENT_WINDOWS
  		if (f == "\\\\") return "";
  #endif
  		if (f == "/") return "";
  
  		int len = int(f.size());
  		// if the last character is / or \ ignore it
  		if (f[len-1] == '/' || f[len-1] == '\\') --len;
  		while (len > 0)
  		{
  			--len;
  			if (f[len] == '/' || f[len] == '\\')
  				break;
  		}
  
  		if (f[len] == '/' || f[len] == '\\') ++len;
  		return std::string(f.c_str(), len);
  	}
  
  	char const* filename_cstr(char const* f)
  	{
  		if (f == 0) return f;
  
  		char const* sep = strrchr(f, '/');
  #ifdef TORRENT_WINDOWS
  		char const* altsep = strrchr(f, '\\');
  		if (sep == 0 || altsep > sep) sep = altsep;
  #endif
  		if (sep == 0) return f;
  		return sep+1;
  	}
  
  	std::string filename(std::string const& f)
  	{
  		if (f.empty()) return "";
  		char const* first = f.c_str();
  		char const* sep = strrchr(first, '/');
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  		char const* altsep = strrchr(first, '\\');
  		if (sep == 0 || altsep > sep) sep = altsep;
  #endif
  		if (sep == 0) return f;
  
  		if (sep - first == int(f.size()) - 1)
  		{
  			// if the last character is a / (or \)
  			// ignore it
  			int len = 0;
  			while (sep > first)
  			{
  				--sep;
  				if (*sep == '/'
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  					|| *sep == '\\'
  #endif
  					)
  					return std::string(sep + 1, len);
  				++len;
  			}
  			return std::string(first, len);
  
  		}
  		return std::string(sep + 1);
  	}
  
  	void append_path(std::string& branch, std::string const& leaf)
  	{
  		append_path(branch, leaf.c_str(), int(leaf.size()));
  	}
  
  	void append_path(std::string& branch
  		, char const* str, int len)
  	{
  		TORRENT_ASSERT(!is_complete(std::string(str, len)));
  		if (branch.empty() || branch == ".")
  		{
  			branch.assign(str, len);
  			return;
  		}
  		if (len == 0) return;
  
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  #define TORRENT_SEPARATOR_CHAR '\\'
  		bool need_sep = branch[branch.size()-1] != '\\'
  			&& branch[branch.size()-1] != '/';
  #else
  #define TORRENT_SEPARATOR_CHAR '/'
  		bool need_sep = branch[branch.size()-1] != '/';
  #endif
  
  		if (need_sep) branch += TORRENT_SEPARATOR_CHAR;
  		branch.append(str, len);
  	}
  
  	std::string combine_path(std::string const& lhs, std::string const& rhs)
  	{
  		TORRENT_ASSERT(!is_complete(rhs));
  		if (lhs.empty() || lhs == ".") return rhs;
  		if (rhs.empty() || rhs == ".") return lhs;
  
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  #define TORRENT_SEPARATOR "\\"
  		bool need_sep = lhs[lhs.size()-1] != '\\' && lhs[lhs.size()-1] != '/';
  #else
  #define TORRENT_SEPARATOR "/"
  		bool need_sep = lhs[lhs.size()-1] != '/';
  #endif
  		std::string ret;
  		int target_size = int(lhs.size() + rhs.size() + 2);
  		ret.resize(target_size);
  		target_size = snprintf(&ret[0], target_size, "%s%s%s", lhs.c_str()
  			, (need_sep?TORRENT_SEPARATOR:""), rhs.c_str());
  		ret.resize(target_size);
  		return ret;
  	}
  
  	std::string current_working_directory()
  	{
  #if defined TORRENT_WINDOWS && !defined TORRENT_MINGW
  #if TORRENT_USE_WSTRING
  		wchar_t cwd[TORRENT_MAX_PATH];
  		_wgetcwd(cwd, sizeof(cwd) / sizeof(wchar_t));
  #else
  		char cwd[TORRENT_MAX_PATH];
  		_getcwd(cwd, sizeof(cwd));
  #endif // TORRENT_USE_WSTRING
  #else
  		char cwd[TORRENT_MAX_PATH];
  		if (getcwd(cwd, sizeof(cwd)) == 0) return "/";
  #endif
  #if defined TORRENT_WINDOWS && !defined TORRENT_MINGW && TORRENT_USE_WSTRING
  		return convert_from_wstring(cwd);
  #else
  		return convert_from_native(cwd);
  #endif
  	}
  
  #if TORRENT_USE_UNC_PATHS
  	std::string canonicalize_path(std::string const& f)
  	{
  		std::string ret;
  		ret.resize(f.size());
  		char* write_cur = &ret[0];
  		char* last_write_sep = write_cur;
  
  		char const* read_cur = f.c_str();
  		char const* last_read_sep = read_cur;
  
  		// the last_*_sep pointers point to one past
  		// the last path separator encountered and is
  		// initializes to the first character in the path
  		while (*read_cur)
  		{
  			if (*read_cur != '\\')
  			{
  				*write_cur++ = *read_cur++;
  				continue;
  			}
  			int element_len = read_cur - last_read_sep;
  			if (element_len == 1 && memcmp(last_read_sep, ".", 1) == 0)
  			{
  				--write_cur;
  				++read_cur;
  				last_read_sep = read_cur;
  				continue;
  			}
  			if (element_len == 2 && memcmp(last_read_sep, "..", 2) == 0)
  			{
  				// find the previous path separator
  				if (last_write_sep > &ret[0])
  				{
  					--last_write_sep;
  					while (last_write_sep > &ret[0]
  						&& last_write_sep[-1] != '\\')
  						--last_write_sep;
  				}
  				write_cur = last_write_sep;
  				// find the previous path separator
  				if (last_write_sep > &ret[0])
  				{
  					--last_write_sep;
  					while (last_write_sep > &ret[0]
  						&& last_write_sep[-1] != '\\')
  						--last_write_sep;
  				}
  				++read_cur;
  				last_read_sep = read_cur;
  				continue;
  			}
  			*write_cur++ = *read_cur++;
  			last_write_sep = write_cur;
  			last_read_sep = read_cur;
  		}
  		// terminate destination string
  		*write_cur = 0;
  		ret.resize(write_cur - &ret[0]);
  		return ret;
  	}
  #endif
  
  	boost::int64_t file_size(std::string const& f)
  	{
  		error_code ec;
  		file_status s;
  		stat_file(f, &s, ec);
  		if (ec) return 0;
  		return s.file_size;
  	}
  
  	bool exists(std::string const& f, error_code& ec)
  	{
  		file_status s;
  		stat_file(f, &s, ec);
  		if (ec)
  		{
  			if (ec == boost::system::errc::no_such_file_or_directory)
  				ec.clear();
  			return false;
  		}
  		return true;
  	}
  
  	bool exists(std::string const& f)
  	{
  		error_code ec;
  		return exists(f, ec);
  	}
  
  	void remove(std::string const& inf, error_code& ec)
  	{
  		ec.clear();
  
  #ifdef TORRENT_WINDOWS
  		// windows does not allow trailing / or \ in
  		// the path when removing files
  		std::string pruned;
  		if (inf[inf.size() - 1] == '/'
  			|| inf[inf.size() - 1] == '\\')
  			pruned = inf.substr(0, inf.size() - 1);
  		else
  			pruned = inf;
  #if TORRENT_USE_WSTRING
  #define DeleteFile_ DeleteFileW
  #define RemoveDirectory_ RemoveDirectoryW
  		std::wstring f = convert_to_wstring(pruned);
  #else
  #define DeleteFile_ DeleteFileA
  #define RemoveDirectory_ RemoveDirectoryA
  		std::string f = convert_to_native(pruned);
  #endif
  		if (DeleteFile_(f.c_str()) == 0)
  		{
  			if (GetLastError() == ERROR_ACCESS_DENIED)
  			{
  				if (RemoveDirectory_(f.c_str()) != 0)
  					return;
  			}
  			ec.assign(GetLastError(), system_category());
  			return;
  		}
  #else // TORRENT_WINDOWS
  		std::string const& f = convert_to_native(inf);
  		if (::remove(f.c_str()) < 0)
  		{
  			ec.assign(errno, system_category());
  			return;
  		}
  #endif // TORRENT_WINDOWS
  	}
  
  	void remove_all(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  
  		file_status s;
  		stat_file(f, &s, ec);
  		if (ec) return;
  
  		if (s.mode & file_status::directory)
  		{
  			for (directory i(f, ec); !i.done(); i.next(ec))
  			{
  				if (ec) return;
  				std::string p = i.file();
  				if (p == "." || p == "..") continue;
  				remove_all(combine_path(f, p), ec);
  				if (ec) return;
  			}
  		}
  		remove(f, ec);
  	}
  
  	std::string complete(std::string const& f)
  	{
  		if (is_complete(f)) return f;
  		if (f == ".") return current_working_directory();
  		return combine_path(current_working_directory(), f);
  	}
  
  	bool is_complete(std::string const& f)
  	{
  		if (f.empty()) return false;
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  		int i = 0;
  		// match the xx:\ or xx:/ form
  		while (f[i] && is_alpha(f[i])) ++i;
  		if (i < int(f.size()-1) && f[i] == ':' && (f[i+1] == '\\' || f[i+1] == '/'))
  			return true;
  
  		// match the \\ form
  		if (int(f.size()) >= 2 && f[0] == '\\' && f[1] == '\\')
  			return true;
  		return false;
  #else
  		if (f[0] == '/') return true;
  		return false;
  #endif
  	}
  
  	directory::directory(std::string const& path, error_code& ec)
  		: m_done(false)
  	{
  		ec.clear();
  #ifdef TORRENT_WINDOWS
  		m_inode = 0;
  		// the path passed to FindFirstFile() must be
  		// a pattern
  		std::string f = convert_separators(path);
  		if (!f.empty() && f[f.size()-1] != '\\') f += "\\*";
  		else f += "*";
  #if TORRENT_USE_WSTRING
  #define FindFirstFile_ FindFirstFileW
  		std::wstring p = convert_to_wstring(f);
  #else
  #define FindFirstFile_ FindFirstFileA
  		std::string p = convert_to_native(f);
  #endif
  		m_handle = FindFirstFile_(p.c_str(), &m_fd);
  		if (m_handle == INVALID_HANDLE_VALUE)
  		{
  			ec.assign(GetLastError(), system_category());
  			m_done = true;
  			return;
  		}
  #else
  
  		memset(&m_dirent, 0, sizeof(dirent));
  		m_name[0] = 0;
  
  		// the path passed to opendir() may not
  		// end with a /
  		std::string p = path;
  		if (!path.empty() && path[path.size()-1] == '/')
  			p.resize(path.size()-1);
  
  		p = convert_to_native(p);
  		m_handle = opendir(p.c_str());
  		if (m_handle == 0)
  		{
  			ec.assign(errno, system_category());
  			m_done = true;
  			return;
  		}
  		// read the first entry
  		next(ec);
  #endif
  	}
  
  	directory::~directory()
  	{
  #ifdef TORRENT_WINDOWS
  		if (m_handle != INVALID_HANDLE_VALUE)
  			FindClose(m_handle);
  #else
  		if (m_handle) closedir(m_handle);
  #endif
  	}
  
  	boost::uint64_t directory::inode() const
  	{
  #ifdef TORRENT_WINDOWS
  		return m_inode;
  #else
  		return m_dirent.d_ino;
  #endif
  	}
  
  	std::string directory::file() const
  	{
  #ifdef TORRENT_WINDOWS
  #if TORRENT_USE_WSTRING
  		return convert_from_wstring(m_fd.cFileName);
  #else
  		return convert_from_native(m_fd.cFileName);
  #endif
  #else
  		return convert_from_native(m_dirent.d_name);
  #endif
  	}
  
  	void directory::next(error_code& ec)
  	{
  		ec.clear();
  #ifdef TORRENT_WINDOWS
  #if TORRENT_USE_WSTRING
  #define FindNextFile_ FindNextFileW
  #else
  #define FindNextFile_ FindNextFileA
  #endif
  		if (FindNextFile_(m_handle, &m_fd) == 0)
  		{
  			m_done = true;
  			int err = GetLastError();
  			if (err != ERROR_NO_MORE_FILES)
  				ec.assign(err, system_category());
  		}
  		++m_inode;
  #else
  		dirent* dummy;
  		if (readdir_r(m_handle, &m_dirent, &dummy) != 0)
  		{
  			ec.assign(errno, system_category());
  			m_done = true;
  		}
  		if (dummy == 0) m_done = true;
  #endif
  	}
  
  #ifndef INVALID_HANDLE_VALUE
  #define INVALID_HANDLE_VALUE -1
  #endif
  
  #ifdef TORRENT_WINDOWS
  	struct overlapped_t
  	{
  		overlapped_t()
  		{
  			memset(&ol, 0, sizeof(ol));
  			ol.hEvent = CreateEvent(0, true, false, 0);
  		}
  		~overlapped_t()
  		{
  			if (ol.hEvent != INVALID_HANDLE_VALUE)
  				CloseHandle(ol.hEvent);
  		}
  		int wait(HANDLE file, error_code& ec)
  		{
  			if (ol.hEvent != INVALID_HANDLE_VALUE
  				&& WaitForSingleObject(ol.hEvent, INFINITE) == WAIT_FAILED)
  			{
  				ec.assign(GetLastError(), system_category());
  				return -1;
  			}
  
  			DWORD ret = -1;
  			if (GetOverlappedResult(file, &ol, &ret, false) == 0)
  			{
  				DWORD last_error = GetLastError();
  				if (last_error != ERROR_HANDLE_EOF)
  				{
  #ifdef ERROR_CANT_WAIT
  					TORRENT_ASSERT(last_error != ERROR_CANT_WAIT);
  #endif
  					ec.assign(last_error, system_category());
  					return -1;
  				}
  			}
  			return ret;
  		}
  
  		OVERLAPPED ol;
  	};
  #endif // TORRENT_WINDOWS
  
  
  #ifdef TORRENT_WINDOWS
  	bool get_manage_volume_privs();
  
  	// this needs to be run before CreateFile
  	bool file::has_manage_volume_privs = get_manage_volume_privs();
  #endif
  
  	file::file()
  		: m_file_handle(INVALID_HANDLE_VALUE)
  		, m_open_mode(0)
  	{
  #ifdef TORRENT_DISK_STATS
  		m_file_id = 0;
  #endif
  	}
  
  	file::file(std::string const& path, int mode, error_code& ec)
  		: m_file_handle(INVALID_HANDLE_VALUE)
  		, m_open_mode(0)
  	{
  #ifdef TORRENT_DISK_STATS
  		m_file_id = 0;
  #endif
  		// the return value is not important, since the
  		// error code contains the same information
  		open(path, mode, ec);
  	}
  
  	file::~file()
  	{
  		close();
  	}
  
  #ifdef TORRENT_DISK_STATS
  	namespace
  	{
  		boost::uint32_t silly_hash(std::string const& str)
  		{
  			boost::uint32_t ret = 1;
  			for (int i = 0; i < str.size(); ++i)
  			{
  				if (str[i] == 0) continue;
  					ret *= int(str[i]);
  			}
  			return ret;
  		}
  	}
  #endif
  
  	bool file::open(std::string const& path, int mode, error_code& ec)
  	{
  		close();
  
  #ifdef TORRENT_DEBUG_FILE_LEAKS
  		m_file_path = path;
  #endif
  
  #ifdef TORRENT_DISK_STATS
  		m_file_id = silly_hash(path);
  #endif
  
  #ifdef TORRENT_WINDOWS
  
  		struct open_mode_t
  		{
  			DWORD rw_mode;
  			DWORD create_mode;
  		};
  
  		static const open_mode_t mode_array[] =
  		{
  			// read_only
  			{GENERIC_READ, OPEN_EXISTING},
  			// write_only
  			{GENERIC_WRITE, OPEN_ALWAYS},
  			// read_write
  			{GENERIC_WRITE | GENERIC_READ, OPEN_ALWAYS},
  		};
  
  		static const DWORD attrib_array[] =
  		{
  			FILE_ATTRIBUTE_NORMAL, // no attrib
  			FILE_ATTRIBUTE_HIDDEN, // hidden
  			FILE_ATTRIBUTE_NORMAL, // executable
  			FILE_ATTRIBUTE_HIDDEN, // hidden + executable
  		};
  
  		std::string p = convert_separators(path);
  #if TORRENT_USE_UNC_PATHS
  		// UNC paths must be absolute
  		// network paths are already UNC paths
  		if (path.substr(0,2) == "\\\\") p = path;
  		else p = "\\\\?\\" + (is_complete(p) ? p : combine_path(current_working_directory(), p));
  #endif
  
  #if TORRENT_USE_WSTRING
  #define CreateFile_ CreateFileW
  		std::wstring file_path = convert_to_wstring(p);
  #else
  #define CreateFile_ CreateFileA
  		std::string file_path = convert_to_native(p);
  #endif
  
  		TORRENT_ASSERT((mode & rw_mask) < sizeof(mode_array)/sizeof(mode_array[0]));
  		open_mode_t const& m = mode_array[mode & rw_mask];
  		DWORD a = attrib_array[(mode & attribute_mask) >> 12];
  
  		// one might think it's a good idea to pass in FILE_FLAG_RANDOM_ACCESS. It
  		// turns out that it isn't. That flag will break your operating system:
  		// http://support.microsoft.com/kb/2549369
  
  		DWORD flags = ((mode & random_access) ? 0 : FILE_FLAG_SEQUENTIAL_SCAN)
  			| (a ? a : FILE_ATTRIBUTE_NORMAL)
  			| FILE_FLAG_OVERLAPPED
  			| ((mode & no_cache) ? FILE_FLAG_WRITE_THROUGH : 0);
  
  		handle_type handle = CreateFile_(file_path.c_str(), m.rw_mode
  			, (mode & lock_file) ? FILE_SHARE_READ : FILE_SHARE_READ | FILE_SHARE_WRITE
  			, 0, m.create_mode, flags, 0);
  
  		if (handle == INVALID_HANDLE_VALUE)
  		{
  			ec.assign(GetLastError(), system_category());
  			TORRENT_ASSERT(ec);
  			return false;
  		}
  
  		m_file_handle = handle;
  
  		// try to make the file sparse if supported
  		// only set this flag if the file is opened for writing
  		if ((mode & file::sparse) && (mode & rw_mask) != read_only)
  		{
  			DWORD temp;
  			overlapped_t ol;
  			BOOL ret = ::DeviceIoControl(native_handle(), FSCTL_SET_SPARSE, 0, 0
  				, 0, 0, &temp, &ol.ol);
  			error_code error;
  			if (ret == FALSE && GetLastError() == ERROR_IO_PENDING)
  				ol.wait(native_handle(), error);
  		}
  #else // TORRENT_WINDOWS
  
  		// rely on default umask to filter x and w permissions
  		// for group and others
  		int permissions = S_IRUSR | S_IWUSR
  			| S_IRGRP | S_IWGRP
  			| S_IROTH | S_IWOTH;
  
  		if (mode & attribute_executable)
  			permissions |= S_IXGRP | S_IXOTH | S_IXUSR;
  #ifdef O_BINARY
  		static const int mode_array[] = {O_RDONLY | O_BINARY, O_WRONLY | O_CREAT | O_BINARY, O_RDWR | O_CREAT | O_BINARY};
  #else
  		static const int mode_array[] = {O_RDONLY, O_WRONLY | O_CREAT, O_RDWR | O_CREAT};
  #endif
  
  		int open_mode = 0
  #ifdef O_NOATIME
  			| ((mode & no_atime) ? O_NOATIME : 0)
  #endif
  #ifdef O_SYNC
  			| ((mode & no_cache) ? O_SYNC: 0)
  #endif
  			;
  
  		handle_type handle = ::open(convert_to_native(path).c_str()
  			, mode_array[mode & rw_mask] | open_mode
  			, permissions);
  
  #ifdef O_NOATIME
  		// O_NOATIME is not allowed for files we don't own
  		// so, if we get EPERM when we try to open with it
  		// try again without O_NOATIME
  		if (handle == -1 && (mode & no_atime) && errno == EPERM)
  		{
  			mode &= ~no_atime;
  			open_mode &= ~O_NOATIME;
  			handle = ::open(path.c_str(), mode_array[mode & rw_mask] | open_mode
  				, permissions);
  		}
  #endif
  		if (handle == -1)
  		{
  			ec.assign(errno, system_category());
  			TORRENT_ASSERT(ec);
  			return false;
  		}
  
  		m_file_handle = handle;
  
  		// The purpose of the lock_file flag is primarily to prevent other
  		// processes from corrupting files that are being used by libtorrent.
  		// the posix file locking mechanism does not prevent others from
  		// accessing files, unless they also attempt to lock the file. That's
  		// why the SETLK mechanism is not used here.
  
  #ifdef DIRECTIO_ON
  		// for solaris
  		if (mode & no_cache)
  		{
  			int yes = 1;
  			directio(native_handle(), DIRECTIO_ON);
  		}
  #endif
  
  #ifdef F_NOCACHE
  		// for BSD/Mac
  		if (mode & no_cache)
  		{
  			int yes = 1;
  			fcntl(native_handle(), F_NOCACHE, &yes);
  
  #ifdef F_NODIRECT
  			// it's OK to temporarily cache written pages
  			fcntl(native_handle(), F_NODIRECT, &yes);
  #endif
  		}
  #endif
  
  #ifdef POSIX_FADV_RANDOM
  		if (mode & random_access)
  		{
  			// disable read-ahead
  			posix_fadvise(native_handle(), 0, 0, POSIX_FADV_RANDOM);
  		}
  #endif
  
  #endif
  		m_open_mode = mode;
  
  		TORRENT_ASSERT(is_open());
  		return true;
  	}
  
  #ifdef TORRENT_DEBUG_FILE_LEAKS
  	void file::print_info(FILE* out) const
  	{
  		if (!is_open()) return;
  		fprintf(out, "\n===> FILE: %s\n", m_file_path.c_str());
  	}
  #endif
  
  	bool file::is_open() const
  	{
  		return m_file_handle != INVALID_HANDLE_VALUE;
  	}
  
  #ifdef TORRENT_WINDOWS
  	// returns true if the given file has any regions that are
  	// sparse, i.e. not allocated.
  	bool is_sparse(HANDLE file)
  	{
  		LARGE_INTEGER file_size;
  		if (!GetFileSizeEx(file, &file_size))
  			return false;
  
  		overlapped_t ol;
  		if (ol.ol.hEvent == NULL) return false;
  
  #ifdef TORRENT_MINGW
  typedef struct _FILE_ALLOCATED_RANGE_BUFFER {
  	LARGE_INTEGER FileOffset;
  	LARGE_INTEGER Length;
  } FILE_ALLOCATED_RANGE_BUFFER, *PFILE_ALLOCATED_RANGE_BUFFER;
  #define FSCTL_QUERY_ALLOCATED_RANGES ((0x9 << 16) | (1 << 14) | (51 << 2) | 3)
  #endif
  		FILE_ALLOCATED_RANGE_BUFFER in;
  		in.FileOffset.QuadPart = 0;
  		in.Length.QuadPart = file_size.QuadPart;
  
  		FILE_ALLOCATED_RANGE_BUFFER out[2];
  
  		DWORD returned_bytes = 0;
  		BOOL ret = DeviceIoControl(file, FSCTL_QUERY_ALLOCATED_RANGES, (void*)&in, sizeof(in)
  			, out, sizeof(out), &returned_bytes, &ol.ol);
  
  		if (ret == FALSE && GetLastError() == ERROR_IO_PENDING)
  		{
  			error_code ec;
  			returned_bytes = ol.wait(file, ec);
  			if (ec) return true;
  		}
  		else if (ret == FALSE)
  		{
  //			int error = GetLastError();
  			return true;
  		}
  
  		// if we have more than one range in the file, we're sparse
  		if (returned_bytes != sizeof(FILE_ALLOCATED_RANGE_BUFFER)) {
  			return true;
  		}
  
  		return (in.Length.QuadPart != out[0].Length.QuadPart);
  	}
  #endif
  
  	void file::close()
  	{
  #ifdef TORRENT_DISK_STATS
  		m_file_id = 0;
  #endif
  
  		if (!is_open()) return;
  
  #ifdef TORRENT_WINDOWS
  
  		// if this file is open for writing, has the sparse
  		// flag set, but there are no sparse regions, unset
  		// the flag
  		int rw_mode = m_open_mode & rw_mask;
  		if ((rw_mode != read_only)
  			&& (m_open_mode & sparse)
  			&& !is_sparse(native_handle()))
  		{
  			overlapped_t ol;
  			// according to MSDN, clearing the sparse flag of a file only
  			// works on windows vista and later
  #ifdef TORRENT_MINGW
  			typedef struct _FILE_SET_SPARSE_BUFFER {
  				BOOLEAN SetSparse;
  			} FILE_SET_SPARSE_BUFFER, *PFILE_SET_SPARSE_BUFFER;
  #endif
  			DWORD temp;
  			FILE_SET_SPARSE_BUFFER b;
  			b.SetSparse = FALSE;
  			BOOL ret = ::DeviceIoControl(native_handle(), FSCTL_SET_SPARSE, &b, sizeof(b)
  				, 0, 0, &temp, &ol.ol);
  			error_code ec;
  			if (ret == FALSE && GetLastError() == ERROR_IO_PENDING)
  			{
  				ol.wait(native_handle(), ec);
  			}
  		}
  
  		CloseHandle(native_handle());
  #else
  		if (m_file_handle != INVALID_HANDLE_VALUE)
  			::close(m_file_handle);
  #endif
  
  		m_file_handle = INVALID_HANDLE_VALUE;
  
  		m_open_mode = 0;
  	}
  
  	namespace {
  
  	void gather_copy(file::iovec_t const* bufs, int num_bufs, char* dst)
  	{
  		std::size_t offset = 0;
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			memcpy(dst + offset, bufs[i].iov_base, bufs[i].iov_len);
  			offset += bufs[i].iov_len;
  		}
  	}
  
  	void scatter_copy(file::iovec_t const* bufs, int num_bufs, char const* src)
  	{
  		std::size_t offset = 0;
  		for (int i = 0; i < num_bufs; ++i)
  		{
  			memcpy(bufs[i].iov_base, src + offset, bufs[i].iov_len);
  			offset += bufs[i].iov_len;
  		}
  	}
  
  #if !TORRENT_USE_PREADV
  	bool coalesce_read_buffers(file::iovec_t const*& bufs, int& num_bufs
  		, file::iovec_t* tmp)
  	{
  		int const buf_size = bufs_size(bufs, num_bufs);
  		char* buf = static_cast<char*>(malloc(buf_size));
  		if (!buf) return false;
  		tmp->iov_base = buf;
  		tmp->iov_len = buf_size;
  		bufs = tmp;
  		num_bufs = 1;
  		return true;
  	}
  
  	void coalesce_read_buffers_end(file::iovec_t const* bufs, int const num_bufs
  		, char* const buf, bool const copy)
  	{
  		if (copy) scatter_copy(bufs, num_bufs, buf);
  		free(buf);
  	}
  
  	bool coalesce_write_buffers(file::iovec_t const*& bufs, int& num_bufs
  		, file::iovec_t* tmp)
  	{
  		int const buf_size = bufs_size(bufs, num_bufs);
  		char* buf = static_cast<char*>(malloc(buf_size));
  		if (!buf) return false;
  		gather_copy(bufs, num_bufs, buf);
  		tmp->iov_base = buf;
  		tmp->iov_len = buf_size;
  		bufs = tmp;
  		num_bufs = 1;
  		return true;
  	}
  #endif // TORRENT_USE_PREADV
  
  	template <class Fun>
  	boost::int64_t iov(Fun f, handle_type fd, boost::int64_t file_offset, file::iovec_t const* bufs_in
  		, int num_bufs_in, error_code& ec)
  	{
  		file::iovec_t const* bufs = bufs_in;
  		int num_bufs = num_bufs_in;
  
  #if TORRENT_USE_PREADV
  
  		int ret = 0;
  		while (num_bufs > 0)
  		{
  			int nbufs = (std::min)(num_bufs, TORRENT_IOV_MAX);
  			int tmp_ret = 0;
  			tmp_ret = f(fd, bufs, nbufs, file_offset);
  			if (tmp_ret < 0)
  			{
  #ifdef TORRENT_WINDOWS
  				ec.assign(GetLastError(), system_category());
  #else
  				ec.assign(errno, system_category());
  #endif
  				return -1;
  			}
  			file_offset += tmp_ret;
  			ret += tmp_ret;
  
  			// we got a short read/write. It's either 0, and we're at EOF, or we
  			// just need to issue the read/write operation again. In either case,
  			// punt that to the upper layer, as reissuing the operations is
  			// complicated here
  			const int expected_len = bufs_size(bufs, nbufs);
  			if (tmp_ret < expected_len) break;
  
  			num_bufs -= nbufs;
  			bufs += nbufs;
  		}
  		return ret;
  
  #elif TORRENT_USE_PREAD
  
  		int ret = 0;
  		for (file::iovec_t const* i = bufs, *end(bufs + num_bufs); i < end; ++i)
  		{
  			int tmp_ret = f(fd, i->iov_base, i->iov_len, file_offset);
  			if (tmp_ret < 0)
  			{
  #ifdef TORRENT_WINDOWS
  				ec.assign(GetLastError(), system_category());
  #else
  				ec.assign(errno, system_category());
  #endif
  				return -1;
  			}
  			file_offset += tmp_ret;
  			ret += tmp_ret;
  			if (tmp_ret < int(i->iov_len)) break;
  		}
  
  		return ret;
  
  #else // not PREADV nor PREAD
  
  		int ret = 0;
  
  #ifdef TORRENT_WINDOWS
  		if (SetFilePointerEx(fd, offs, &offs, FILE_BEGIN) == FALSE)
  		{
  			ec.assign(GetLastError(), system_category());
  			return -1;
  		}
  #else
  		if (lseek(fd, file_offset, SEEK_SET) < 0)
  		{
  			ec.assign(errno, system_category());
  			return -1;
  		}
  #endif
  
  		for (file::iovec_t const* i = bufs, *end(bufs + num_bufs); i < end; ++i)
  		{
  			int tmp_ret = f(fd, i->iov_base, i->iov_len);
  			if (tmp_ret < 0)
  			{
  #ifdef TORRENT_WINDOWS
  				ec.assign(GetLastError(), system_category());
  #else
  				ec.assign(errno, system_category());
  #endif
  				return -1;
  			}
  			file_offset += tmp_ret;
  			ret += tmp_ret;
  			if (tmp_ret < int(i->iov_len)) break;
  		}
  
  		return ret;
  
  #endif
  	}
  
  	} // anonymous namespace
  
  	// this has to be thread safe and atomic. i.e. on posix systems it has to be
  	// turned into a series of pread() calls
  	boost::int64_t file::readv(boost::int64_t file_offset, iovec_t const* bufs, int num_bufs
  		, error_code& ec, int flags)
  	{
  		if (m_file_handle == INVALID_HANDLE_VALUE)
  		{
  #ifdef TORRENT_WINDOWS
  			ec = error_code(ERROR_INVALID_HANDLE, system_category());
  #else
  			ec = error_code(boost::system::errc::bad_file_descriptor, generic_category());
  #endif
  			return -1;
  		}
  		TORRENT_ASSERT((m_open_mode & rw_mask) == read_only || (m_open_mode & rw_mask) == read_write);
  		TORRENT_ASSERT(bufs);
  		TORRENT_ASSERT(num_bufs > 0);
  		TORRENT_ASSERT(is_open());
  
  #if TORRENT_USE_PREADV
  		TORRENT_UNUSED(flags);
  
  		int ret = iov(&::preadv, native_handle(), file_offset, bufs, num_bufs, ec);
  #else
  
  		// there's no point in coalescing single buffer writes
  		if (num_bufs == 1)
  		{
  			flags &= ~file::coalesce_buffers;
  		}
  
  		file::iovec_t tmp;
  		file::iovec_t const* const orig_bufs = bufs;
  		int const orig_num_bufs = num_bufs;
  		if ((flags & file::coalesce_buffers))
  		{
  			if (!coalesce_read_buffers(bufs, num_bufs, &tmp))
  				// ok, that failed, don't coalesce this read
  				flags &= ~file::coalesce_buffers;
  		}
  
  #if TORRENT_USE_PREAD
  		int ret = iov(&::pread, native_handle(), file_offset, bufs, num_bufs, ec);
  #else
  		int ret = iov(&::read, native_handle(), file_offset, bufs, num_bufs, ec);
  #endif
  
  		if ((flags & file::coalesce_buffers))
  			coalesce_read_buffers_end(orig_bufs, orig_num_bufs
  				, static_cast<char*>(tmp.iov_base), !ec);
  
  #endif
  		return ret;
  	}
  
  	// This has to be thread safe, i.e. atomic.
  	// that means, on posix this has to be turned into a series of
  	// pwrite() calls
  	boost::int64_t file::writev(boost::int64_t file_offset, iovec_t const* bufs, int num_bufs
  		, error_code& ec, int flags)
  	{
  		if (m_file_handle == INVALID_HANDLE_VALUE)
  		{
  #ifdef TORRENT_WINDOWS
  			ec = error_code(ERROR_INVALID_HANDLE, system_category());
  #else
  			ec = error_code(boost::system::errc::bad_file_descriptor, generic_category());
  #endif
  			return -1;
  		}
  		TORRENT_ASSERT((m_open_mode & rw_mask) == write_only || (m_open_mode & rw_mask) == read_write);
  		TORRENT_ASSERT(bufs);
  		TORRENT_ASSERT(num_bufs > 0);
  		TORRENT_ASSERT(is_open());
  
  		ec.clear();
  
  #if TORRENT_USE_PREADV
  		TORRENT_UNUSED(flags);
  
  		int ret = iov(&::pwritev, native_handle(), file_offset, bufs, num_bufs, ec);
  #else
  
  		// there's no point in coalescing single buffer writes
  		if (num_bufs == 1)
  		{
  			flags &= ~file::coalesce_buffers;
  		}
  
  		file::iovec_t tmp;
  		if (flags & file::coalesce_buffers)
  		{
  			if (!coalesce_write_buffers(bufs, num_bufs, &tmp))
  				// ok, that failed, don't coalesce writes
  				flags &= ~file::coalesce_buffers;
  		}
  
  #if TORRENT_USE_PREAD
  		int ret = iov(&::pwrite, native_handle(), file_offset, bufs, num_bufs, ec);
  #else
  		int ret = iov(&::write, native_handle(), file_offset, bufs, num_bufs, ec);
  #endif
  
  		if (flags & file::coalesce_buffers)
  			free(tmp.iov_base);
  
  #endif
  #if TORRENT_USE_FDATASYNC \
  	&& !defined F_NOCACHE && \
  	!defined DIRECTIO_ON
  		if (m_open_mode & no_cache)
  		{
  			if (fdatasync(native_handle()) != 0
  				&& errno != EINVAL
  				&& errno != ENOSYS)
  			{
  				ec.assign(errno, system_category());
  			}
  		}
  #endif
  		return ret;
  	}
  
  #ifdef TORRENT_WINDOWS
  	bool get_manage_volume_privs()
  	{
  		typedef BOOL (WINAPI *OpenProcessToken_t)(
  			HANDLE ProcessHandle,
  			DWORD DesiredAccess,
  			PHANDLE TokenHandle);
  
  		typedef BOOL (WINAPI *LookupPrivilegeValue_t)(
  			LPCSTR lpSystemName,
  			LPCSTR lpName,
  			PLUID lpLuid);
  
  		typedef BOOL (WINAPI *AdjustTokenPrivileges_t)(
  			HANDLE TokenHandle,
  			BOOL DisableAllPrivileges,
  			PTOKEN_PRIVILEGES NewState,
  			DWORD BufferLength,
  			PTOKEN_PRIVILEGES PreviousState,
  			PDWORD ReturnLength);
  
  		static OpenProcessToken_t pOpenProcessToken = NULL;
  		static LookupPrivilegeValue_t pLookupPrivilegeValue = NULL;
  		static AdjustTokenPrivileges_t pAdjustTokenPrivileges = NULL;
  		static bool failed_advapi = false;
  
  		if (pOpenProcessToken == NULL && !failed_advapi)
  		{
  			HMODULE advapi = LoadLibraryA("advapi32");
  			if (advapi == NULL)
  			{
  				failed_advapi = true;
  				return false;
  			}
  			pOpenProcessToken = (OpenProcessToken_t)GetProcAddress(advapi, "OpenProcessToken");
  			pLookupPrivilegeValue = (LookupPrivilegeValue_t)GetProcAddress(advapi, "LookupPrivilegeValueA");
  			pAdjustTokenPrivileges = (AdjustTokenPrivileges_t)GetProcAddress(advapi, "AdjustTokenPrivileges");
  			if (pOpenProcessToken == NULL
  				|| pLookupPrivilegeValue == NULL
  				|| pAdjustTokenPrivileges == NULL)
  			{
  				failed_advapi = true;
  				return false;
  			}
  		}
  
  		HANDLE token;
  		if (!pOpenProcessToken(GetCurrentProcess()
  			, TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &token))
  			return false;
  
  		TOKEN_PRIVILEGES privs;
  		if (!pLookupPrivilegeValue(NULL, "SeManageVolumePrivilege"
  			, &privs.Privileges[0].Luid))
  		{
  			CloseHandle(token);
  			return false;
  		}
  
  		privs.PrivilegeCount = 1;
  		privs.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
  
  		bool ret = pAdjustTokenPrivileges(token, FALSE, &privs, 0, NULL, NULL)
  			&& GetLastError() == ERROR_SUCCESS;
  
  		CloseHandle(token);
  
  		return ret;
  	}
  
  	void set_file_valid_data(HANDLE f, boost::int64_t size)
  	{
  		typedef BOOL (WINAPI *SetFileValidData_t)(HANDLE, LONGLONG);
  		static SetFileValidData_t pSetFileValidData = NULL;
  		static bool failed_kernel32 = false;
  
  		if (pSetFileValidData == NULL && !failed_kernel32)
  		{
  			HMODULE k32 = LoadLibraryA("kernel32");
  			if (k32 == NULL)
  			{
  				failed_kernel32 = true;
  				return;
  			}
  			pSetFileValidData = (SetFileValidData_t)GetProcAddress(k32, "SetFileValidData");
  			if (pSetFileValidData == NULL)
  			{
  				failed_kernel32 = true;
  				return;
  			}
  		}
  
  		TORRENT_ASSERT(pSetFileValidData);
  
  		// we don't necessarily expect to have enough
  		// privilege to do this, so ignore errors.
  		pSetFileValidData(f, size);
  	}
  #endif
  
  	bool file::set_size(boost::int64_t s, error_code& ec)
  	{
  		TORRENT_ASSERT(is_open());
  		TORRENT_ASSERT(s >= 0);
  
  #ifdef TORRENT_WINDOWS
  
  		LARGE_INTEGER offs;
  		LARGE_INTEGER cur_size;
  		if (GetFileSizeEx(native_handle(), &cur_size) == FALSE)
  		{
  			ec.assign(GetLastError(), system_category());
  			return false;
  		}
  		offs.QuadPart = s;
  		// only set the file size if it's not already at
  		// the right size. We don't want to update the
  		// modification time if we don't have to
  		if (cur_size.QuadPart != s)
  		{
  			if (SetFilePointerEx(native_handle(), offs, &offs, FILE_BEGIN) == FALSE)
  			{
  				ec.assign(GetLastError(), system_category());
  				return false;
  			}
  			if (::SetEndOfFile(native_handle()) == FALSE)
  			{
  				ec.assign(GetLastError(), system_category());
  				return false;
  			}
  		}
  
  #if _WIN32_WINNT >= 0x0600 // only if Windows Vista or newer
  		if ((m_open_mode & sparse) == 0)
  		{
  			typedef DWORD (WINAPI *GetFileInformationByHandleEx_t)(HANDLE hFile
  				, FILE_INFO_BY_HANDLE_CLASS FileInformationClass
  				, LPVOID lpFileInformation
  				, DWORD dwBufferSize);
  
  			static GetFileInformationByHandleEx_t GetFileInformationByHandleEx_ = NULL;
  
  			static bool failed_kernel32 = false;
  
  			if ((GetFileInformationByHandleEx_ == NULL) && !failed_kernel32)
  			{
  				HMODULE kernel32 = LoadLibraryA("kernel32.dll");
  				if (kernel32)
  				{
  					GetFileInformationByHandleEx_ = (GetFileInformationByHandleEx_t)GetProcAddress(kernel32, "GetFileInformationByHandleEx");
  				}
  				else
  				{
  					failed_kernel32 = true;
  				}
  			}
  
  			offs.QuadPart = 0;
  			if (GetFileInformationByHandleEx_)
  			{
  				// only allocate the space if the file
  				// is not fully allocated
  				FILE_STANDARD_INFO inf;
  				if (GetFileInformationByHandleEx_(native_handle()
  					, FileStandardInfo, &inf, sizeof(inf)) == FALSE)
  				{
  					ec.assign(GetLastError(), system_category());
  					if (ec) return false;
  				}
  				offs = inf.AllocationSize;
  			}
  
  			if (offs.QuadPart != s)
  			{
  				// if the user has permissions, avoid filling
  				// the file with zeroes, but just fill it with
  				// garbage instead
  				set_file_valid_data(m_file_handle, s);
  			}
  		}
  #endif // if Windows Vista
  #else // NON-WINDOWS
  		struct stat st;
  		if (fstat(native_handle(), &st) != 0)
  		{
  			ec.assign(errno, system_category());
  			return false;
  		}
  
  		// only truncate the file if it doesn't already
  		// have the right size. We don't want to update
  		if (st.st_size != s && ftruncate(native_handle(), s) < 0)
  		{
  			ec.assign(errno, system_category());
  			return false;
  		}
  
  		// if we're not in sparse mode, allocate the storage
  		// but only if the number of allocated blocks for the file
  		// is less than the file size. Otherwise we would just
  		// update the modification time of the file for no good
  		// reason.
  		if ((m_open_mode & sparse) == 0
  			&& st.st_blocks < (s + st.st_blksize - 1) / st.st_blksize)
  		{
  			// How do we know that the file is already allocated?
  			// if we always try to allocate the space, we'll update
  			// the modification time without actually changing the file
  			// but if we don't do anything if the file size is
  #ifdef F_PREALLOCATE
  			fstore_t f = {F_ALLOCATECONTIG, F_PEOFPOSMODE, 0, s, 0};
  			if (fcntl(native_handle(), F_PREALLOCATE, &f) < 0)
  			{
  				if (errno != ENOSPC)
  				{
  					ec.assign(errno, system_category());
  					return false;
  				}
  				// ok, let's try to allocate non contiguous space then
  				f.fst_flags = F_ALLOCATEALL;
  				if (fcntl(native_handle(), F_PREALLOCATE, &f) < 0)
  				{
  					ec.assign(errno, system_category());
  					return false;
  				}
  			}
  #endif // F_PREALLOCATE
  
  #ifdef F_ALLOCSP64
  			flock64 fl64;
  			fl64.l_whence = SEEK_SET;
  			fl64.l_start = 0;
  			fl64.l_len = s;
  			if (fcntl(native_handle(), F_ALLOCSP64, &fl64) < 0)
  			{
  				ec.assign(errno, system_category());
  				return false;
  			}
  
  #endif // F_ALLOCSP64
  
  #if TORRENT_HAS_FALLOCATE
  			// if fallocate failed, we have to use posix_fallocate
  			// which can be painfully slow
  			// if you get a compile error here, you might want to
  			// define TORRENT_HAS_FALLOCATE to 0.
  			int const ret = posix_fallocate(native_handle(), 0, s);
  			// posix_allocate fails with EINVAL in case the underlying
  			// filesystem does not support this operation
  			if (ret != 0 && ret != EINVAL)
  			{
  				ec.assign(ret, system_category());
  				return false;
  			}
  #endif // TORRENT_HAS_FALLOCATE
  		}
  #endif // TORRENT_WINDOWS
  		return true;
  	}
  
  	boost::int64_t file::get_size(error_code& ec) const
  	{
  #ifdef TORRENT_WINDOWS
  		LARGE_INTEGER file_size;
  		if (!GetFileSizeEx(native_handle(), &file_size))
  		{
  			ec.assign(GetLastError(), system_category());
  			return -1;
  		}
  		return file_size.QuadPart;
  #else
  		struct stat fs;
  		if (fstat(native_handle(), &fs) != 0)
  		{
  			ec.assign(errno, system_category());
  			return -1;
  		}
  		return fs.st_size;
  #endif
  	}
  
  	boost::int64_t file::sparse_end(boost::int64_t start) const
  	{
  #ifdef TORRENT_WINDOWS
  
  #ifdef TORRENT_MINGW
  typedef struct _FILE_ALLOCATED_RANGE_BUFFER {
  	LARGE_INTEGER FileOffset;
  	LARGE_INTEGER Length;
  } FILE_ALLOCATED_RANGE_BUFFER, *PFILE_ALLOCATED_RANGE_BUFFER;
  #define FSCTL_QUERY_ALLOCATED_RANGES ((0x9 << 16) | (1 << 14) | (51 << 2) | 3)
  #endif // TORRENT_MINGW
  
  		FILE_ALLOCATED_RANGE_BUFFER buffer;
  		DWORD bytes_returned = 0;
  		FILE_ALLOCATED_RANGE_BUFFER in;
  		error_code ec;
  		boost::int64_t file_size = get_size(ec);
  		if (ec) return start;
  
  		in.FileOffset.QuadPart = start;
  		in.Length.QuadPart = file_size - start;
  
  		if (!DeviceIoControl(native_handle(), FSCTL_QUERY_ALLOCATED_RANGES
  			, &in, sizeof(FILE_ALLOCATED_RANGE_BUFFER)
  			, &buffer, sizeof(FILE_ALLOCATED_RANGE_BUFFER), &bytes_returned, 0))
  		{
  			if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) return start;
  		}
  
  		// if there are no allocated regions within the rest
  		// of the file, return the end of the file
  		if (bytes_returned == 0) return file_size;
  
  		// assume that this range overlaps the start of the
  		// region we were interested in, and that start actually
  		// resides in an allocated region.
  		if (buffer.FileOffset.QuadPart < start) return start;
  
  		// return the offset to the next allocated region
  		return buffer.FileOffset.QuadPart;
  
  #elif defined SEEK_DATA
  		// this is supported on solaris
  		boost::int64_t ret = lseek(native_handle(), start, SEEK_DATA);
  		if (ret < 0) return start;
  		return start;
  #else
  		return start;
  #endif
  	}
  
  #ifdef TORRENT_DEBUG_FILE_LEAKS
  	std::set<file_handle*> global_file_handles;
  	std::mutex file_handle_mutex;
  
  	file_handle::file_handle()
  	{
  		std::lock_guard<std::mutex> l(file_handle_mutex);
  		global_file_handles.insert(this);
  		stack[0] = 0;
  	}
  	file_handle::file_handle(file* f): m_file(f)
  	{
  		std::lock_guard<std::mutex> l(file_handle_mutex);
  		global_file_handles.insert(this);
  		if (f) print_backtrace(stack, sizeof(stack), 10);
  		else stack[0] = 0;
  	}
  	file_handle::file_handle(file_handle const& fh)
  	{
  		std::lock_guard<std::mutex> l(file_handle_mutex);
  		global_file_handles.insert(this);
  		m_file = fh.m_file;
  		if (m_file) print_backtrace(stack, sizeof(stack), 10);
  		else stack[0] = 0;
  	}
  	file_handle::~file_handle()
  	{
  		std::lock_guard<std::mutex> l(file_handle_mutex);
  		global_file_handles.erase(this);
  		stack[0] = 0;
  	}
  	file* file_handle::operator->() { return m_file.get(); }
  	file const* file_handle::operator->() const { return m_file.get(); }
  	file& file_handle::operator*() { return *m_file.get(); }
  	file const& file_handle::operator*() const { return *m_file.get(); }
  	file* file_handle::get() { return m_file.get(); }
  	file const* file_handle::get() const { return m_file.get(); }
  	file_handle::operator bool() const { return m_file.get(); }
  	file_handle& file_handle::reset(file* f)
  	{
  		std::lock_guard<std::mutex> l(file_handle_mutex);
  		if (f) print_backtrace(stack, sizeof(stack), 10);
  		else stack[0] = 0;
  		l.unlock();
  		m_file.reset(f);
  		return *this;
  	}
  
  	void print_open_files(char const* event, char const* name)
  	{
  		FILE* out = fopen("open_files.log", "a+");
  		std::lock_guard<std::mutex> l(file_handle_mutex);
  		fprintf(out, "\n\nEVENT: %s TORRENT: %s\n\n", event, name);
  		for (std::set<file_handle*>::iterator i = global_file_handles.begin()
  			, end(global_file_handles.end()); i != end; ++i)
  		{
  			TORRENT_ASSERT(*i != NULL);
  			if (!*i) continue;
  			file_handle const& h = **i;
  			if (!h) continue;
  
  			if (!h->is_open()) continue;
  			h->print_info(out);
  			fprintf(out, "\n%s\n\n", h.stack);
  		}
  		fclose(out);
  	}
  #endif
  }
  
  