8b217d5313
The Linux feature allows writing new files to an invisible file, and then replace the old file. This preserves the old file if we get interrupted by some event.
187 lines
3.9 KiB
C++
187 lines
3.9 KiB
C++
/*
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* Copyright (C) 2003-2015 The Music Player Daemon Project
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* http://www.musicpd.org
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "config.h"
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#include "FileOutputStream.hxx"
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#include "fs/FileSystem.hxx"
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#include "util/Error.hxx"
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#ifdef WIN32
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FileOutputStream::FileOutputStream(Path _path, Error &error)
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:path(_path),
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handle(CreateFile(path.c_str(), GENERIC_WRITE, 0, nullptr,
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TRUNCATE_EXISTING,
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FILE_ATTRIBUTE_NORMAL|FILE_FLAG_WRITE_THROUGH,
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nullptr))
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{
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if (handle == INVALID_HANDLE_VALUE)
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error.FormatLastError("Failed to create %s", path.c_str());
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}
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bool
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FileOutputStream::Write(const void *data, size_t size, Error &error)
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{
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assert(IsDefined());
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DWORD nbytes;
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if (!WriteFile(handle, data, size, &nbytes, nullptr)) {
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error.FormatLastError("Failed to write to %s", path.c_str());
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return false;
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}
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if (size_t(nbytes) != size) {
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error.FormatLastError(ERROR_DISK_FULL,
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"Failed to write to %s", path.c_str());
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return false;
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}
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return true;
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}
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bool
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FileOutputStream::Commit(gcc_unused Error &error)
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{
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assert(IsDefined());
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CloseHandle(handle);
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return true;
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}
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void
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FileOutputStream::Cancel()
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{
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assert(IsDefined());
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CloseHandle(handle);
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RemoveFile(path);
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}
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#else
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#include <fcntl.h>
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#include <unistd.h>
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#include <errno.h>
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#ifdef HAVE_LINKAT
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#ifndef O_TMPFILE
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/* supported since Linux 3.11 */
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#define __O_TMPFILE 020000000
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#define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
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#include <stdio.h>
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#endif
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/**
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* Open a file using Linux's O_TMPFILE for writing the given file.
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*/
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static int
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OpenTempFile(Path path)
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{
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const auto directory = path.GetDirectoryName();
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if (directory.IsNull())
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return -1;
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return OpenFile(directory, O_TMPFILE|O_WRONLY, 0666);
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}
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#endif /* HAVE_LINKAT */
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FileOutputStream::FileOutputStream(Path _path, Error &error)
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:path(_path)
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{
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#ifdef HAVE_LINKAT
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/* try Linux's O_TMPFILE first */
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fd = OpenTempFile(path);
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is_tmpfile = fd >= 0;
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if (!is_tmpfile) {
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#endif
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/* fall back to plain POSIX */
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fd = OpenFile(path,
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O_WRONLY|O_CREAT|O_TRUNC,
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0666);
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if (fd < 0)
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error.FormatErrno("Failed to create %s", path.c_str());
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#ifdef HAVE_LINKAT
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}
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#endif
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}
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bool
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FileOutputStream::Write(const void *data, size_t size, Error &error)
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{
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assert(IsDefined());
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ssize_t nbytes = write(fd, data, size);
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if (nbytes < 0) {
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error.FormatErrno("Failed to write to %s", path.c_str());
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return false;
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} else if ((size_t)nbytes < size) {
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error.FormatErrno(ENOSPC,
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"Failed to write to %s", path.c_str());
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return false;
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}
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return true;
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}
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bool
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FileOutputStream::Commit(Error &error)
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{
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assert(IsDefined());
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#if HAVE_LINKAT
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if (is_tmpfile) {
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RemoveFile(path);
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/* hard-link the temporary file to the final path */
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char fd_path[64];
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snprintf(fd_path, sizeof(fd_path), "/proc/self/fd/%d", fd);
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if (linkat(AT_FDCWD, fd_path, AT_FDCWD, path.c_str(),
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AT_SYMLINK_FOLLOW) < 0) {
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error.FormatErrno("Failed to commit %s", path.c_str());
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close(fd);
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return false;
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}
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}
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#endif
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bool success = close(fd) == 0;
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fd = -1;
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if (!success)
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error.FormatErrno("Failed to commit %s", path.c_str());
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return success;
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}
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void
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FileOutputStream::Cancel()
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{
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assert(IsDefined());
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close(fd);
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fd = -1;
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#ifdef HAVE_LINKAT
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if (!is_tmpfile)
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#endif
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RemoveFile(path);
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}
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#endif
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