Add an unpatched version of xz, XZ Utils, to /trunk/deps/third_party

xz/src/xz/file_io.c

+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       file_io.c
+/// \brief      File opening, unlinking, and closing
+//
+//  Author:     Lasse Collin
+//
+//  This file has been put into the public domain.
+//  You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include "private.h"
+
+#include <fcntl.h>
+
+#ifdef TUKLIB_DOSLIKE
+#       include <io.h>
+#else
+static bool warn_fchown;
+#endif
+
+#if defined(HAVE_FUTIMES) || defined(HAVE_FUTIMESAT) || defined(HAVE_UTIMES)
+#       include <sys/time.h>
+#elif defined(HAVE_UTIME)
+#       include <utime.h>
+#endif
+
+#include "tuklib_open_stdxxx.h"
+
+#ifndef O_BINARY
+#       define O_BINARY 0
+#endif
+
+#ifndef O_NOCTTY
+#       define O_NOCTTY 0
+#endif
+
+
+/// If true, try to create sparse files when decompressing.
+static bool try_sparse = true;
+
+#ifndef TUKLIB_DOSLIKE
+/// File status flags of standard output. This is used by io_open_dest()
+/// and io_close_dest().
+static int stdout_flags = 0;
+#endif
+
+
+static bool io_write_buf(file_pair *pair, const uint8_t *buf, size_t size);
+
+
+extern void
+io_init(void)
+{
+        // Make sure that stdin, stdout, and and stderr are connected to
+        // a valid file descriptor. Exit immediately with exit code ERROR
+        // if we cannot make the file descriptors valid. Maybe we should
+        // print an error message, but our stderr could be screwed anyway.
+        tuklib_open_stdxxx(E_ERROR);
+
+#ifndef TUKLIB_DOSLIKE
+        // If fchown() fails setting the owner, we warn about it only if
+        // we are root.
+        warn_fchown = geteuid() == 0;
+#endif
+
+#ifdef __DJGPP__
+        // Avoid doing useless things when statting files.
+        // This isn't important but doesn't hurt.
+        _djstat_flags = _STAT_INODE | _STAT_EXEC_EXT
+                        | _STAT_EXEC_MAGIC | _STAT_DIRSIZE;
+#endif
+
+        return;
+}
+
+
+extern void
+io_no_sparse(void)
+{
+        try_sparse = false;
+        return;
+}
+
+
+/// \brief      Unlink a file
+///
+/// This tries to verify that the file being unlinked really is the file that
+/// we want to unlink by verifying device and inode numbers. There's still
+/// a small unavoidable race, but this is much better than nothing (the file
+/// could have been moved/replaced even hours earlier).
+static void
+io_unlink(const char *name, const struct stat *known_st)
+{
+#if defined(TUKLIB_DOSLIKE)
+        // On DOS-like systems, st_ino is meaningless, so don't bother
+        // testing it. Just silence a compiler warning.
+        (void)known_st;
+#else
+        struct stat new_st;
+
+        // If --force was used, use stat() instead of lstat(). This way
+        // (de)compressing symlinks works correctly. However, it also means
+        // that xz cannot detect if a regular file foo is renamed to bar
+        // and then a symlink foo -> bar is created. Because of stat()
+        // instead of lstat(), xz will think that foo hasn't been replaced
+        // with another file. Thus, xz will remove foo even though it no
+        // longer is the same file that xz used when it started compressing.
+        // Probably it's not too bad though, so this doesn't need a more
+        // complex fix.
+        const int stat_ret = opt_force
+                        ? stat(name, &new_st) : lstat(name, &new_st);
+
+        if (stat_ret
+#       ifdef __VMS
+                        // st_ino is an array, and we don't want to
+                        // compare st_dev at all.
+                        || memcmp(&new_st.st_ino, &known_st->st_ino,
+                                sizeof(new_st.st_ino)) != 0
+#       else
+                        // Typical POSIX-like system
+                        || new_st.st_dev != known_st->st_dev
+                        || new_st.st_ino != known_st->st_ino
+#       endif
+                        )
+                // TRANSLATORS: When compression or decompression finishes,
+                // and xz is going to remove the source file, xz first checks
+                // if the source file still exists, and if it does, does its
+                // device and inode numbers match what xz saw when it opened
+                // the source file. If these checks fail, this message is
+                // shown, %s being the filename, and the file is not deleted.
+                // The check for device and inode numbers is there, because
+                // it is possible that the user has put a new file in place
+                // of the original file, and in that case it obviously
+                // shouldn't be removed.
+                message_error(_("%s: File seems to have been moved, "
+                                "not removing"), name);
+        else
+#endif
+                // There's a race condition between lstat() and unlink()
+                // but at least we have tried to avoid removing wrong file.
+                if (unlink(name))
+                        message_error(_("%s: Cannot remove: %s"),
+                                        name, strerror(errno));
+
+        return;
+}
+
+
+/// \brief      Copies owner/group and permissions
+///
+/// \todo       ACL and EA support
+///
+static void
+io_copy_attrs(const file_pair *pair)
+{
+        // Skip chown and chmod on Windows.
+#ifndef TUKLIB_DOSLIKE
+        // This function is more tricky than you may think at first.
+        // Blindly copying permissions may permit users to access the
+        // destination file who didn't have permission to access the
+        // source file.
+
+        // Try changing the owner of the file. If we aren't root or the owner
+        // isn't already us, fchown() probably doesn't succeed. We warn
+        // about failing fchown() only if we are root.
+        if (fchown(pair->dest_fd, pair->src_st.st_uid, -1) && warn_fchown)
+                message_warning(_("%s: Cannot set the file owner: %s"),
+                                pair->dest_name, strerror(errno));
+
+        mode_t mode;
+
+        if (fchown(pair->dest_fd, -1, pair->src_st.st_gid)) {
+                message_warning(_("%s: Cannot set the file group: %s"),
+                                pair->dest_name, strerror(errno));
+                // We can still safely copy some additional permissions:
+                // `group' must be at least as strict as `other' and
+                // also vice versa.
+                //
+                // NOTE: After this, the owner of the source file may
+                // get additional permissions. This shouldn't be too bad,
+                // because the owner would have had permission to chmod
+                // the original file anyway.
+                mode = ((pair->src_st.st_mode & 0070) >> 3)
+                                & (pair->src_st.st_mode & 0007);
+                mode = (pair->src_st.st_mode & 0700) | (mode << 3) | mode;
+        } else {
+                // Drop the setuid, setgid, and sticky bits.
+                mode = pair->src_st.st_mode & 0777;
+        }
+
+        if (fchmod(pair->dest_fd, mode))
+                message_warning(_("%s: Cannot set the file permissions: %s"),
+                                pair->dest_name, strerror(errno));
+#endif
+
+        // Copy the timestamps. We have several possible ways to do this, of
+        // which some are better in both security and precision.
+        //
+        // First, get the nanosecond part of the timestamps. As of writing,
+        // it's not standardized by POSIX, and there are several names for
+        // the same thing in struct stat.
+        long atime_nsec;
+        long mtime_nsec;
+
+#       if defined(HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC)
+        // GNU and Solaris
+        atime_nsec = pair->src_st.st_atim.tv_nsec;
+        mtime_nsec = pair->src_st.st_mtim.tv_nsec;
+
+#       elif defined(HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC)
+        // BSD
+        atime_nsec = pair->src_st.st_atimespec.tv_nsec;
+        mtime_nsec = pair->src_st.st_mtimespec.tv_nsec;
+
+#       elif defined(HAVE_STRUCT_STAT_ST_ATIMENSEC)
+        // GNU and BSD without extensions
+        atime_nsec = pair->src_st.st_atimensec;
+        mtime_nsec = pair->src_st.st_mtimensec;
+
+#       elif defined(HAVE_STRUCT_STAT_ST_UATIME)
+        // Tru64
+        atime_nsec = pair->src_st.st_uatime * 1000;
+        mtime_nsec = pair->src_st.st_umtime * 1000;
+
+#       elif defined(HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC)
+        // UnixWare
+        atime_nsec = pair->src_st.st_atim.st__tim.tv_nsec;
+        mtime_nsec = pair->src_st.st_mtim.st__tim.tv_nsec;
+
+#       else
+        // Safe fallback
+        atime_nsec = 0;
+        mtime_nsec = 0;
+#       endif
+
+        // Construct a structure to hold the timestamps and call appropriate
+        // function to set the timestamps.
+#if defined(HAVE_FUTIMENS)
+        // Use nanosecond precision.
+        struct timespec tv[2];
+        tv[0].tv_sec = pair->src_st.st_atime;
+        tv[0].tv_nsec = atime_nsec;
+        tv[1].tv_sec = pair->src_st.st_mtime;
+        tv[1].tv_nsec = mtime_nsec;
+
+        (void)futimens(pair->dest_fd, tv);
+
+#elif defined(HAVE_FUTIMES) || defined(HAVE_FUTIMESAT) || defined(HAVE_UTIMES)
+        // Use microsecond precision.
+        struct timeval tv[2];
+        tv[0].tv_sec = pair->src_st.st_atime;
+        tv[0].tv_usec = atime_nsec / 1000;
+        tv[1].tv_sec = pair->src_st.st_mtime;
+        tv[1].tv_usec = mtime_nsec / 1000;
+
+#       if defined(HAVE_FUTIMES)
+        (void)futimes(pair->dest_fd, tv);
+#       elif defined(HAVE_FUTIMESAT)
+        (void)futimesat(pair->dest_fd, NULL, tv);
+#       else
+        // Argh, no function to use a file descriptor to set the timestamp.
+        (void)utimes(pair->dest_name, tv);
+#       endif
+
+#elif defined(HAVE_UTIME)
+        // Use one-second precision. utime() doesn't support using file
+        // descriptor either. Some systems have broken utime() prototype
+        // so don't make this const.
+        struct utimbuf buf = {
+                .actime = pair->src_st.st_atime,
+                .modtime = pair->src_st.st_mtime,
+        };
+
+        // Avoid warnings.
+        (void)atime_nsec;
+        (void)mtime_nsec;
+
+        (void)utime(pair->dest_name, &buf);
+#endif
+
+        return;
+}
+
+
+/// Opens the source file. Returns false on success, true on error.
+static bool
+io_open_src_real(file_pair *pair)
+{
+        // There's nothing to open when reading from stdin.
+        if (pair->src_name == stdin_filename) {
+                pair->src_fd = STDIN_FILENO;
+#ifdef TUKLIB_DOSLIKE
+                setmode(STDIN_FILENO, O_BINARY);
+#endif
+                return false;
+        }
+
+        // Symlinks are not followed unless writing to stdout or --force
+        // was used.
+        const bool follow_symlinks = opt_stdout || opt_force;
+
+        // We accept only regular files if we are writing the output
+        // to disk too. bzip2 allows overriding this with --force but
+        // gzip and xz don't.
+        const bool reg_files_only = !opt_stdout;
+
+        // Flags for open()
+        int flags = O_RDONLY | O_BINARY | O_NOCTTY;
+
+#ifndef TUKLIB_DOSLIKE
+        // If we accept only regular files, we need to be careful to avoid
+        // problems with special files like devices and FIFOs. O_NONBLOCK
+        // prevents blocking when opening such files. When we want to accept
+        // special files, we must not use O_NONBLOCK, or otherwise we won't
+        // block waiting e.g. FIFOs to become readable.
+        if (reg_files_only)
+                flags |= O_NONBLOCK;
+#endif
+
+#if defined(O_NOFOLLOW)
+        if (!follow_symlinks)
+                flags |= O_NOFOLLOW;
+#elif !defined(TUKLIB_DOSLIKE)
+        // Some POSIX-like systems lack O_NOFOLLOW (it's not required
+        // by POSIX). Check for symlinks with a separate lstat() on
+        // these systems.
+        if (!follow_symlinks) {
+                struct stat st;
+                if (lstat(pair->src_name, &st)) {
+                        message_error("%s: %s", pair->src_name,
+                                        strerror(errno));
+                        return true;
+
+                } else if (S_ISLNK(st.st_mode)) {
+                        message_warning(_("%s: Is a symbolic link, "
+                                        "skipping"), pair->src_name);
+                        return true;
+                }
+        }
+#else
+        // Avoid warnings.
+        (void)follow_symlinks;
+#endif
+
+        // Try to open the file. If we are accepting non-regular files,
+        // unblock the caught signals so that open() can be interrupted
+        // if it blocks e.g. due to a FIFO file.
+        if (!reg_files_only)
+                signals_unblock();
+
+        // Maybe this wouldn't need a loop, since all the signal handlers for
+        // which we don't use SA_RESTART set user_abort to true. But it
+        // doesn't hurt to have it just in case.
+        do {
+                pair->src_fd = open(pair->src_name, flags);
+        } while (pair->src_fd == -1 && errno == EINTR && !user_abort);
+
+        if (!reg_files_only)
+                signals_block();
+
+        if (pair->src_fd == -1) {
+                // If we were interrupted, don't display any error message.
+                if (errno == EINTR) {
+                        // All the signals that don't have SA_RESTART
+                        // set user_abort.
+                        assert(user_abort);
+                        return true;
+                }
+
+#ifdef O_NOFOLLOW
+                // Give an understandable error message in if reason
+                // for failing was that the file was a symbolic link.
+                //
+                // Note that at least Linux, OpenBSD, Solaris, and Darwin
+                // use ELOOP to indicate if O_NOFOLLOW was the reason
+                // that open() failed. Because there may be
+                // directories in the pathname, ELOOP may occur also
+                // because of a symlink loop in the directory part.
+                // So ELOOP doesn't tell us what actually went wrong.
+                //
+                // FreeBSD associates EMLINK with O_NOFOLLOW and
+                // Tru64 uses ENOTSUP. We use these directly here
+                // and skip the lstat() call and the associated race.
+                // I want to hear if there are other kernels that
+                // fail with something else than ELOOP with O_NOFOLLOW.
+                bool was_symlink = false;
+
+#       if defined(__FreeBSD__) || defined(__DragonFly__)
+                if (errno == EMLINK)
+                        was_symlink = true;
+
+#       elif defined(__digital__) && defined(__unix__)
+                if (errno == ENOTSUP)
+                        was_symlink = true;
+
+#       elif defined(__NetBSD__)
+                // FIXME? As of 2008-11-20, NetBSD doesn't document what
+                // errno is used with O_NOFOLLOW. It seems to be EFTYPE,
+                // but since it isn't documented, it may be wrong to rely
+                // on it here.
+                if (errno == EFTYPE)
+                        was_symlink = true;
+
+#       else
+                if (errno == ELOOP && !follow_symlinks) {
+                        const int saved_errno = errno;
+                        struct stat st;
+                        if (lstat(pair->src_name, &st) == 0
+                                        && S_ISLNK(st.st_mode))
+                                was_symlink = true;
+
+                        errno = saved_errno;
+                }
+#       endif
+
+                if (was_symlink)
+                        message_warning(_("%s: Is a symbolic link, "
+                                        "skipping"), pair->src_name);
+                else
+#endif
+                        // Something else than O_NOFOLLOW failing
+                        // (assuming that the race conditions didn't
+                        // confuse us).
+                        message_error("%s: %s", pair->src_name,
+                                        strerror(errno));
+
+                return true;
+        }
+
+#ifndef TUKLIB_DOSLIKE
+        // Drop O_NONBLOCK, which is used only when we are accepting only
+        // regular files. After the open() call, we want things to block
+        // instead of giving EAGAIN.
+        if (reg_files_only) {
+                flags = fcntl(pair->src_fd, F_GETFL);
+                if (flags == -1)
+                        goto error_msg;
+
+                flags &= ~O_NONBLOCK;
+
+                if (fcntl(pair->src_fd, F_SETFL, flags))
+                        goto error_msg;
+        }
+#endif
+
+        // Stat the source file. We need the result also when we copy
+        // the permissions, and when unlinking.
+        if (fstat(pair->src_fd, &pair->src_st))
+                goto error_msg;
+
+        if (S_ISDIR(pair->src_st.st_mode)) {
+                message_warning(_("%s: Is a directory, skipping"),
+                                pair->src_name);
+                goto error;
+        }
+
+        if (reg_files_only) {
+                if (!S_ISREG(pair->src_st.st_mode)) {
+                        message_warning(_("%s: Not a regular file, "
+                                        "skipping"), pair->src_name);
+                        goto error;
+                }
+
+                // These are meaningless on Windows.
+#ifndef TUKLIB_DOSLIKE
+                if (pair->src_st.st_mode & (S_ISUID | S_ISGID)) {
+                        // gzip rejects setuid and setgid files even
+                        // when --force was used. bzip2 doesn't check
+                        // for them, but calls fchown() after fchmod(),
+                        // and many systems automatically drop setuid
+                        // and setgid bits there.
+                        //
+                        // We accept setuid and setgid files if
+                        // --force was used. We drop these bits
+                        // explicitly in io_copy_attr().
+                        message_warning(_("%s: File has setuid or "
+                                        "setgid bit set, skipping"),
+                                        pair->src_name);
+                        goto error;
+                }
+
+                if (pair->src_st.st_mode & S_ISVTX) {
+                        message_warning(_("%s: File has sticky bit "
+                                        "set, skipping"),
+                                        pair->src_name);
+                        goto error;
+                }
+
+                if (pair->src_st.st_nlink > 1) {
+                        message_warning(_("%s: Input file has more "
+                                        "than one hard link, "
+                                        "skipping"), pair->src_name);
+                        goto error;
+                }
+#endif
+        }
+
+        return false;
+
+error_msg:
+        message_error("%s: %s", pair->src_name, strerror(errno));
+error:
+        (void)close(pair->src_fd);
+        return true;
+}
+
+
+extern file_pair *
+io_open_src(const char *src_name)
+{
+        if (is_empty_filename(src_name))
+                return NULL;
+
+        // Since we have only one file open at a time, we can use
+        // a statically allocated structure.
+        static file_pair pair;
+
+        pair = (file_pair){
+                .src_name = src_name,
+                .dest_name = NULL,
+                .src_fd = -1,
+                .dest_fd = -1,
+                .src_eof = false,
+                .dest_try_sparse = false,
+                .dest_pending_sparse = 0,
+        };
+
+        // Block the signals, for which we have a custom signal handler, so
+        // that we don't need to worry about EINTR.
+        signals_block();
+        const bool error = io_open_src_real(&pair);
+        signals_unblock();
+
+        return error ? NULL : &pair;
+}
+
+
+/// \brief      Closes source file of the file_pair structure
+///
+/// \param      pair    File whose src_fd should be closed
+/// \param      success If true, the file will be removed from the disk if
+///                     closing succeeds and --keep hasn't been used.
+static void
+io_close_src(file_pair *pair, bool success)
+{
+        if (pair->src_fd != STDIN_FILENO && pair->src_fd != -1) {
+#ifdef TUKLIB_DOSLIKE
+                (void)close(pair->src_fd);
+#endif
+
+                // If we are going to unlink(), do it before closing the file.
+                // This way there's no risk that someone replaces the file and
+                // happens to get same inode number, which would make us
+                // unlink() wrong file.
+                //
+                // NOTE: DOS-like systems are an exception to this, because
+                // they don't allow unlinking files that are open. *sigh*
+                if (success && !opt_keep_original)
+                        io_unlink(pair->src_name, &pair->src_st);
+
+#ifndef TUKLIB_DOSLIKE
+                (void)close(pair->src_fd);
+#endif
+        }
+
+        return;
+}
+
+
+static bool
+io_open_dest_real(file_pair *pair)
+{
+        if (opt_stdout || pair->src_fd == STDIN_FILENO) {
+                // We don't modify or free() this.
+                pair->dest_name = (char *)"(stdout)";
+                pair->dest_fd = STDOUT_FILENO;
+#ifdef TUKLIB_DOSLIKE
+                setmode(STDOUT_FILENO, O_BINARY);
+#endif
+        } else {
+                pair->dest_name = suffix_get_dest_name(pair->src_name);
+                if (pair->dest_name == NULL)
+                        return true;
+
+                // If --force was used, unlink the target file first.
+                if (opt_force && unlink(pair->dest_name) && errno != ENOENT) {
+                        message_error(_("%s: Cannot remove: %s"),
+                                        pair->dest_name, strerror(errno));
+                        free(pair->dest_name);
+                        return true;
+                }
+
+                // Open the file.
+                const int flags = O_WRONLY | O_BINARY | O_NOCTTY
+                                | O_CREAT | O_EXCL;
+                const mode_t mode = S_IRUSR | S_IWUSR;
+                pair->dest_fd = open(pair->dest_name, flags, mode);
+
+                if (pair->dest_fd == -1) {
+                        message_error("%s: %s", pair->dest_name,
+                                        strerror(errno));
+                        free(pair->dest_name);
+                        return true;
+                }
+        }
+
+        // If this really fails... well, we have a safe fallback.
+        if (fstat(pair->dest_fd, &pair->dest_st)) {
+#if defined(__VMS)
+                pair->dest_st.st_ino[0] = 0;
+                pair->dest_st.st_ino[1] = 0;
+                pair->dest_st.st_ino[2] = 0;
+#elif !defined(TUKLIB_DOSLIKE)
+                pair->dest_st.st_dev = 0;
+                pair->dest_st.st_ino = 0;
+#endif
+#ifndef TUKLIB_DOSLIKE
+        } else if (try_sparse && opt_mode == MODE_DECOMPRESS) {
+                // When writing to standard output, we need to be extra
+                // careful:
+                //  - It may be connected to something else than
+                //    a regular file.
+                //  - We aren't necessarily writing to a new empty file
+                //    or to the end of an existing file.
+                //  - O_APPEND may be active.
+                //
+                // TODO: I'm keeping this disabled for DOS-like systems
+                // for now. FAT doesn't support sparse files, but NTFS
+                // does, so maybe this should be enabled on Windows after
+                // some testing.
+                if (pair->dest_fd == STDOUT_FILENO) {
+                        if (!S_ISREG(pair->dest_st.st_mode))
+                                return false;
+
+                        const int flags = fcntl(STDOUT_FILENO, F_GETFL);
+                        if (flags == -1)
+                                return false;
+
+                        if (flags & O_APPEND) {
+                                // Creating a sparse file is not possible
+                                // when O_APPEND is active (it's used by
+                                // shell's >> redirection). As I understand
+                                // it, it is safe to temporarily disable
+                                // O_APPEND in xz, because if someone
+                                // happened to write to the same file at the
+                                // same time, results would be bad anyway
+                                // (users shouldn't assume that xz uses any
+                                // specific block size when writing data).
+                                //
+                                // The write position may be something else
+                                // than the end of the file, so we must fix
+                                // it to start writing at the end of the file
+                                // to imitate O_APPEND.
+                                if (lseek(STDOUT_FILENO, 0, SEEK_END) == -1)
+                                        return false;
+
+                                if (fcntl(STDOUT_FILENO, F_SETFL,
+                                                stdout_flags & ~O_APPEND))
+                                        return false;
+
+                                // Remember the flags so that io_close_dest()
+                                // can restore them.
+                                stdout_flags = flags;
+
+                        } else if (lseek(STDOUT_FILENO, 0, SEEK_CUR)
+                                        != pair->dest_st.st_size) {
+                                // Writing won't start exactly at the end
+                                // of the file. We cannot use sparse output,
+                                // because it would probably corrupt the file.
+                                return false;
+                        }
+                }
+
+                pair->dest_try_sparse = true;
+#endif
+        }
+
+        return false;
+}
+
+
+extern bool
+io_open_dest(file_pair *pair)
+{
+        signals_block();
+        const bool ret = io_open_dest_real(pair);
+        signals_unblock();
+        return ret;
+}
+
+
+/// \brief      Closes destination file of the file_pair structure
+///
+/// \param      pair    File whose dest_fd should be closed
+/// \param      success If false, the file will be removed from the disk.
+///
+/// \return     Zero if closing succeeds. On error, -1 is returned and
+///             error message printed.
+static bool
+io_close_dest(file_pair *pair, bool success)
+{
+#ifndef TUKLIB_DOSLIKE
+        // If io_open_dest() has disabled O_APPEND, restore it here.
+        if (stdout_flags != 0) {
+                assert(pair->dest_fd == STDOUT_FILENO);
+
+                const int fail = fcntl(STDOUT_FILENO, F_SETFL, stdout_flags);
+                stdout_flags = 0;
+
+                if (fail) {
+                        message_error(_("Error restoring the O_APPEND flag "
+                                        "to standard output: %s"),
+                                        strerror(errno));
+                        return true;
+                }
+        }
+#endif
+
+        if (pair->dest_fd == -1 || pair->dest_fd == STDOUT_FILENO)
+                return false;
+
+        if (close(pair->dest_fd)) {
+                message_error(_("%s: Closing the file failed: %s"),
+                                pair->dest_name, strerror(errno));
+
+                // Closing destination file failed, so we cannot trust its
+                // contents. Get rid of junk:
+                io_unlink(pair->dest_name, &pair->dest_st);
+                free(pair->dest_name);
+                return true;
+        }
+
+        // If the operation using this file wasn't successful, we git rid
+        // of the junk file.
+        if (!success)
+                io_unlink(pair->dest_name, &pair->dest_st);
+
+        free(pair->dest_name);
+
+        return false;
+}
+
+
+extern void
+io_close(file_pair *pair, bool success)
+{
+        // Take care of sparseness at the end of the output file.
+        if (success && pair->dest_try_sparse
+                        && pair->dest_pending_sparse > 0) {
+                // Seek forward one byte less than the size of the pending
+                // hole, then write one zero-byte. This way the file grows
+                // to its correct size. An alternative would be to use
+                // ftruncate() but that isn't portable enough (e.g. it
+                // doesn't work with FAT on Linux; FAT isn't that important
+                // since it doesn't support sparse files anyway, but we don't
+                // want to create corrupt files on it).
+                if (lseek(pair->dest_fd, pair->dest_pending_sparse - 1,
+                                SEEK_CUR) == -1) {
+                        message_error(_("%s: Seeking failed when trying "
+                                        "to create a sparse file: %s"),
+                                        pair->dest_name, strerror(errno));
+                        success = false;
+                } else {
+                        const uint8_t zero[1] = { '\0' };
+                        if (io_write_buf(pair, zero, 1))
+                                success = false;
+                }
+        }
+
+        signals_block();
+
+        // Copy the file attributes. We need to skip this if destination
+        // file isn't open or it is standard output.
+        if (success && pair->dest_fd != -1 && pair->dest_fd != STDOUT_FILENO)
+                io_copy_attrs(pair);
+
+        // Close the destination first. If it fails, we must not remove
+        // the source file!
+        if (io_close_dest(pair, success))
+                success = false;
+
+        // Close the source file, and unlink it if the operation using this
+        // file pair was successful and we haven't requested to keep the
+        // source file.
+        io_close_src(pair, success);
+
+        signals_unblock();
+
+        return;
+}
+
+
+extern size_t
+io_read(file_pair *pair, io_buf *buf_union, size_t size)
+{
+        // We use small buffers here.
+        assert(size < SSIZE_MAX);
+
+        uint8_t *buf = buf_union->u8;
+        size_t left = size;
+
+        while (left > 0) {
+                const ssize_t amount = read(pair->src_fd, buf, left);
+
+                if (amount == 0) {
+                        pair->src_eof = true;
+                        break;
+                }
+
+                if (amount == -1) {
+                        if (errno == EINTR) {
+                                if (user_abort)
+                                        return SIZE_MAX;
+
+                                continue;
+                        }
+
+                        message_error(_("%s: Read error: %s"),
+                                        pair->src_name, strerror(errno));
+
+                        // FIXME Is this needed?
+                        pair->src_eof = true;
+
+                        return SIZE_MAX;
+                }
+
+                buf += (size_t)(amount);
+                left -= (size_t)(amount);
+        }
+
+        return size - left;
+}
+
+
+extern bool
+io_pread(file_pair *pair, io_buf *buf, size_t size, off_t pos)
+{
+        // Using lseek() and read() is more portable than pread() and
+        // for us it is as good as real pread().
+        if (lseek(pair->src_fd, pos, SEEK_SET) != pos) {
+                message_error(_("%s: Error seeking the file: %s"),
+                                pair->src_name, strerror(errno));
+                return true;
+        }
+
+        const size_t amount = io_read(pair, buf, size);
+        if (amount == SIZE_MAX)
+                return true;
+
+        if (amount != size) {
+                message_error(_("%s: Unexpected end of file"),
+                                pair->src_name);
+                return true;
+        }
+
+        return false;
+}
+
+
+static bool
+is_sparse(const io_buf *buf)
+{
+        assert(IO_BUFFER_SIZE % sizeof(uint64_t) == 0);
+
+        for (size_t i = 0; i < ARRAY_SIZE(buf->u64); ++i)
+                if (buf->u64[i] != 0)
+                        return false;
+
+        return true;
+}
+
+
+static bool
+io_write_buf(file_pair *pair, const uint8_t *buf, size_t size)
+{
+        assert(size < SSIZE_MAX);
+
+        while (size > 0) {
+                const ssize_t amount = write(pair->dest_fd, buf, size);
+                if (amount == -1) {
+                        if (errno == EINTR) {
+                                if (user_abort)
+                                        return -1;
+
+                                continue;
+                        }
+
+                        // Handle broken pipe specially. gzip and bzip2
+                        // don't print anything on SIGPIPE. In addition,
+                        // gzip --quiet uses exit status 2 (warning) on
+                        // broken pipe instead of whatever raise(SIGPIPE)
+                        // would make it return. It is there to hide "Broken
+                        // pipe" message on some old shells (probably old
+                        // GNU bash).
+                        //
+                        // We don't do anything special with --quiet, which
+                        // is what bzip2 does too. If we get SIGPIPE, we
+                        // will handle it like other signals by setting
+                        // user_abort, and get EPIPE here.
+                        if (errno != EPIPE)
+                                message_error(_("%s: Write error: %s"),
+                                        pair->dest_name, strerror(errno));
+
+                        return true;
+                }
+
+                buf += (size_t)(amount);
+                size -= (size_t)(amount);
+        }
+
+        return false;
+}
+
+
+extern bool
+io_write(file_pair *pair, const io_buf *buf, size_t size)
+{
+        assert(size <= IO_BUFFER_SIZE);
+
+        if (pair->dest_try_sparse) {
+                // Check if the block is sparse (contains only zeros). If it
+                // sparse, we just store the amount and return. We will take
+                // care of actually skipping over the hole when we hit the
+                // next data block or close the file.
+                //
+                // Since io_close() requires that dest_pending_sparse > 0
+                // if the file ends with sparse block, we must also return
+                // if size == 0 to avoid doing the lseek().
+                if (size == IO_BUFFER_SIZE) {
+                        if (is_sparse(buf)) {
+                                pair->dest_pending_sparse += size;
+                                return false;
+                        }
+                } else if (size == 0) {
+                        return false;
+                }
+
+                // This is not a sparse block. If we have a pending hole,
+                // skip it now.
+                if (pair->dest_pending_sparse > 0) {
+                        if (lseek(pair->dest_fd, pair->dest_pending_sparse,
+                                        SEEK_CUR) == -1) {
+                                message_error(_("%s: Seeking failed when "
+                                                "trying to create a sparse "
+                                                "file: %s"), pair->dest_name,
+                                                strerror(errno));
+                                return true;
+                        }
+
+                        pair->dest_pending_sparse = 0;
+                }
+        }
+
+        return io_write_buf(pair, buf->u8, size);
+}