GUI: Fix Tomato RAF theme for all builds. Compilation typo.

[tomato.git] / release / src-rt-6.x.4708 / tools / misc / 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 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 if the reason
                // for failing was that the file was a symbolic link.
                //
                // Note that at least Linux, OpenBSD, Solaris, and Darwin
                // use ELOOP to indicate that 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,
                // and this stupidity went into POSIX-1.2008 too.
                //
                // 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__)
                // As of 2010-09-05, NetBSD doesn't document what errno is
                // used with O_NOFOLLOW. It is EFTYPE though, and I
                // understood that is very unlikely to change even though
                // it is undocumented.
                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 && !S_ISREG(pair->src_st.st_mode)) {
                message_warning(_("%s: Not a regular file, skipping"),
                                pair->src_name);
                goto error;
        }

#ifndef TUKLIB_DOSLIKE
        if (reg_files_only && !opt_force) {
                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);
}