pg_basebackup.c

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/*-------------------------------------------------------------------------
 *
 * pg_basebackup.c - receive a base backup using streaming replication protocol
 *
 * Author: Magnus Hagander <magnus@hagander.net>
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/bin/pg_basebackup/pg_basebackup.c
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <signal.h>
#include <time.h>
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#ifdef HAVE_LIBZ
#include <zlib.h>
#endif

#include "access/xlog_internal.h"
#include "common/file_perm.h"
#include "common/file_utils.h"
#include "common/logging.h"
#include "common/string.h"
#include "fe_utils/recovery_gen.h"
#include "fe_utils/string_utils.h"
#include "getopt_long.h"
#include "libpq-fe.h"
#include "pgtar.h"
#include "pgtime.h"
#include "pqexpbuffer.h"
#include "receivelog.h"
#include "replication/basebackup.h"
#include "streamutil.h"

#define ERRCODE_DATA_CORRUPTED  "XX001"

typedef struct TablespaceListCell
{
    struct TablespaceListCell *next;
    char        old_dir[MAXPGPATH];
    char        new_dir[MAXPGPATH];
} TablespaceListCell;

typedef struct TablespaceList
{
    TablespaceListCell *head;
    TablespaceListCell *tail;
} TablespaceList;

typedef struct WriteTarState
{
    int         tablespacenum;
    char        filename[MAXPGPATH];
    FILE       *tarfile;
    char        tarhdr[512];
    bool        basetablespace;
    bool        in_tarhdr;
    bool        skip_file;
    bool        is_recovery_guc_supported;
    bool        is_postgresql_auto_conf;
    bool        found_postgresql_auto_conf;
    int         file_padding_len;
    size_t      tarhdrsz;
    pgoff_t     filesz;
#ifdef HAVE_LIBZ
    gzFile      ztarfile;
#endif
} WriteTarState;

typedef struct UnpackTarState
{
    int         tablespacenum;
    char        current_path[MAXPGPATH];
    char        filename[MAXPGPATH];
    const char *mapped_tblspc_path;
    pgoff_t     current_len_left;
    int         current_padding;
    FILE       *file;
} UnpackTarState;

typedef struct WriteManifestState
{
    char        filename[MAXPGPATH];
    FILE       *file;
} WriteManifestState;

typedef void (*WriteDataCallback) (size_t nbytes, char *buf,
                                   void *callback_data);

/*
 * pg_xlog has been renamed to pg_wal in version 10.  This version number
 * should be compared with PQserverVersion().
 */
#define MINIMUM_VERSION_FOR_PG_WAL  100000

/*
 * Temporary replication slots are supported from version 10.
 */
#define MINIMUM_VERSION_FOR_TEMP_SLOTS 100000

/*
 * Different ways to include WAL
 */
typedef enum
{
    NO_WAL,
    FETCH_WAL,
    STREAM_WAL
} IncludeWal;

/* Global options */
static char *basedir = NULL;
static TablespaceList tablespace_dirs = {NULL, NULL};
static char *xlog_dir = NULL;
static char format = 'p';       /* p(lain)/t(ar) */
static char *label = "pg_basebackup base backup";
static bool noclean = false;
static bool checksum_failure = false;
static bool showprogress = false;
static bool estimatesize = true;
static int  verbose = 0;
static int  compresslevel = 0;
static IncludeWal includewal = STREAM_WAL;
static bool fastcheckpoint = false;
static bool writerecoveryconf = false;
static bool do_sync = true;
static int  standby_message_timeout = 10 * 1000;    /* 10 sec = default */
static pg_time_t last_progress_report = 0;
static int32 maxrate = 0;       /* no limit by default */
static char *replication_slot = NULL;
static bool temp_replication_slot = true;
static bool create_slot = false;
static bool no_slot = false;
static bool verify_checksums = true;
static bool manifest = true;
static bool manifest_force_encode = false;
static char *manifest_checksums = NULL;

static bool success = false;
static bool made_new_pgdata = false;
static bool found_existing_pgdata = false;
static bool made_new_xlogdir = false;
static bool found_existing_xlogdir = false;
static bool made_tablespace_dirs = false;
static bool found_tablespace_dirs = false;

/* Progress counters */
static uint64 totalsize_kb;
static uint64 totaldone;
static int  tablespacecount;

/* Pipe to communicate with background wal receiver process */
#ifndef WIN32
static int  bgpipe[2] = {-1, -1};
#endif

/* Handle to child process */
static pid_t bgchild = -1;
static bool in_log_streamer = false;

/* End position for xlog streaming, empty string if unknown yet */
static XLogRecPtr xlogendptr;

#ifndef WIN32
static int  has_xlogendptr = 0;
#else
static volatile LONG has_xlogendptr = 0;
#endif

/* Contents of configuration file to be generated */
static PQExpBuffer recoveryconfcontents = NULL;

/* Function headers */
static void usage(void);
static void verify_dir_is_empty_or_create(char *dirname, bool *created, bool *found);
static void progress_report(int tablespacenum, const char *filename, bool force);

static void ReceiveTarFile(PGconn *conn, PGresult *res, int rownum);
static void ReceiveTarCopyChunk(size_t r, char *copybuf, void *callback_data);
static void ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum);
static void ReceiveTarAndUnpackCopyChunk(size_t r, char *copybuf,
                                         void *callback_data);
static void ReceiveBackupManifest(PGconn *conn);
static void ReceiveBackupManifestChunk(size_t r, char *copybuf,
                                       void *callback_data);
static void ReceiveBackupManifestInMemory(PGconn *conn, PQExpBuffer buf);
static void ReceiveBackupManifestInMemoryChunk(size_t r, char *copybuf,
                                               void *callback_data);
static void BaseBackup(void);

static bool reached_end_position(XLogRecPtr segendpos, uint32 timeline,
                                 bool segment_finished);

static const char *get_tablespace_mapping(const char *dir);
static void tablespace_list_append(const char *arg);


static void
cleanup_directories_atexit(void)
{
    if (success || in_log_streamer)
        return;

    if (!noclean && !checksum_failure)
    {
        if (made_new_pgdata)
        {
            pg_log_info("removing data directory \"%s\"", basedir);
            if (!rmtree(basedir, true))
                pg_log_error("failed to remove data directory");
        }
        else if (found_existing_pgdata)
        {
            pg_log_info("removing contents of data directory \"%s\"", basedir);
            if (!rmtree(basedir, false))
                pg_log_error("failed to remove contents of data directory");
        }

        if (made_new_xlogdir)
        {
            pg_log_info("removing WAL directory \"%s\"", xlog_dir);
            if (!rmtree(xlog_dir, true))
                pg_log_error("failed to remove WAL directory");
        }
        else if (found_existing_xlogdir)
        {
            pg_log_info("removing contents of WAL directory \"%s\"", xlog_dir);
            if (!rmtree(xlog_dir, false))
                pg_log_error("failed to remove contents of WAL directory");
        }
    }
    else
    {
        if ((made_new_pgdata || found_existing_pgdata) && !checksum_failure)
            pg_log_info("data directory \"%s\" not removed at user's request", basedir);

        if (made_new_xlogdir || found_existing_xlogdir)
            pg_log_info("WAL directory \"%s\" not removed at user's request", xlog_dir);
    }

    if ((made_tablespace_dirs || found_tablespace_dirs) && !checksum_failure)
        pg_log_info("changes to tablespace directories will not be undone");
}

static void
disconnect_atexit(void)
{
    if (conn != NULL)
        PQfinish(conn);
}

#ifndef WIN32
/*
 * On windows, our background thread dies along with the process. But on
 * Unix, if we have started a subprocess, we want to kill it off so it
 * doesn't remain running trying to stream data.
 */
static void
kill_bgchild_atexit(void)
{
    if (bgchild > 0)
        kill(bgchild, SIGTERM);
}
#endif

/*
 * Split argument into old_dir and new_dir and append to tablespace mapping
 * list.
 */
static void
tablespace_list_append(const char *arg)
{
    TablespaceListCell *cell = (TablespaceListCell *) pg_malloc0(sizeof(TablespaceListCell));
    char       *dst;
    char       *dst_ptr;
    const char *arg_ptr;

    dst_ptr = dst = cell->old_dir;
    for (arg_ptr = arg; *arg_ptr; arg_ptr++)
    {
        if (dst_ptr - dst >= MAXPGPATH)
        {
            pg_log_error("directory name too long");
            exit(1);
        }

        if (*arg_ptr == '\\' && *(arg_ptr + 1) == '=')
            ;                   /* skip backslash escaping = */
        else if (*arg_ptr == '=' && (arg_ptr == arg || *(arg_ptr - 1) != '\\'))
        {
            if (*cell->new_dir)
            {
                pg_log_error("multiple \"=\" signs in tablespace mapping");
                exit(1);
            }
            else
                dst = dst_ptr = cell->new_dir;
        }
        else
            *dst_ptr++ = *arg_ptr;
    }

    if (!*cell->old_dir || !*cell->new_dir)
    {
        pg_log_error("invalid tablespace mapping format \"%s\", must be \"OLDDIR=NEWDIR\"", arg);
        exit(1);
    }

    /*
     * This check isn't absolutely necessary.  But all tablespaces are created
     * with absolute directories, so specifying a non-absolute path here would
     * just never match, possibly confusing users.  It's also good to be
     * consistent with the new_dir check.
     */
    if (!is_absolute_path(cell->old_dir))
    {
        pg_log_error("old directory is not an absolute path in tablespace mapping: %s",
                     cell->old_dir);
        exit(1);
    }

    if (!is_absolute_path(cell->new_dir))
    {
        pg_log_error("new directory is not an absolute path in tablespace mapping: %s",
                     cell->new_dir);
        exit(1);
    }

    /*
     * Comparisons done with these values should involve similarly
     * canonicalized path values.  This is particularly sensitive on Windows
     * where path values may not necessarily use Unix slashes.
     */
    canonicalize_path(cell->old_dir);
    canonicalize_path(cell->new_dir);

    if (tablespace_dirs.tail)
        tablespace_dirs.tail->next = cell;
    else
        tablespace_dirs.head = cell;
    tablespace_dirs.tail = cell;
}


#ifdef HAVE_LIBZ
static const char *
get_gz_error(gzFile gzf)
{
    int         errnum;
    const char *errmsg;

    errmsg = gzerror(gzf, &errnum);
    if (errnum == Z_ERRNO)
        return strerror(errno);
    else
        return errmsg;
}
#endif

static void
usage(void)
{
    printf(_("%s takes a base backup of a running PostgreSQL server.\n\n"),
           progname);
    printf(_("Usage:\n"));
    printf(_("  %s [OPTION]...\n"), progname);
    printf(_("\nOptions controlling the output:\n"));
    printf(_("  -D, --pgdata=DIRECTORY receive base backup into directory\n"));
    printf(_("  -F, --format=p|t       output format (plain (default), tar)\n"));
    printf(_("  -r, --max-rate=RATE    maximum transfer rate to transfer data directory\n"
             "                         (in kB/s, or use suffix \"k\" or \"M\")\n"));
    printf(_("  -R, --write-recovery-conf\n"
             "                         write configuration for replication\n"));
    printf(_("  -T, --tablespace-mapping=OLDDIR=NEWDIR\n"
             "                         relocate tablespace in OLDDIR to NEWDIR\n"));
    printf(_("      --waldir=WALDIR    location for the write-ahead log directory\n"));
    printf(_("  -X, --wal-method=none|fetch|stream\n"
             "                         include required WAL files with specified method\n"));
    printf(_("  -z, --gzip             compress tar output\n"));
    printf(_("  -Z, --compress=0-9     compress tar output with given compression level\n"));
    printf(_("\nGeneral options:\n"));
    printf(_("  -c, --checkpoint=fast|spread\n"
             "                         set fast or spread checkpointing\n"));
    printf(_("  -C, --create-slot      create replication slot\n"));
    printf(_("  -l, --label=LABEL      set backup label\n"));
    printf(_("  -n, --no-clean         do not clean up after errors\n"));
    printf(_("  -N, --no-sync          do not wait for changes to be written safely to disk\n"));
    printf(_("  -P, --progress         show progress information\n"));
    printf(_("  -S, --slot=SLOTNAME    replication slot to use\n"));
    printf(_("  -v, --verbose          output verbose messages\n"));
    printf(_("  -V, --version          output version information, then exit\n"));
    printf(_("      --no-slot          prevent creation of temporary replication slot\n"));
    printf(_("      --no-verify-checksums\n"
             "                         do not verify checksums\n"));
    printf(_("      --no-estimate-size do not estimate backup size in server side\n"));
    printf(_("      --no-manifest      suppress generation of backup manifest\n"));
    printf(_("      --manifest-force-encode\n"
             "                         hex encode all filenames in manifest\n"));
    printf(_("      --manifest-checksums=SHA{224,256,384,512}|CRC32C|NONE\n"
             "                         use algorithm for manifest checksums\n"));
    printf(_("  -?, --help             show this help, then exit\n"));
    printf(_("\nConnection options:\n"));
    printf(_("  -d, --dbname=CONNSTR   connection string\n"));
    printf(_("  -h, --host=HOSTNAME    database server host or socket directory\n"));
    printf(_("  -p, --port=PORT        database server port number\n"));
    printf(_("  -s, --status-interval=INTERVAL\n"
             "                         time between status packets sent to server (in seconds)\n"));
    printf(_("  -U, --username=NAME    connect as specified database user\n"));
    printf(_("  -w, --no-password      never prompt for password\n"));
    printf(_("  -W, --password         force password prompt (should happen automatically)\n"));
    printf(_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
    printf(_("%s home page: <%s>\n"), PACKAGE_NAME, PACKAGE_URL);
}


/*
 * Called in the background process every time data is received.
 * On Unix, we check to see if there is any data on our pipe
 * (which would mean we have a stop position), and if it is, check if
 * it is time to stop.
 * On Windows, we are in a single process, so we can just check if it's
 * time to stop.
 */
static bool
reached_end_position(XLogRecPtr segendpos, uint32 timeline,
                     bool segment_finished)
{
    if (!has_xlogendptr)
    {
#ifndef WIN32
        fd_set      fds;
        struct timeval tv;
        int         r;

        /*
         * Don't have the end pointer yet - check our pipe to see if it has
         * been sent yet.
         */
        FD_ZERO(&fds);
        FD_SET(bgpipe[0], &fds);

        MemSet(&tv, 0, sizeof(tv));

        r = select(bgpipe[0] + 1, &fds, NULL, NULL, &tv);
        if (r == 1)
        {
            char        xlogend[64];
            uint32      hi,
                        lo;

            MemSet(xlogend, 0, sizeof(xlogend));
            r = read(bgpipe[0], xlogend, sizeof(xlogend) - 1);
            if (r < 0)
            {
                pg_log_error("could not read from ready pipe: %m");
                exit(1);
            }

            if (sscanf(xlogend, "%X/%X", &hi, &lo) != 2)
            {
                pg_log_error("could not parse write-ahead log location \"%s\"",
                             xlogend);
                exit(1);
            }
            xlogendptr = ((uint64) hi) << 32 | lo;
            has_xlogendptr = 1;

            /*
             * Fall through to check if we've reached the point further
             * already.
             */
        }
        else
        {
            /*
             * No data received on the pipe means we don't know the end
             * position yet - so just say it's not time to stop yet.
             */
            return false;
        }
#else

        /*
         * On win32, has_xlogendptr is set by the main thread, so if it's not
         * set here, we just go back and wait until it shows up.
         */
        return false;
#endif
    }

    /*
     * At this point we have an end pointer, so compare it to the current
     * position to figure out if it's time to stop.
     */
    if (segendpos >= xlogendptr)
        return true;

    /*
     * Have end pointer, but haven't reached it yet - so tell the caller to
     * keep streaming.
     */
    return false;
}

typedef struct
{
    PGconn     *bgconn;
    XLogRecPtr  startptr;
    char        xlog[MAXPGPATH];    /* directory or tarfile depending on mode */
    char       *sysidentifier;
    int         timeline;
} logstreamer_param;

static int
LogStreamerMain(logstreamer_param *param)
{
    StreamCtl   stream;

    in_log_streamer = true;

    MemSet(&stream, 0, sizeof(stream));
    stream.startpos = param->startptr;
    stream.timeline = param->timeline;
    stream.sysidentifier = param->sysidentifier;
    stream.stream_stop = reached_end_position;
#ifndef WIN32
    stream.stop_socket = bgpipe[0];
#else
    stream.stop_socket = PGINVALID_SOCKET;
#endif
    stream.standby_message_timeout = standby_message_timeout;
    stream.synchronous = false;
    /* fsync happens at the end of pg_basebackup for all data */
    stream.do_sync = false;
    stream.mark_done = true;
    stream.partial_suffix = NULL;
    stream.replication_slot = replication_slot;

    if (format == 'p')
        stream.walmethod = CreateWalDirectoryMethod(param->xlog, 0,
                                                    stream.do_sync);
    else
        stream.walmethod = CreateWalTarMethod(param->xlog, compresslevel,
                                              stream.do_sync);

    if (!ReceiveXlogStream(param->bgconn, &stream))

        /*
         * Any errors will already have been reported in the function process,
         * but we need to tell the parent that we didn't shutdown in a nice
         * way.
         */
        return 1;

    if (!stream.walmethod->finish())
    {
        pg_log_error("could not finish writing WAL files: %m");
        return 1;
    }

    PQfinish(param->bgconn);

    if (format == 'p')
        FreeWalDirectoryMethod();
    else
        FreeWalTarMethod();
    pg_free(stream.walmethod);

    return 0;
}

/*
 * Initiate background process for receiving xlog during the backup.
 * The background stream will use its own database connection so we can
 * stream the logfile in parallel with the backups.
 */
static void
StartLogStreamer(char *startpos, uint32 timeline, char *sysidentifier)
{
    logstreamer_param *param;
    uint32      hi,
                lo;
    char        statusdir[MAXPGPATH];

    param = pg_malloc0(sizeof(logstreamer_param));
    param->timeline = timeline;
    param->sysidentifier = sysidentifier;

    /* Convert the starting position */
    if (sscanf(startpos, "%X/%X", &hi, &lo) != 2)
    {
        pg_log_error("could not parse write-ahead log location \"%s\"",
                     startpos);
        exit(1);
    }
    param->startptr = ((uint64) hi) << 32 | lo;
    /* Round off to even segment position */
    param->startptr -= XLogSegmentOffset(param->startptr, WalSegSz);

#ifndef WIN32
    /* Create our background pipe */
    if (pipe(bgpipe) < 0)
    {
        pg_log_error("could not create pipe for background process: %m");
        exit(1);
    }
#endif

    /* Get a second connection */
    param->bgconn = GetConnection();
    if (!param->bgconn)
        /* Error message already written in GetConnection() */
        exit(1);

    /* In post-10 cluster, pg_xlog has been renamed to pg_wal */
    snprintf(param->xlog, sizeof(param->xlog), "%s/%s",
             basedir,
             PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
             "pg_xlog" : "pg_wal");

    /* Temporary replication slots are only supported in 10 and newer */
    if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_TEMP_SLOTS)
        temp_replication_slot = false;

    /*
     * Create replication slot if requested
     */
    if (temp_replication_slot && !replication_slot)
        replication_slot = psprintf("pg_basebackup_%d", (int) PQbackendPID(param->bgconn));
    if (temp_replication_slot || create_slot)
    {
        if (!CreateReplicationSlot(param->bgconn, replication_slot, NULL,
                                   temp_replication_slot, true, true, false))
            exit(1);

        if (verbose)
        {
            if (temp_replication_slot)
                pg_log_info("created temporary replication slot \"%s\"",
                            replication_slot);
            else
                pg_log_info("created replication slot \"%s\"",
                            replication_slot);
        }
    }

    if (format == 'p')
    {
        /*
         * Create pg_wal/archive_status or pg_xlog/archive_status (and thus
         * pg_wal or pg_xlog) depending on the target server so we can write
         * to basedir/pg_wal or basedir/pg_xlog as the directory entry in the
         * tar file may arrive later.
         */
        snprintf(statusdir, sizeof(statusdir), "%s/%s/archive_status",
                 basedir,
                 PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
                 "pg_xlog" : "pg_wal");

        if (pg_mkdir_p(statusdir, pg_dir_create_mode) != 0 && errno != EEXIST)
        {
            pg_log_error("could not create directory \"%s\": %m", statusdir);
            exit(1);
        }
    }

    /*
     * Start a child process and tell it to start streaming. On Unix, this is
     * a fork(). On Windows, we create a thread.
     */
#ifndef WIN32
    bgchild = fork();
    if (bgchild == 0)
    {
        /* in child process */
        exit(LogStreamerMain(param));
    }
    else if (bgchild < 0)
    {
        pg_log_error("could not create background process: %m");
        exit(1);
    }

    /*
     * Else we are in the parent process and all is well.
     */
    atexit(kill_bgchild_atexit);
#else                           /* WIN32 */
    bgchild = _beginthreadex(NULL, 0, (void *) LogStreamerMain, param, 0, NULL);
    if (bgchild == 0)
    {
        pg_log_error("could not create background thread: %m");
        exit(1);
    }
#endif
}

/*
 * Verify that the given directory exists and is empty. If it does not
 * exist, it is created. If it exists but is not empty, an error will
 * be given and the process ended.
 */
static void
verify_dir_is_empty_or_create(char *dirname, bool *created, bool *found)
{
    switch (pg_check_dir(dirname))
    {
        case 0:

            /*
             * Does not exist, so create
             */
            if (pg_mkdir_p(dirname, pg_dir_create_mode) == -1)
            {
                pg_log_error("could not create directory \"%s\": %m", dirname);
                exit(1);
            }
            if (created)
                *created = true;
            return;
        case 1:

            /*
             * Exists, empty
             */
            if (found)
                *found = true;
            return;
        case 2:
        case 3:
        case 4:

            /*
             * Exists, not empty
             */
            pg_log_error("directory \"%s\" exists but is not empty", dirname);
            exit(1);
        case -1:

            /*
             * Access problem
             */
            pg_log_error("could not access directory \"%s\": %m", dirname);
            exit(1);
    }
}


/*
 * Print a progress report based on the global variables. If verbose output
 * is enabled, also print the current file name.
 *
 * Progress report is written at maximum once per second, unless the
 * force parameter is set to true.
 */
static void
progress_report(int tablespacenum, const char *filename, bool force)
{
    int         percent;
    char        totaldone_str[32];
    char        totalsize_str[32];
    pg_time_t   now;

    if (!showprogress)
        return;

    now = time(NULL);
    if (now == last_progress_report && !force)
        return;                 /* Max once per second */

    last_progress_report = now;
    percent = totalsize_kb ? (int) ((totaldone / 1024) * 100 / totalsize_kb) : 0;

    /*
     * Avoid overflowing past 100% or the full size. This may make the total
     * size number change as we approach the end of the backup (the estimate
     * will always be wrong if WAL is included), but that's better than having
     * the done column be bigger than the total.
     */
    if (percent > 100)
        percent = 100;
    if (totaldone / 1024 > totalsize_kb)
        totalsize_kb = totaldone / 1024;

    /*
     * Separate step to keep platform-dependent format code out of
     * translatable strings.  And we only test for INT64_FORMAT availability
     * in snprintf, not fprintf.
     */
    snprintf(totaldone_str, sizeof(totaldone_str), INT64_FORMAT,
             totaldone / 1024);
    snprintf(totalsize_str, sizeof(totalsize_str), INT64_FORMAT, totalsize_kb);

#define VERBOSE_FILENAME_LENGTH 35
    if (verbose)
    {
        if (!filename)

            /*
             * No filename given, so clear the status line (used for last
             * call)
             */
            fprintf(stderr,
                    ngettext("%*s/%s kB (100%%), %d/%d tablespace %*s",
                             "%*s/%s kB (100%%), %d/%d tablespaces %*s",
                             tablespacecount),
                    (int) strlen(totalsize_str),
                    totaldone_str, totalsize_str,
                    tablespacenum, tablespacecount,
                    VERBOSE_FILENAME_LENGTH + 5, "");
        else
        {
            bool        truncate = (strlen(filename) > VERBOSE_FILENAME_LENGTH);

            fprintf(stderr,
                    ngettext("%*s/%s kB (%d%%), %d/%d tablespace (%s%-*.*s)",
                             "%*s/%s kB (%d%%), %d/%d tablespaces (%s%-*.*s)",
                             tablespacecount),
                    (int) strlen(totalsize_str),
                    totaldone_str, totalsize_str, percent,
                    tablespacenum, tablespacecount,
            /* Prefix with "..." if we do leading truncation */
                    truncate ? "..." : "",
                    truncate ? VERBOSE_FILENAME_LENGTH - 3 : VERBOSE_FILENAME_LENGTH,
                    truncate ? VERBOSE_FILENAME_LENGTH - 3 : VERBOSE_FILENAME_LENGTH,
            /* Truncate filename at beginning if it's too long */
                    truncate ? filename + strlen(filename) - VERBOSE_FILENAME_LENGTH + 3 : filename);
        }
    }
    else
        fprintf(stderr,
                ngettext("%*s/%s kB (%d%%), %d/%d tablespace",
                         "%*s/%s kB (%d%%), %d/%d tablespaces",
                         tablespacecount),
                (int) strlen(totalsize_str),
                totaldone_str, totalsize_str, percent,
                tablespacenum, tablespacecount);

    if (isatty(fileno(stderr)))
        fprintf(stderr, "\r");
    else
        fprintf(stderr, "\n");
}

static int32
parse_max_rate(char *src)
{
    double      result;
    char       *after_num;
    char       *suffix = NULL;

    errno = 0;
    result = strtod(src, &after_num);
    if (src == after_num)
    {
        pg_log_error("transfer rate \"%s\" is not a valid value", src);
        exit(1);
    }
    if (errno != 0)
    {
        pg_log_error("invalid transfer rate \"%s\": %m", src);
        exit(1);
    }

    if (result <= 0)
    {
        /*
         * Reject obviously wrong values here.
         */
        pg_log_error("transfer rate must be greater than zero");
        exit(1);
    }

    /*
     * Evaluate suffix, after skipping over possible whitespace. Lack of
     * suffix means kilobytes.
     */
    while (*after_num != '\0' && isspace((unsigned char) *after_num))
        after_num++;

    if (*after_num != '\0')
    {
        suffix = after_num;
        if (*after_num == 'k')
        {
            /* kilobyte is the expected unit. */
            after_num++;
        }
        else if (*after_num == 'M')
        {
            after_num++;
            result *= 1024.0;
        }
    }

    /* The rest can only consist of white space. */
    while (*after_num != '\0' && isspace((unsigned char) *after_num))
        after_num++;

    if (*after_num != '\0')
    {
        pg_log_error("invalid --max-rate unit: \"%s\"", suffix);
        exit(1);
    }

    /* Valid integer? */
    if ((uint64) result != (uint64) ((uint32) result))
    {
        pg_log_error("transfer rate \"%s\" exceeds integer range", src);
        exit(1);
    }

    /*
     * The range is checked on the server side too, but avoid the server
     * connection if a nonsensical value was passed.
     */
    if (result < MAX_RATE_LOWER || result > MAX_RATE_UPPER)
    {
        pg_log_error("transfer rate \"%s\" is out of range", src);
        exit(1);
    }

    return (int32) result;
}

/*
 * Read a stream of COPY data and invoke the provided callback for each
 * chunk.
 */
static void
ReceiveCopyData(PGconn *conn, WriteDataCallback callback,
                void *callback_data)
{
    PGresult   *res;

    /* Get the COPY data stream. */
    res = PQgetResult(conn);
    if (PQresultStatus(res) != PGRES_COPY_OUT)
    {
        pg_log_error("could not get COPY data stream: %s",
                     PQerrorMessage(conn));
        exit(1);
    }
    PQclear(res);

    /* Loop over chunks until done. */
    while (1)
    {
        int         r;
        char       *copybuf;

        r = PQgetCopyData(conn, &copybuf, 0);
        if (r == -1)
        {
            /* End of chunk. */
            break;
        }
        else if (r == -2)
        {
            pg_log_error("could not read COPY data: %s",
                         PQerrorMessage(conn));
            exit(1);
        }

        (*callback) (r, copybuf, callback_data);

        PQfreemem(copybuf);
    }
}

/*
 * Write a piece of tar data
 */
static void
writeTarData(WriteTarState *state, char *buf, int r)
{
#ifdef HAVE_LIBZ
    if (state->ztarfile != NULL)
    {
        if (gzwrite(state->ztarfile, buf, r) != r)
        {
            pg_log_error("could not write to compressed file \"%s\": %s",
                         state->filename, get_gz_error(state->ztarfile));
            exit(1);
        }
    }
    else
#endif
    {
        if (fwrite(buf, r, 1, state->tarfile) != 1)
        {
            pg_log_error("could not write to file \"%s\": %m",
                         state->filename);
            exit(1);
        }
    }
}

/*
 * Receive a tar format file from the connection to the server, and write
 * the data from this file directly into a tar file. If compression is
 * enabled, the data will be compressed while written to the file.
 *
 * The file will be named base.tar[.gz] if it's for the main data directory
 * or <tablespaceoid>.tar[.gz] if it's for another tablespace.
 *
 * No attempt to inspect or validate the contents of the file is done.
 */
static void
ReceiveTarFile(PGconn *conn, PGresult *res, int rownum)
{
    char        zerobuf[1024];
    WriteTarState state;

    memset(&state, 0, sizeof(state));
    state.tablespacenum = rownum;
    state.basetablespace = PQgetisnull(res, rownum, 0);
    state.in_tarhdr = true;

    /* recovery.conf is integrated into postgresql.conf in 12 and newer */
    if (PQserverVersion(conn) >= MINIMUM_VERSION_FOR_RECOVERY_GUC)
        state.is_recovery_guc_supported = true;

    if (state.basetablespace)
    {
        /*
         * Base tablespaces
         */
        if (strcmp(basedir, "-") == 0)
        {
#ifdef WIN32
            _setmode(fileno(stdout), _O_BINARY);
#endif

#ifdef HAVE_LIBZ
            if (compresslevel != 0)
            {
                int     fd = dup(fileno(stdout));
                if (fd < 0)
                {
                    pg_log_error("could not duplicate stdout: %m");
                    exit(1);
                }

                state.ztarfile = gzdopen(fd, "wb");
                if (state.ztarfile == NULL)
                {
                    pg_log_error("could not open output file: %m");
                    exit(1);
                }

                if (gzsetparams(state.ztarfile, compresslevel,
                                Z_DEFAULT_STRATEGY) != Z_OK)
                {
                    pg_log_error("could not set compression level %d: %s",
                                 compresslevel, get_gz_error(state.ztarfile));
                    exit(1);
                }
            }
            else
#endif
                state.tarfile = stdout;
            strcpy(state.filename, "-");
        }
        else
        {
#ifdef HAVE_LIBZ
            if (compresslevel != 0)
            {
                snprintf(state.filename, sizeof(state.filename),
                         "%s/base.tar.gz", basedir);
                state.ztarfile = gzopen(state.filename, "wb");
                if (gzsetparams(state.ztarfile, compresslevel,
                                Z_DEFAULT_STRATEGY) != Z_OK)
                {
                    pg_log_error("could not set compression level %d: %s",
                                 compresslevel, get_gz_error(state.ztarfile));
                    exit(1);
                }
            }
            else
#endif
            {
                snprintf(state.filename, sizeof(state.filename),
                         "%s/base.tar", basedir);
                state.tarfile = fopen(state.filename, "wb");
            }
        }
    }
    else
    {
        /*
         * Specific tablespace
         */
#ifdef HAVE_LIBZ
        if (compresslevel != 0)
        {
            snprintf(state.filename, sizeof(state.filename),
                     "%s/%s.tar.gz",
                     basedir, PQgetvalue(res, rownum, 0));
            state.ztarfile = gzopen(state.filename, "wb");
            if (gzsetparams(state.ztarfile, compresslevel,
                            Z_DEFAULT_STRATEGY) != Z_OK)
            {
                pg_log_error("could not set compression level %d: %s",
                             compresslevel, get_gz_error(state.ztarfile));
                exit(1);
            }
        }
        else
#endif
        {
            snprintf(state.filename, sizeof(state.filename), "%s/%s.tar",
                     basedir, PQgetvalue(res, rownum, 0));
            state.tarfile = fopen(state.filename, "wb");
        }
    }

#ifdef HAVE_LIBZ
    if (compresslevel != 0)
    {
        if (!state.ztarfile)
        {
            /* Compression is in use */
            pg_log_error("could not create compressed file \"%s\": %s",
                         state.filename, get_gz_error(state.ztarfile));
            exit(1);
        }
    }
    else
#endif
    {
        /* Either no zlib support, or zlib support but compresslevel = 0 */
        if (!state.tarfile)
        {
            pg_log_error("could not create file \"%s\": %m", state.filename);
            exit(1);
        }
    }

    ReceiveCopyData(conn, ReceiveTarCopyChunk, &state);

    /*
     * End of copy data. If requested, and this is the base tablespace, write
     * configuration file into the tarfile. When done, close the file (but not
     * stdout).
     *
     * Also, write two completely empty blocks at the end of the tar file, as
     * required by some tar programs.
     */

    MemSet(zerobuf, 0, sizeof(zerobuf));

    if (state.basetablespace && writerecoveryconf)
    {
        char        header[512];

        /*
         * If postgresql.auto.conf has not been found in the streamed data,
         * add recovery configuration to postgresql.auto.conf if recovery
         * parameters are GUCs.  If the instance connected to is older than
         * 12, create recovery.conf with this data otherwise.
         */
        if (!state.found_postgresql_auto_conf || !state.is_recovery_guc_supported)
        {
            int         padding;

            tarCreateHeader(header,
                            state.is_recovery_guc_supported ? "postgresql.auto.conf" : "recovery.conf",
                            NULL,
                            recoveryconfcontents->len,
                            pg_file_create_mode, 04000, 02000,
                            time(NULL));

            padding = ((recoveryconfcontents->len + 511) & ~511) - recoveryconfcontents->len;

            writeTarData(&state, header, sizeof(header));
            writeTarData(&state, recoveryconfcontents->data,
                         recoveryconfcontents->len);
            if (padding)
                writeTarData(&state, zerobuf, padding);
        }

        /*
         * standby.signal is supported only if recovery parameters are GUCs.
         */
        if (state.is_recovery_guc_supported)
        {
            tarCreateHeader(header, "standby.signal", NULL,
                            0,  /* zero-length file */
                            pg_file_create_mode, 04000, 02000,
                            time(NULL));

            writeTarData(&state, header, sizeof(header));
            writeTarData(&state, zerobuf, 511);
        }
    }

    /*
     * Normally, we emit the backup manifest as a separate file, but when
     * we're writing a tarfile to stdout, we don't have that option, so
     * include it in the one tarfile we've got.
     */
    if (strcmp(basedir, "-") == 0)
    {
        char        header[512];
        PQExpBufferData buf;

        initPQExpBuffer(&buf);
        ReceiveBackupManifestInMemory(conn, &buf);
        if (PQExpBufferDataBroken(buf))
        {
            pg_log_error("out of memory");
            exit(1);
        }
        tarCreateHeader(header, "backup_manifest", NULL, buf.len,
                        pg_file_create_mode, 04000, 02000,
                        time(NULL));
        writeTarData(&state, header, sizeof(header));
        writeTarData(&state, buf.data, buf.len);
        termPQExpBuffer(&buf);
    }

    /* 2 * 512 bytes empty data at end of file */
    writeTarData(&state, zerobuf, sizeof(zerobuf));

#ifdef HAVE_LIBZ
    if (state.ztarfile != NULL)
    {
        if (gzclose(state.ztarfile) != 0)
        {
            pg_log_error("could not close compressed file \"%s\": %s",
                         state.filename, get_gz_error(state.ztarfile));
            exit(1);
        }
    }
    else
#endif
    {
        if (strcmp(basedir, "-") != 0)
        {
            if (fclose(state.tarfile) != 0)
            {
                pg_log_error("could not close file \"%s\": %m",
                             state.filename);
                exit(1);
            }
        }
    }

    progress_report(rownum, state.filename, true);

    /*
     * Do not sync the resulting tar file yet, all files are synced once at
     * the end.
     */
}

/*
 * Receive one chunk of tar-format data from the server.
 */
static void
ReceiveTarCopyChunk(size_t r, char *copybuf, void *callback_data)
{
    WriteTarState *state = callback_data;

    if (!writerecoveryconf || !state->basetablespace)
    {
        /*
         * When not writing config file, or when not working on the base
         * tablespace, we never have to look for an existing configuration
         * file in the stream.
         */
        writeTarData(state, copybuf, r);
    }
    else
    {
        /*
         * Look for a config file in the existing tar stream. If it's there,
         * we must skip it so we can later overwrite it with our own version
         * of the file.
         *
         * To do this, we have to process the individual files inside the TAR
         * stream. The stream consists of a header and zero or more chunks,
         * all 512 bytes long. The stream from the server is broken up into
         * smaller pieces, so we have to track the size of the files to find
         * the next header structure.
         */
        int         rr = r;
        int         pos = 0;

        while (rr > 0)
        {
            if (state->in_tarhdr)
            {
                /*
                 * We're currently reading a header structure inside the TAR
                 * stream, i.e. the file metadata.
                 */
                if (state->tarhdrsz < 512)
                {
                    /*
                     * Copy the header structure into tarhdr in case the
                     * header is not aligned to 512 bytes or it's not returned
                     * in whole by the last PQgetCopyData call.
                     */
                    int         hdrleft;
                    int         bytes2copy;

                    hdrleft = 512 - state->tarhdrsz;
                    bytes2copy = (rr > hdrleft ? hdrleft : rr);

                    memcpy(&state->tarhdr[state->tarhdrsz], copybuf + pos,
                           bytes2copy);

                    rr -= bytes2copy;
                    pos += bytes2copy;
                    state->tarhdrsz += bytes2copy;
                }
                else
                {
                    /*
                     * We have the complete header structure in tarhdr, look
                     * at the file metadata: we may want append recovery info
                     * into postgresql.auto.conf and skip standby.signal file
                     * if recovery parameters are integrated as GUCs, and
                     * recovery.conf otherwise. In both cases we must
                     * calculate tar padding.
                     */
                    if (state->is_recovery_guc_supported)
                    {
                        state->skip_file =
                            (strcmp(&state->tarhdr[0], "standby.signal") == 0);
                        state->is_postgresql_auto_conf =
                            (strcmp(&state->tarhdr[0], "postgresql.auto.conf") == 0);
                    }
                    else
                        state->skip_file =
                            (strcmp(&state->tarhdr[0], "recovery.conf") == 0);

                    state->filesz = read_tar_number(&state->tarhdr[124], 12);
                    state->file_padding_len =
                        ((state->filesz + 511) & ~511) - state->filesz;

                    if (state->is_recovery_guc_supported &&
                        state->is_postgresql_auto_conf &&
                        writerecoveryconf)
                    {
                        /* replace tar header */
                        char        header[512];

                        tarCreateHeader(header, "postgresql.auto.conf", NULL,
                                        state->filesz + recoveryconfcontents->len,
                                        pg_file_create_mode, 04000, 02000,
                                        time(NULL));

                        writeTarData(state, header, sizeof(header));
                    }
                    else
                    {
                        /* copy stream with padding */
                        state->filesz += state->file_padding_len;

                        if (!state->skip_file)
                        {
                            /*
                             * If we're not skipping the file, write the tar
                             * header unmodified.
                             */
                            writeTarData(state, state->tarhdr, 512);
                        }
                    }

                    /* Next part is the file, not the header */
                    state->in_tarhdr = false;
                }
            }
            else
            {
                /*
                 * We're processing a file's contents.
                 */
                if (state->filesz > 0)
                {
                    /*
                     * We still have data to read (and possibly write).
                     */
                    int         bytes2write;

                    bytes2write = (state->filesz > rr ? rr : state->filesz);

                    if (!state->skip_file)
                        writeTarData(state, copybuf + pos, bytes2write);

                    rr -= bytes2write;
                    pos += bytes2write;
                    state->filesz -= bytes2write;
                }
                else if (state->is_recovery_guc_supported &&
                         state->is_postgresql_auto_conf &&
                         writerecoveryconf)
                {
                    /* append recovery config to postgresql.auto.conf */
                    int         padding;
                    int         tailsize;

                    tailsize = (512 - state->file_padding_len) + recoveryconfcontents->len;
                    padding = ((tailsize + 511) & ~511) - tailsize;

                    writeTarData(state, recoveryconfcontents->data,
                                 recoveryconfcontents->len);

                    if (padding)
                    {
                        char        zerobuf[512];

                        MemSet(zerobuf, 0, sizeof(zerobuf));
                        writeTarData(state, zerobuf, padding);
                    }

                    /* skip original file padding */
                    state->is_postgresql_auto_conf = false;
                    state->skip_file = true;
                    state->filesz += state->file_padding_len;

                    state->found_postgresql_auto_conf = true;
                }
                else
                {
                    /*
                     * No more data in the current file, the next piece of
                     * data (if any) will be a new file header structure.
                     */
                    state->in_tarhdr = true;
                    state->skip_file = false;
                    state->is_postgresql_auto_conf = false;
                    state->tarhdrsz = 0;
                    state->filesz = 0;
                }
            }
        }
    }
    totaldone += r;
    progress_report(state->tablespacenum, state->filename, false);
}


/*
 * Retrieve tablespace path, either relocated or original depending on whether
 * -T was passed or not.
 */
static const char *
get_tablespace_mapping(const char *dir)
{
    TablespaceListCell *cell;
    char        canon_dir[MAXPGPATH];

    /* Canonicalize path for comparison consistency */
    strlcpy(canon_dir, dir, sizeof(canon_dir));
    canonicalize_path(canon_dir);

    for (cell = tablespace_dirs.head; cell; cell = cell->next)
        if (strcmp(canon_dir, cell->old_dir) == 0)
            return cell->new_dir;

    return dir;
}


/*
 * Receive a tar format stream from the connection to the server, and unpack
 * the contents of it into a directory. Only files, directories and
 * symlinks are supported, no other kinds of special files.
 *
 * If the data is for the main data directory, it will be restored in the
 * specified directory. If it's for another tablespace, it will be restored
 * in the original or mapped directory.
 */
static void
ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum)
{
    UnpackTarState state;
    bool        basetablespace;

    memset(&state, 0, sizeof(state));
    state.tablespacenum = rownum;

    basetablespace = PQgetisnull(res, rownum, 0);
    if (basetablespace)
        strlcpy(state.current_path, basedir, sizeof(state.current_path));
    else
        strlcpy(state.current_path,
                get_tablespace_mapping(PQgetvalue(res, rownum, 1)),
                sizeof(state.current_path));

    ReceiveCopyData(conn, ReceiveTarAndUnpackCopyChunk, &state);


    if (state.file)
        fclose(state.file);

    progress_report(rownum, state.filename, true);

    if (state.file != NULL)
    {
        pg_log_error("COPY stream ended before last file was finished");
        exit(1);
    }

    if (basetablespace && writerecoveryconf)
        WriteRecoveryConfig(conn, basedir, recoveryconfcontents);

    /*
     * No data is synced here, everything is done for all tablespaces at the
     * end.
     */
}

static void
ReceiveTarAndUnpackCopyChunk(size_t r, char *copybuf, void *callback_data)
{
    UnpackTarState *state = callback_data;

    if (state->file == NULL)
    {
#ifndef WIN32
        int         filemode;
#endif

        /*
         * No current file, so this must be the header for a new file
         */
        if (r != 512)
        {
            pg_log_error("invalid tar block header size: %zu", r);
            exit(1);
        }
        totaldone += 512;

        state->current_len_left = read_tar_number(&copybuf[124], 12);

#ifndef WIN32
        /* Set permissions on the file */
        filemode = read_tar_number(&copybuf[100], 8);
#endif

        /*
         * All files are padded up to 512 bytes
         */
        state->current_padding =
            ((state->current_len_left + 511) & ~511) - state->current_len_left;

        /*
         * First part of header is zero terminated filename
         */
        snprintf(state->filename, sizeof(state->filename),
                 "%s/%s", state->current_path, copybuf);
        if (state->filename[strlen(state->filename) - 1] == '/')
        {
            /*
             * Ends in a slash means directory or symlink to directory
             */
            if (copybuf[156] == '5')
            {
                /*
                 * Directory. Remove trailing slash first.
                 */
                state->filename[strlen(state->filename) - 1] = '\0';
                if (mkdir(state->filename, pg_dir_create_mode) != 0)
                {
                    /*
                     * When streaming WAL, pg_wal (or pg_xlog for pre-9.6
                     * clusters) will have been created by the wal receiver
                     * process. Also, when the WAL directory location was
                     * specified, pg_wal (or pg_xlog) has already been created
                     * as a symbolic link before starting the actual backup.
                     * So just ignore creation failures on related
                     * directories.
                     */
                    if (!((pg_str_endswith(state->filename, "/pg_wal") ||
                           pg_str_endswith(state->filename, "/pg_xlog") ||
                           pg_str_endswith(state->filename, "/archive_status")) &&
                          errno == EEXIST))
                    {
                        pg_log_error("could not create directory \"%s\": %m",
                                     state->filename);
                        exit(1);
                    }
                }
#ifndef WIN32
                if (chmod(state->filename, (mode_t) filemode))
                    pg_log_error("could not set permissions on directory \"%s\": %m",
                                 state->filename);
#endif
            }
            else if (copybuf[156] == '2')
            {
                /*
                 * Symbolic link
                 *
                 * It's most likely a link in pg_tblspc directory, to the
                 * location of a tablespace. Apply any tablespace mapping
                 * given on the command line (--tablespace-mapping). (We
                 * blindly apply the mapping without checking that the link
                 * really is inside pg_tblspc. We don't expect there to be
                 * other symlinks in a data directory, but if there are, you
                 * can call it an undocumented feature that you can map them
                 * too.)
                 */
                state->filename[strlen(state->filename) - 1] = '\0';    /* Remove trailing slash */

                state->mapped_tblspc_path =
                    get_tablespace_mapping(&copybuf[157]);
                if (symlink(state->mapped_tblspc_path, state->filename) != 0)
                {
                    pg_log_error("could not create symbolic link from \"%s\" to \"%s\": %m",
                                 state->filename, state->mapped_tblspc_path);
                    exit(1);
                }
            }
            else
            {
                pg_log_error("unrecognized link indicator \"%c\"",
                             copybuf[156]);
                exit(1);
            }
            return;             /* directory or link handled */
        }

        /*
         * regular file
         */
        state->file = fopen(state->filename, "wb");
        if (!state->file)
        {
            pg_log_error("could not create file \"%s\": %m", state->filename);
            exit(1);
        }

#ifndef WIN32
        if (chmod(state->filename, (mode_t) filemode))
            pg_log_error("could not set permissions on file \"%s\": %m",
                         state->filename);
#endif

        if (state->current_len_left == 0)
        {
            /*
             * Done with this file, next one will be a new tar header
             */
            fclose(state->file);
            state->file = NULL;
            return;
        }
    }                           /* new file */
    else
    {
        /*
         * Continuing blocks in existing file
         */
        if (state->current_len_left == 0 && r == state->current_padding)
        {
            /*
             * Received the padding block for this file, ignore it and close
             * the file, then move on to the next tar header.
             */
            fclose(state->file);
            state->file = NULL;
            totaldone += r;
            return;
        }

        if (fwrite(copybuf, r, 1, state->file) != 1)
        {
            pg_log_error("could not write to file \"%s\": %m", state->filename);
            exit(1);
        }
        totaldone += r;
        progress_report(state->tablespacenum, state->filename, false);

        state->current_len_left -= r;
        if (state->current_len_left == 0 && state->current_padding == 0)
        {
            /*
             * Received the last block, and there is no padding to be
             * expected. Close the file and move on to the next tar header.
             */
            fclose(state->file);
            state->file = NULL;
            return;
        }
    }                           /* continuing data in existing file */
}

/*
 * Receive the backup manifest file and write it out to a file.
 */
static void
ReceiveBackupManifest(PGconn *conn)
{
    WriteManifestState state;

    snprintf(state.filename, sizeof(state.filename),
             "%s/backup_manifest.tmp", basedir);
    state.file = fopen(state.filename, "wb");
    if (state.file == NULL)
    {
        pg_log_error("could not create file \"%s\": %m", state.filename);
        exit(1);
    }

    ReceiveCopyData(conn, ReceiveBackupManifestChunk, &state);

    fclose(state.file);
}

/*
 * Receive one chunk of the backup manifest file and write it out to a file.
 */
static void
ReceiveBackupManifestChunk(size_t r, char *copybuf, void *callback_data)
{
    WriteManifestState *state = callback_data;

    if (fwrite(copybuf, r, 1, state->file) != 1)
    {
        pg_log_error("could not write to file \"%s\": %m", state->filename);
        exit(1);
    }
}

/*
 * Receive the backup manifest file and write it out to a file.
 */
static void
ReceiveBackupManifestInMemory(PGconn *conn, PQExpBuffer buf)
{
    ReceiveCopyData(conn, ReceiveBackupManifestInMemoryChunk, buf);
}

/*
 * Receive one chunk of the backup manifest file and write it out to a file.
 */
static void
ReceiveBackupManifestInMemoryChunk(size_t r, char *copybuf,
                                   void *callback_data)
{
    PQExpBuffer buf = callback_data;

    appendPQExpBuffer(buf, copybuf, r);
}

static void
BaseBackup(void)
{
    PGresult   *res;
    char       *sysidentifier;
    TimeLineID  latesttli;
    TimeLineID  starttli;
    char       *basebkp;
    char        escaped_label[MAXPGPATH];
    char       *maxrate_clause = NULL;
    char       *manifest_clause;
    char       *manifest_checksums_clause = "";
    int         i;
    char        xlogstart[64];
    char        xlogend[64];
    int         minServerMajor,
                maxServerMajor;
    int         serverVersion,
                serverMajor;
    int         writing_to_stdout;

    Assert(conn != NULL);

    /*
     * Check server version. BASE_BACKUP command was introduced in 9.1, so we
     * can't work with servers older than 9.1.
     */
    minServerMajor = 901;
    maxServerMajor = PG_VERSION_NUM / 100;
    serverVersion = PQserverVersion(conn);
    serverMajor = serverVersion / 100;
    if (serverMajor < minServerMajor || serverMajor > maxServerMajor)
    {
        const char *serverver = PQparameterStatus(conn, "server_version");

        pg_log_error("incompatible server version %s",
                     serverver ? serverver : "'unknown'");
        exit(1);
    }

    /*
     * If WAL streaming was requested, also check that the server is new
     * enough for that.
     */
    if (includewal == STREAM_WAL && !CheckServerVersionForStreaming(conn))
    {
        /*
         * Error message already written in CheckServerVersionForStreaming(),
         * but add a hint about using -X none.
         */
        pg_log_info("HINT: use -X none or -X fetch to disable log streaming");
        exit(1);
    }

    /*
     * Build contents of configuration file if requested
     */
    if (writerecoveryconf)
        recoveryconfcontents = GenerateRecoveryConfig(conn, replication_slot);

    /*
     * Run IDENTIFY_SYSTEM so we can get the timeline
     */
    if (!RunIdentifySystem(conn, &sysidentifier, &latesttli, NULL, NULL))
        exit(1);

    /*
     * Start the actual backup
     */
    PQescapeStringConn(conn, escaped_label, label, sizeof(escaped_label), &i);

    if (maxrate > 0)
        maxrate_clause = psprintf("MAX_RATE %u", maxrate);

    if (manifest)
    {
        if (serverMajor < 1300)
        {
            const char *serverver = PQparameterStatus(conn, "server_version");

            pg_log_error("backup manifests are not supported by server version %s",
                         serverver ? serverver : "'unknown'");
            exit(1);
        }

        if (manifest_force_encode)
            manifest_clause = "MANIFEST 'force-encode'";
        else
            manifest_clause = "MANIFEST 'yes'";
        if (manifest_checksums != NULL)
            manifest_checksums_clause = psprintf("MANIFEST_CHECKSUMS '%s'",
                                                 manifest_checksums);
    }
    else
    {
        if (serverMajor < 1300)
            manifest_clause = "";
        else
            manifest_clause = "MANIFEST 'no'";
    }

    if (verbose)
        pg_log_info("initiating base backup, waiting for checkpoint to complete");

    if (showprogress && !verbose)
    {
        fprintf(stderr, "waiting for checkpoint");
        if (isatty(fileno(stderr)))
            fprintf(stderr, "\r");
        else
            fprintf(stderr, "\n");
    }

    basebkp =
        psprintf("BASE_BACKUP LABEL '%s' %s %s %s %s %s %s %s %s %s",
                 escaped_label,
                 estimatesize ? "PROGRESS" : "",
                 includewal == FETCH_WAL ? "WAL" : "",
                 fastcheckpoint ? "FAST" : "",
                 includewal == NO_WAL ? "" : "NOWAIT",
                 maxrate_clause ? maxrate_clause : "",
                 format == 't' ? "TABLESPACE_MAP" : "",
                 verify_checksums ? "" : "NOVERIFY_CHECKSUMS",
                 manifest_clause,
                 manifest_checksums_clause);

    if (PQsendQuery(conn, basebkp) == 0)
    {
        pg_log_error("could not send replication command \"%s\": %s",
                     "BASE_BACKUP", PQerrorMessage(conn));
        exit(1);
    }

    /*
     * Get the starting WAL location
     */
    res = PQgetResult(conn);
    if (PQresultStatus(res) != PGRES_TUPLES_OK)
    {
        pg_log_error("could not initiate base backup: %s",
                     PQerrorMessage(conn));
        exit(1);
    }
    if (PQntuples(res) != 1)
    {
        pg_log_error("server returned unexpected response to BASE_BACKUP command; got %d rows and %d fields, expected %d rows and %d fields",
                     PQntuples(res), PQnfields(res), 1, 2);
        exit(1);
    }

    strlcpy(xlogstart, PQgetvalue(res, 0, 0), sizeof(xlogstart));

    if (verbose)
        pg_log_info("checkpoint completed");

    /*
     * 9.3 and later sends the TLI of the starting point. With older servers,
     * assume it's the same as the latest timeline reported by
     * IDENTIFY_SYSTEM.
     */
    if (PQnfields(res) >= 2)
        starttli = atoi(PQgetvalue(res, 0, 1));
    else
        starttli = latesttli;
    PQclear(res);
    MemSet(xlogend, 0, sizeof(xlogend));

    if (verbose && includewal != NO_WAL)
        pg_log_info("write-ahead log start point: %s on timeline %u",
                    xlogstart, starttli);

    /*
     * Get the header
     */
    res = PQgetResult(conn);
    if (PQresultStatus(res) != PGRES_TUPLES_OK)
    {
        pg_log_error("could not get backup header: %s",
                     PQerrorMessage(conn));
        exit(1);
    }
    if (PQntuples(res) < 1)
    {
        pg_log_error("no data returned from server");
        exit(1);
    }

    /*
     * Sum up the total size, for progress reporting
     */
    totalsize_kb = totaldone = 0;
    tablespacecount = PQntuples(res);
    for (i = 0; i < PQntuples(res); i++)
    {
        totalsize_kb += atol(PQgetvalue(res, i, 2));

        /*
         * Verify tablespace directories are empty. Don't bother with the
         * first once since it can be relocated, and it will be checked before
         * we do anything anyway.
         */
        if (format == 'p' && !PQgetisnull(res, i, 1))
        {
            char       *path = unconstify(char *, get_tablespace_mapping(PQgetvalue(res, i, 1)));

            verify_dir_is_empty_or_create(path, &made_tablespace_dirs, &found_tablespace_dirs);
        }
    }

    /*
     * When writing to stdout, require a single tablespace
     */
    writing_to_stdout = format == 't' && strcmp(basedir, "-") == 0;
    if (writing_to_stdout && PQntuples(res) > 1)
    {
        pg_log_error("can only write single tablespace to stdout, database has %d",
                     PQntuples(res));
        exit(1);
    }

    /*
     * If we're streaming WAL, start the streaming session before we start
     * receiving the actual data chunks.
     */
    if (includewal == STREAM_WAL)
    {
        if (verbose)
            pg_log_info("starting background WAL receiver");
        StartLogStreamer(xlogstart, starttli, sysidentifier);
    }

    /*
     * Start receiving chunks
     */
    for (i = 0; i < PQntuples(res); i++)
    {
        if (format == 't')
            ReceiveTarFile(conn, res, i);
        else
            ReceiveAndUnpackTarFile(conn, res, i);
    }                           /* Loop over all tablespaces */

    /*
     * Now receive backup manifest, if appropriate.
     *
     * If we're writing a tarfile to stdout, ReceiveTarFile will have already
     * processed the backup manifest and included it in the output tarfile.
     * Such a configuration doesn't allow for writing multiple files.
     *
     * If we're talking to an older server, it won't send a backup manifest,
     * so don't try to receive one.
     */
    if (!writing_to_stdout && manifest)
        ReceiveBackupManifest(conn);

    if (showprogress)
    {
        progress_report(PQntuples(res), NULL, true);
        if (isatty(fileno(stderr)))
            fprintf(stderr, "\n");  /* Need to move to next line */
    }

    PQclear(res);

    /*
     * Get the stop position
     */
    res = PQgetResult(conn);
    if (PQresultStatus(res) != PGRES_TUPLES_OK)
    {
        pg_log_error("could not get write-ahead log end position from server: %s",
                     PQerrorMessage(conn));
        exit(1);
    }
    if (PQntuples(res) != 1)
    {
        pg_log_error("no write-ahead log end position returned from server");
        exit(1);
    }
    strlcpy(xlogend, PQgetvalue(res, 0, 0), sizeof(xlogend));
    if (verbose && includewal != NO_WAL)
        pg_log_info("write-ahead log end point: %s", xlogend);
    PQclear(res);

    res = PQgetResult(conn);
    if (PQresultStatus(res) != PGRES_COMMAND_OK)
    {
        const char *sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);

        if (sqlstate &&
            strcmp(sqlstate, ERRCODE_DATA_CORRUPTED) == 0)
        {
            pg_log_error("checksum error occurred");
            checksum_failure = true;
        }
        else
        {
            pg_log_error("final receive failed: %s",
                         PQerrorMessage(conn));
        }
        exit(1);
    }

    if (bgchild > 0)
    {
#ifndef WIN32
        int         status;
        pid_t       r;
#else
        DWORD       status;

        /*
         * get a pointer sized version of bgchild to avoid warnings about
         * casting to a different size on WIN64.
         */
        intptr_t    bgchild_handle = bgchild;
        uint32      hi,
                    lo;
#endif

        if (verbose)
            pg_log_info("waiting for background process to finish streaming ...");

#ifndef WIN32
        if (write(bgpipe[1], xlogend, strlen(xlogend)) != strlen(xlogend))
        {
            pg_log_info("could not send command to background pipe: %m");
            exit(1);
        }

        /* Just wait for the background process to exit */
        r = waitpid(bgchild, &status, 0);
        if (r == (pid_t) -1)
        {
            pg_log_error("could not wait for child process: %m");
            exit(1);
        }
        if (r != bgchild)
        {
            pg_log_error("child %d died, expected %d", (int) r, (int) bgchild);
            exit(1);
        }
        if (status != 0)
        {
            pg_log_error("%s", wait_result_to_str(status));
            exit(1);
        }
        /* Exited normally, we're happy! */
#else                           /* WIN32 */

        /*
         * On Windows, since we are in the same process, we can just store the
         * value directly in the variable, and then set the flag that says
         * it's there.
         */
        if (sscanf(xlogend, "%X/%X", &hi, &lo) != 2)
        {
            pg_log_error("could not parse write-ahead log location \"%s\"",
                         xlogend);
            exit(1);
        }
        xlogendptr = ((uint64) hi) << 32 | lo;
        InterlockedIncrement(&has_xlogendptr);

        /* First wait for the thread to exit */
        if (WaitForSingleObjectEx((HANDLE) bgchild_handle, INFINITE, FALSE) !=
            WAIT_OBJECT_0)
        {
            _dosmaperr(GetLastError());
            pg_log_error("could not wait for child thread: %m");
            exit(1);
        }
        if (GetExitCodeThread((HANDLE) bgchild_handle, &status) == 0)
        {
            _dosmaperr(GetLastError());
            pg_log_error("could not get child thread exit status: %m");
            exit(1);
        }
        if (status != 0)
        {
            pg_log_error("child thread exited with error %u",
                         (unsigned int) status);
            exit(1);
        }
        /* Exited normally, we're happy */
#endif
    }

    /* Free the configuration file contents */
    destroyPQExpBuffer(recoveryconfcontents);

    /*
     * End of copy data. Final result is already checked inside the loop.
     */
    PQclear(res);
    PQfinish(conn);
    conn = NULL;

    /*
     * Make data persistent on disk once backup is completed. For tar format
     * sync the parent directory and all its contents as each tar file was not
     * synced after being completed.  In plain format, all the data of the
     * base directory is synced, taking into account all the tablespaces.
     * Errors are not considered fatal.
     */
    if (do_sync)
    {
        if (verbose)
            pg_log_info("syncing data to disk ...");
        if (format == 't')
        {
            if (strcmp(basedir, "-") != 0)
                (void) fsync_dir_recurse(basedir);
        }
        else
        {
            (void) fsync_pgdata(basedir, serverVersion);
        }
    }

    /*
     * After synchronizing data to disk, perform a durable rename of
     * backup_manifest.tmp to backup_manifest, if we wrote such a file. This
     * way, a failure or system crash before we reach this point will leave us
     * without a backup_manifest file, decreasing the chances that a directory
     * we leave behind will be mistaken for a valid backup.
     */
    if (!writing_to_stdout && manifest)
    {
        char        tmp_filename[MAXPGPATH];
        char        filename[MAXPGPATH];

        if (verbose)
            pg_log_info("renaming backup_manifest.tmp to backup_manifest");

        snprintf(tmp_filename, MAXPGPATH, "%s/backup_manifest.tmp", basedir);
        snprintf(filename, MAXPGPATH, "%s/backup_manifest", basedir);

        /* durable_rename emits its own log message in case of failure */
        if (durable_rename(tmp_filename, filename) != 0)
            exit(1);
    }

    if (verbose)
        pg_log_info("base backup completed");
}


int
main(int argc, char **argv)
{
    static struct option long_options[] = {
        {"help", no_argument, NULL, '?'},
        {"version", no_argument, NULL, 'V'},
        {"pgdata", required_argument, NULL, 'D'},
        {"format", required_argument, NULL, 'F'},
        {"checkpoint", required_argument, NULL, 'c'},
        {"create-slot", no_argument, NULL, 'C'},
        {"max-rate", required_argument, NULL, 'r'},
        {"write-recovery-conf", no_argument, NULL, 'R'},
        {"slot", required_argument, NULL, 'S'},
        {"tablespace-mapping", required_argument, NULL, 'T'},
        {"wal-method", required_argument, NULL, 'X'},
        {"gzip", no_argument, NULL, 'z'},
        {"compress", required_argument, NULL, 'Z'},
        {"label", required_argument, NULL, 'l'},
        {"no-clean", no_argument, NULL, 'n'},
        {"no-sync", no_argument, NULL, 'N'},
        {"dbname", required_argument, NULL, 'd'},
        {"host", required_argument, NULL, 'h'},
        {"port", required_argument, NULL, 'p'},
        {"username", required_argument, NULL, 'U'},
        {"no-password", no_argument, NULL, 'w'},
        {"password", no_argument, NULL, 'W'},
        {"status-interval", required_argument, NULL, 's'},
        {"verbose", no_argument, NULL, 'v'},
        {"progress", no_argument, NULL, 'P'},
        {"waldir", required_argument, NULL, 1},
        {"no-slot", no_argument, NULL, 2},
        {"no-verify-checksums", no_argument, NULL, 3},
        {"no-estimate-size", no_argument, NULL, 4},
        {"no-manifest", no_argument, NULL, 5},
        {"manifest-force-encode", no_argument, NULL, 6},
        {"manifest-checksums", required_argument, NULL, 7},
        {NULL, 0, NULL, 0}
    };
    int         c;

    int         option_index;

    pg_logging_init(argv[0]);
    progname = get_progname(argv[0]);
    set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_basebackup"));

    if (argc > 1)
    {
        if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
        {
            usage();
            exit(0);
        }
        else if (strcmp(argv[1], "-V") == 0
                 || strcmp(argv[1], "--version") == 0)
        {
            puts("pg_basebackup (PostgreSQL) " PG_VERSION);
            exit(0);
        }
    }

    atexit(cleanup_directories_atexit);

    while ((c = getopt_long(argc, argv, "CD:F:r:RS:T:X:l:nNzZ:d:c:h:p:U:s:wWkvPm:",
                            long_options, &option_index)) != -1)
    {
        switch (c)
        {
            case 'C':
                create_slot = true;
                break;
            case 'D':
                basedir = pg_strdup(optarg);
                break;
            case 'F':
                if (strcmp(optarg, "p") == 0 || strcmp(optarg, "plain") == 0)
                    format = 'p';
                else if (strcmp(optarg, "t") == 0 || strcmp(optarg, "tar") == 0)
                    format = 't';
                else
                {
                    pg_log_error("invalid output format \"%s\", must be \"plain\" or \"tar\"",
                                 optarg);
                    exit(1);
                }
                break;
            case 'r':
                maxrate = parse_max_rate(optarg);
                break;
            case 'R':
                writerecoveryconf = true;
                break;
            case 'S':

                /*
                 * When specifying replication slot name, use a permanent
                 * slot.
                 */
                replication_slot = pg_strdup(optarg);
                temp_replication_slot = false;
                break;
            case 2:
                no_slot = true;
                break;
            case 'T':
                tablespace_list_append(optarg);
                break;
            case 'X':
                if (strcmp(optarg, "n") == 0 ||
                    strcmp(optarg, "none") == 0)
                {
                    includewal = NO_WAL;
                }
                else if (strcmp(optarg, "f") == 0 ||
                         strcmp(optarg, "fetch") == 0)
                {
                    includewal = FETCH_WAL;
                }
                else if (strcmp(optarg, "s") == 0 ||
                         strcmp(optarg, "stream") == 0)
                {
                    includewal = STREAM_WAL;
                }
                else
                {
                    pg_log_error("invalid wal-method option \"%s\", must be \"fetch\", \"stream\", or \"none\"",
                                 optarg);
                    exit(1);
                }
                break;
            case 1:
                xlog_dir = pg_strdup(optarg);
                break;
            case 'l':
                label = pg_strdup(optarg);
                break;
            case 'n':
                noclean = true;
                break;
            case 'N':
                do_sync = false;
                break;
            case 'z':
#ifdef HAVE_LIBZ
                compresslevel = Z_DEFAULT_COMPRESSION;
#else
                compresslevel = 1;  /* will be rejected below */
#endif
                break;
            case 'Z':
                compresslevel = atoi(optarg);
                if (compresslevel < 0 || compresslevel > 9)
                {
                    pg_log_error("invalid compression level \"%s\"", optarg);
                    exit(1);
                }
                break;
            case 'c':
                if (pg_strcasecmp(optarg, "fast") == 0)
                    fastcheckpoint = true;
                else if (pg_strcasecmp(optarg, "spread") == 0)
                    fastcheckpoint = false;
                else
                {
                    pg_log_error("invalid checkpoint argument \"%s\", must be \"fast\" or \"spread\"",
                                 optarg);
                    exit(1);
                }
                break;
            case 'd':
                connection_string = pg_strdup(optarg);
                break;
            case 'h':
                dbhost = pg_strdup(optarg);
                break;
            case 'p':
                dbport = pg_strdup(optarg);
                break;
            case 'U':
                dbuser = pg_strdup(optarg);
                break;
            case 'w':
                dbgetpassword = -1;
                break;
            case 'W':
                dbgetpassword = 1;
                break;
            case 's':
                standby_message_timeout = atoi(optarg) * 1000;
                if (standby_message_timeout < 0)
                {
                    pg_log_error("invalid status interval \"%s\"", optarg);
                    exit(1);
                }
                break;
            case 'v':
                verbose++;
                break;
            case 'P':
                showprogress = true;
                break;
            case 3:
                verify_checksums = false;
                break;
            case 4:
                estimatesize = false;
                break;
            case 5:
                manifest = false;
                break;
            case 6:
                manifest_force_encode = true;
                break;
            case 7:
                manifest_checksums = pg_strdup(optarg);
                break;
            default:

                /*
                 * getopt_long already emitted a complaint
                 */
                fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                        progname);
                exit(1);
        }
    }

    /*
     * Any non-option arguments?
     */
    if (optind < argc)
    {
        pg_log_error("too many command-line arguments (first is \"%s\")",
                     argv[optind]);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    /*
     * Required arguments
     */
    if (basedir == NULL)
    {
        pg_log_error("no target directory specified");
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    /*
     * Mutually exclusive arguments
     */
    if (format == 'p' && compresslevel != 0)
    {
        pg_log_error("only tar mode backups can be compressed");
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (format == 't' && includewal == STREAM_WAL && strcmp(basedir, "-") == 0)
    {
        pg_log_error("cannot stream write-ahead logs in tar mode to stdout");
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (replication_slot && includewal != STREAM_WAL)
    {
        pg_log_error("replication slots can only be used with WAL streaming");
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (no_slot)
    {
        if (replication_slot)
        {
            pg_log_error("--no-slot cannot be used with slot name");
            fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                    progname);
            exit(1);
        }
        temp_replication_slot = false;
    }

    if (create_slot)
    {
        if (!replication_slot)
        {
            pg_log_error("%s needs a slot to be specified using --slot",
                         "--create-slot");
            fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                    progname);
            exit(1);
        }

        if (no_slot)
        {
            pg_log_error("--create-slot and --no-slot are incompatible options");
            fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                    progname);
            exit(1);
        }
    }

    if (xlog_dir)
    {
        if (format != 'p')
        {
            pg_log_error("WAL directory location can only be specified in plain mode");
            fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                    progname);
            exit(1);
        }

        /* clean up xlog directory name, check it's absolute */
        canonicalize_path(xlog_dir);
        if (!is_absolute_path(xlog_dir))
        {
            pg_log_error("WAL directory location must be an absolute path");
            fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                    progname);
            exit(1);
        }
    }

#ifndef HAVE_LIBZ
    if (compresslevel != 0)
    {
        pg_log_error("this build does not support compression");
        exit(1);
    }
#endif

    if (showprogress && !estimatesize)
    {
        pg_log_error("--progress and --no-estimate-size are incompatible options");
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (!manifest && manifest_checksums != NULL)
    {
        pg_log_error("--no-manifest and --manifest-checksums are incompatible options");
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (!manifest && manifest_force_encode)
    {
        pg_log_error("--no-manifest and --manifest-force-encode are incompatible options");
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    /* connection in replication mode to server */
    conn = GetConnection();
    if (!conn)
    {
        /* Error message already written in GetConnection() */
        exit(1);
    }
    atexit(disconnect_atexit);

    /*
     * Set umask so that directories/files are created with the same
     * permissions as directories/files in the source data directory.
     *
     * pg_mode_mask is set to owner-only by default and then updated in
     * GetConnection() where we get the mode from the server-side with
     * RetrieveDataDirCreatePerm() and then call SetDataDirectoryCreatePerm().
     */
    umask(pg_mode_mask);

    /*
     * Verify that the target directory exists, or create it. For plaintext
     * backups, always require the directory. For tar backups, require it
     * unless we are writing to stdout.
     */
    if (format == 'p' || strcmp(basedir, "-") != 0)
        verify_dir_is_empty_or_create(basedir, &made_new_pgdata, &found_existing_pgdata);

    /* determine remote server's xlog segment size */
    if (!RetrieveWalSegSize(conn))
        exit(1);

    /* Create pg_wal symlink, if required */
    if (xlog_dir)
    {
        char       *linkloc;

        verify_dir_is_empty_or_create(xlog_dir, &made_new_xlogdir, &found_existing_xlogdir);

        /*
         * Form name of the place where the symlink must go. pg_xlog has been
         * renamed to pg_wal in post-10 clusters.
         */
        linkloc = psprintf("%s/%s", basedir,
                           PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
                           "pg_xlog" : "pg_wal");

#ifdef HAVE_SYMLINK
        if (symlink(xlog_dir, linkloc) != 0)
        {
            pg_log_error("could not create symbolic link \"%s\": %m", linkloc);
            exit(1);
        }
#else
        pg_log_error("symlinks are not supported on this platform");
        exit(1);
#endif
        free(linkloc);
    }

    BaseBackup();

    success = true;
    return 0;
}