pg_combinebackup.c

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/*-------------------------------------------------------------------------
 *
 * pg_combinebackup.c
 *      Combine incremental backups with prior backups.
 *
 * Copyright (c) 2017-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/bin/pg_combinebackup/pg_combinebackup.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <dirent.h>
#include <fcntl.h>
#include <limits.h>
 
#ifdef HAVE_COPYFILE_H
#include <copyfile.h>
#endif
#ifdef __linux__
#include <sys/ioctl.h>
#include <linux/fs.h>
#endif
 
#include "access/xlog_internal.h"
#include "backup_label.h"
#include "common/checksum_helper.h"
#include "common/controldata_utils.h"
#include "common/file_perm.h"
#include "common/file_utils.h"
#include "common/logging.h"
#include "common/relpath.h"
#include "copy_file.h"
#include "fe_utils/option_utils.h"
#include "fe_utils/version.h"
#include "getopt_long.h"
#include "lib/stringinfo.h"
#include "load_manifest.h"
#include "reconstruct.h"
#include "write_manifest.h"
 
/* Incremental file naming convention. */
#define INCREMENTAL_PREFIX          "INCREMENTAL."
#define INCREMENTAL_PREFIX_LENGTH   (sizeof(INCREMENTAL_PREFIX) - 1)
 
/*
 * Tracking for directories that need to be removed, or have their contents
 * removed, if the operation fails.
 */
typedef struct cb_cleanup_dir
{
    char       *target_path;
    bool        rmtopdir;
    struct cb_cleanup_dir *next;
} cb_cleanup_dir;
 
/*
 * Stores a tablespace mapping provided using -T, --tablespace-mapping.
 */
typedef struct cb_tablespace_mapping
{
    char        old_dir[MAXPGPATH];
    char        new_dir[MAXPGPATH];
    struct cb_tablespace_mapping *next;
} cb_tablespace_mapping;
 
/*
 * Stores data parsed from all command-line options.
 */
typedef struct cb_options
{
    bool        debug;
    char       *output;
    bool        dry_run;
    bool        no_sync;
    cb_tablespace_mapping *tsmappings;
    pg_checksum_type manifest_checksums;
    bool        no_manifest;
    DataDirSyncMethod sync_method;
    CopyMethod  copy_method;
} cb_options;
 
/*
 * Data about a tablespace.
 *
 * Every normal tablespace needs a tablespace mapping, but in-place tablespaces
 * don't, so the list of tablespaces can contain more entries than the list of
 * tablespace mappings.
 */
typedef struct cb_tablespace
{
    Oid         oid;
    bool        in_place;
    char        old_dir[MAXPGPATH];
    char        new_dir[MAXPGPATH];
    struct cb_tablespace *next;
} cb_tablespace;
 
/* Directories to be removed if we exit uncleanly. */
static cb_cleanup_dir *cleanup_dir_list = NULL;
 
static void add_tablespace_mapping(cb_options *opt, char *arg);
static StringInfo check_backup_label_files(int n_backups, char **backup_dirs);
static uint64 check_control_files(int n_backups, char **backup_dirs);
static void check_input_dir_permissions(char *dir);
static void cleanup_directories_atexit(void);
static void create_output_directory(char *dirname, cb_options *opt);
static void help(const char *progname);
static bool parse_oid(char *s, Oid *result);
static void process_directory_recursively(Oid tsoid,
                                          char *input_directory,
                                          char *output_directory,
                                          char *relative_path,
                                          int n_prior_backups,
                                          char **prior_backup_dirs,
                                          manifest_data **manifests,
                                          manifest_writer *mwriter,
                                          cb_options *opt);
static void remember_to_cleanup_directory(char *target_path, bool rmtopdir);
static void reset_directory_cleanup_list(void);
static cb_tablespace *scan_for_existing_tablespaces(char *pathname,
                                                    cb_options *opt);
static void slurp_file(int fd, char *filename, StringInfo buf, int maxlen);
 
/*
 * Main program.
 */
int
main(int argc, char *argv[])
{
    static struct option long_options[] = {
        {"debug", no_argument, NULL, 'd'},
        {"dry-run", no_argument, NULL, 'n'},
        {"no-sync", no_argument, NULL, 'N'},
        {"output", required_argument, NULL, 'o'},
        {"tablespace-mapping", required_argument, NULL, 'T'},
        {"link", no_argument, NULL, 'k'},
        {"manifest-checksums", required_argument, NULL, 1},
        {"no-manifest", no_argument, NULL, 2},
        {"sync-method", required_argument, NULL, 3},
        {"clone", no_argument, NULL, 4},
        {"copy", no_argument, NULL, 5},
        {"copy-file-range", no_argument, NULL, 6},
        {NULL, 0, NULL, 0}
    };
 
    const char *progname;
    char       *last_input_dir;
    int         i;
    int         optindex;
    int         c;
    int         n_backups;
    int         n_prior_backups;
    uint32      version;
    uint64      system_identifier;
    char      **prior_backup_dirs;
    cb_options  opt;
    cb_tablespace *tablespaces;
    cb_tablespace *ts;
    StringInfo  last_backup_label;
    manifest_data **manifests;
    manifest_writer *mwriter;
    char       *pgdata;
 
    pg_logging_init(argv[0]);
    progname = get_progname(argv[0]);
    set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_combinebackup"));
    handle_help_version_opts(argc, argv, progname, help);
 
    memset(&opt, 0, sizeof(opt));
    opt.manifest_checksums = CHECKSUM_TYPE_CRC32C;
    opt.sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
    opt.copy_method = COPY_METHOD_COPY;
 
    /* process command-line options */
    while ((c = getopt_long(argc, argv, "dknNo:T:",
                            long_options, &optindex)) != -1)
    {
        switch (c)
        {
            case 'd':
                opt.debug = true;
                pg_logging_increase_verbosity();
                break;
            case 'k':
                opt.copy_method = COPY_METHOD_LINK;
                break;
            case 'n':
                opt.dry_run = true;
                break;
            case 'N':
                opt.no_sync = true;
                break;
            case 'o':
                opt.output = optarg;
                break;
            case 'T':
                add_tablespace_mapping(&opt, optarg);
                break;
            case 1:
                if (!pg_checksum_parse_type(optarg,
                                            &opt.manifest_checksums))
                    pg_fatal("unrecognized checksum algorithm: \"%s\"",
                             optarg);
                break;
            case 2:
                opt.no_manifest = true;
                break;
            case 3:
                if (!parse_sync_method(optarg, &opt.sync_method))
                    exit(1);
                break;
            case 4:
                opt.copy_method = COPY_METHOD_CLONE;
                break;
            case 5:
                opt.copy_method = COPY_METHOD_COPY;
                break;
            case 6:
                opt.copy_method = COPY_METHOD_COPY_FILE_RANGE;
                break;
            default:
                /* getopt_long already emitted a complaint */
                pg_log_error_hint("Try \"%s --help\" for more information.", progname);
                exit(1);
        }
    }
 
    if (optind >= argc)
    {
        pg_log_error("no input directories specified");
        pg_log_error_hint("Try \"%s --help\" for more information.", progname);
        exit(1);
    }
 
    if (opt.output == NULL)
        pg_fatal("no output directory specified");
 
    /* If no manifest is needed, no checksums are needed, either. */
    if (opt.no_manifest)
        opt.manifest_checksums = CHECKSUM_TYPE_NONE;
 
    if (opt.dry_run)
        pg_log_info("Executing in dry-run mode.\n"
                    "The target directory will not be modified.");
 
    /* Check that the platform supports the requested copy method. */
    if (opt.copy_method == COPY_METHOD_CLONE)
    {
#if (defined(HAVE_COPYFILE) && defined(COPYFILE_CLONE_FORCE)) || \
    (defined(__linux__) && defined(FICLONE))
 
        if (opt.dry_run)
            pg_log_debug("would use cloning to copy files");
        else
            pg_log_debug("will use cloning to copy files");
 
#else
        pg_fatal("file cloning not supported on this platform");
#endif
    }
    else if (opt.copy_method == COPY_METHOD_COPY_FILE_RANGE)
    {
#if defined(HAVE_COPY_FILE_RANGE)
 
        if (opt.dry_run)
            pg_log_debug("would use copy_file_range to copy blocks");
        else
            pg_log_debug("will use copy_file_range to copy blocks");
 
#else
        pg_fatal("copy_file_range not supported on this platform");
#endif
    }
 
    /* Read the server version from the final backup. */
    pgdata = argv[argc - 1];
    version = get_pg_version(pgdata, NULL);
    if (GET_PG_MAJORVERSION_NUM(version) < 10)
        pg_fatal("server version too old");
    pg_log_debug("read server version %u from file \"%s/%s\"",
                 GET_PG_MAJORVERSION_NUM(version), pgdata, "PG_VERSION");
 
    /* Sanity-check control files. */
    n_backups = argc - optind;
    system_identifier = check_control_files(n_backups, argv + optind);
 
    /* Sanity-check backup_label files, and get the contents of the last one. */
    last_backup_label = check_backup_label_files(n_backups, argv + optind);
 
    /*
     * We'll need the pathnames to the prior backups. By "prior" we mean all
     * but the last one listed on the command line.
     */
    n_prior_backups = argc - optind - 1;
    prior_backup_dirs = argv + optind;
 
    /* Load backup manifests. */
    manifests = load_backup_manifests(n_backups, prior_backup_dirs);
 
    /*
     * Validate the manifest system identifier against the backup system
     * identifier.
     */
    for (i = 0; i < n_backups; i++)
    {
        if (manifests[i] &&
            manifests[i]->system_identifier != system_identifier)
        {
            char       *controlpath;
 
            controlpath = psprintf("%s/%s", prior_backup_dirs[i], XLOG_CONTROL_FILE);
 
            pg_fatal("%s: manifest system identifier is %" PRIu64 ", but control file has %" PRIu64,
                     controlpath,
                     manifests[i]->system_identifier,
                     system_identifier);
        }
    }
 
    /* Figure out which tablespaces are going to be included in the output. */
    last_input_dir = argv[argc - 1];
    check_input_dir_permissions(last_input_dir);
    tablespaces = scan_for_existing_tablespaces(last_input_dir, &opt);
 
    /*
     * Create output directories.
     *
     * We create one output directory for the main data directory plus one for
     * each non-in-place tablespace. create_output_directory() will arrange
     * for those directories to be cleaned up on failure. In-place tablespaces
     * aren't handled at this stage because they're located beneath the main
     * output directory, and thus the cleanup of that directory will get rid
     * of them. Plus, the pg_tblspc directory that needs to contain them
     * doesn't exist yet.
     */
    atexit(cleanup_directories_atexit);
    create_output_directory(opt.output, &opt);
    for (ts = tablespaces; ts != NULL; ts = ts->next)
        if (!ts->in_place)
            create_output_directory(ts->new_dir, &opt);
 
    /* If we need to write a backup_manifest, prepare to do so. */
    if (!opt.dry_run && !opt.no_manifest)
    {
        mwriter = create_manifest_writer(opt.output, system_identifier);
 
        /*
         * Verify that we have a backup manifest for the final backup; else we
         * won't have the WAL ranges for the resulting manifest.
         */
        if (manifests[n_prior_backups] == NULL)
            pg_fatal("cannot generate a manifest because no manifest is available for the final input backup");
    }
    else
        mwriter = NULL;
 
    /* Write backup label into output directory. */
    if (opt.dry_run)
        pg_log_debug("would generate \"%s/backup_label\"", opt.output);
    else
    {
        pg_log_debug("generating \"%s/backup_label\"", opt.output);
        last_backup_label->cursor = 0;
        write_backup_label(opt.output, last_backup_label,
                           opt.manifest_checksums, mwriter);
    }
 
    /* Process everything that's not part of a user-defined tablespace. */
    pg_log_debug("processing backup directory \"%s\"", last_input_dir);
    process_directory_recursively(InvalidOid, last_input_dir, opt.output,
                                  NULL, n_prior_backups, prior_backup_dirs,
                                  manifests, mwriter, &opt);
 
    /* Process user-defined tablespaces. */
    for (ts = tablespaces; ts != NULL; ts = ts->next)
    {
        pg_log_debug("processing tablespace directory \"%s\"", ts->old_dir);
 
        /*
         * If it's a normal tablespace, we need to set up a symbolic link from
         * pg_tblspc/${OID} to the target directory; if it's an in-place
         * tablespace, we need to create a directory at pg_tblspc/${OID}.
         */
        if (!ts->in_place)
        {
            char        linkpath[MAXPGPATH];
 
            snprintf(linkpath, MAXPGPATH, "%s/%s/%u", opt.output, PG_TBLSPC_DIR,
                     ts->oid);
 
            if (opt.dry_run)
                pg_log_debug("would create symbolic link from \"%s\" to \"%s\"",
                             linkpath, ts->new_dir);
            else
            {
                pg_log_debug("creating symbolic link from \"%s\" to \"%s\"",
                             linkpath, ts->new_dir);
                if (symlink(ts->new_dir, linkpath) != 0)
                    pg_fatal("could not create symbolic link from \"%s\" to \"%s\": %m",
                             linkpath, ts->new_dir);
            }
        }
        else
        {
            if (opt.dry_run)
                pg_log_debug("would create directory \"%s\"", ts->new_dir);
            else
            {
                pg_log_debug("creating directory \"%s\"", ts->new_dir);
                if (pg_mkdir_p(ts->new_dir, pg_dir_create_mode) == -1)
                    pg_fatal("could not create directory \"%s\": %m",
                             ts->new_dir);
            }
        }
 
        /* OK, now handle the directory contents. */
        process_directory_recursively(ts->oid, ts->old_dir, ts->new_dir,
                                      NULL, n_prior_backups, prior_backup_dirs,
                                      manifests, mwriter, &opt);
    }
 
    /* Finalize the backup_manifest, if we're generating one. */
    if (mwriter != NULL)
        finalize_manifest(mwriter,
                          manifests[n_prior_backups]->first_wal_range);
 
    /* fsync that output directory unless we've been told not to do so */
    if (!opt.no_sync)
    {
        if (opt.dry_run)
            pg_log_debug("would recursively fsync \"%s\"", opt.output);
        else
        {
            pg_log_debug("recursively fsyncing \"%s\"", opt.output);
            sync_pgdata(opt.output, version, opt.sync_method, true);
        }
    }
 
    /* Warn about the possibility of compromising the backups, when link mode */
    if (opt.copy_method == COPY_METHOD_LINK)
        pg_log_warning("--link mode was used; any modifications to the output "
                       "directory might destructively modify input directories");
 
    /* It's a success, so don't remove the output directories. */
    reset_directory_cleanup_list();
    exit(0);
}
 
/*
 * Process the option argument for the -T, --tablespace-mapping switch.
 */
static void
add_tablespace_mapping(cb_options *opt, char *arg)
{
    cb_tablespace_mapping *tsmap = pg_malloc0(sizeof(cb_tablespace_mapping));
    char       *dst;
    char       *dst_ptr;
    char       *arg_ptr;
 
    /*
     * Basically, we just want to copy everything before the equals sign to
     * tsmap->old_dir and everything afterwards to tsmap->new_dir, but if
     * there's more or less than one equals sign, that's an error, and if
     * there's an equals sign preceded by a backslash, don't treat it as a
     * field separator but instead copy a literal equals sign.
     */
    dst_ptr = dst = tsmap->old_dir;
    for (arg_ptr = arg; *arg_ptr != '\0'; arg_ptr++)
    {
        if (dst_ptr - dst >= MAXPGPATH)
            pg_fatal("directory name too long");
 
        if (*arg_ptr == '\\' && *(arg_ptr + 1) == '=')
            ;                   /* skip backslash escaping = */
        else if (*arg_ptr == '=' && (arg_ptr == arg || *(arg_ptr - 1) != '\\'))
        {
            if (tsmap->new_dir[0] != '\0')
                pg_fatal("multiple \"=\" signs in tablespace mapping");
            else
                dst = dst_ptr = tsmap->new_dir;
        }
        else
            *dst_ptr++ = *arg_ptr;
    }
    if (!tsmap->old_dir[0] || !tsmap->new_dir[0])
        pg_fatal("invalid tablespace mapping format \"%s\", must be \"OLDDIR=NEWDIR\"", arg);
 
    /*
     * All tablespaces are created with absolute directories, so specifying a
     * non-absolute path here would never match, possibly confusing users.
     *
     * In contrast to pg_basebackup, both the old and new directories are on
     * the local machine, so the local machine's definition of an absolute
     * path is the only relevant one.
     */
    if (!is_absolute_path(tsmap->old_dir))
        pg_fatal("old directory is not an absolute path in tablespace mapping: %s",
                 tsmap->old_dir);
 
    if (!is_absolute_path(tsmap->new_dir))
        pg_fatal("old directory is not an absolute path in tablespace mapping: %s",
                 tsmap->new_dir);
 
    /* Canonicalize paths to avoid spurious failures when comparing. */
    canonicalize_path(tsmap->old_dir);
    canonicalize_path(tsmap->new_dir);
 
    /* Add it to the list. */
    tsmap->next = opt->tsmappings;
    opt->tsmappings = tsmap;
}
 
/*
 * Check that the backup_label files form a coherent backup chain, and return
 * the contents of the backup_label file from the latest backup.
 */
static StringInfo
check_backup_label_files(int n_backups, char **backup_dirs)
{
    StringInfo  buf = makeStringInfo();
    StringInfo  lastbuf = buf;
    int         i;
    TimeLineID  check_tli = 0;
    XLogRecPtr  check_lsn = InvalidXLogRecPtr;
 
    /* Try to read each backup_label file in turn, last to first. */
    for (i = n_backups - 1; i >= 0; --i)
    {
        char        pathbuf[MAXPGPATH];
        int         fd;
        TimeLineID  start_tli;
        TimeLineID  previous_tli;
        XLogRecPtr  start_lsn;
        XLogRecPtr  previous_lsn;
 
        /* Open the backup_label file. */
        snprintf(pathbuf, MAXPGPATH, "%s/backup_label", backup_dirs[i]);
        pg_log_debug("reading \"%s\"", pathbuf);
        if ((fd = open(pathbuf, O_RDONLY, 0)) < 0)
            pg_fatal("could not open file \"%s\": %m", pathbuf);
 
        /*
         * Slurp the whole file into memory.
         *
         * The exact size limit that we impose here doesn't really matter --
         * most of what's supposed to be in the file is fixed size and quite
         * short. However, the length of the backup_label is limited (at least
         * by some parts of the code) to MAXPGPATH, so include that value in
         * the maximum length that we tolerate.
         */
        slurp_file(fd, pathbuf, buf, 10000 + MAXPGPATH);
 
        /* Close the file. */
        if (close(fd) != 0)
            pg_fatal("could not close file \"%s\": %m", pathbuf);
 
        /* Parse the file contents. */
        parse_backup_label(pathbuf, buf, &start_tli, &start_lsn,
                           &previous_tli, &previous_lsn);
 
        /*
         * Sanity checks.
         *
         * XXX. It's actually not required that start_lsn == check_lsn. It
         * would be OK if start_lsn > check_lsn provided that start_lsn is
         * less than or equal to the relevant switchpoint. But at the moment
         * we don't have that information.
         */
        if (i > 0 && previous_tli == 0)
            pg_fatal("backup at \"%s\" is a full backup, but only the first backup should be a full backup",
                     backup_dirs[i]);
        if (i == 0 && previous_tli != 0)
            pg_fatal("backup at \"%s\" is an incremental backup, but the first backup should be a full backup",
                     backup_dirs[i]);
        if (i < n_backups - 1 && start_tli != check_tli)
            pg_fatal("backup at \"%s\" starts on timeline %u, but expected %u",
                     backup_dirs[i], start_tli, check_tli);
        if (i < n_backups - 1 && start_lsn != check_lsn)
            pg_fatal("backup at \"%s\" starts at LSN %X/%08X, but expected %X/%08X",
                     backup_dirs[i],
                     LSN_FORMAT_ARGS(start_lsn),
                     LSN_FORMAT_ARGS(check_lsn));
        check_tli = previous_tli;
        check_lsn = previous_lsn;
 
        /*
         * The last backup label in the chain needs to be saved for later use,
         * while the others are only needed within this loop.
         */
        if (lastbuf == buf)
            buf = makeStringInfo();
        else
            resetStringInfo(buf);
    }
 
    /* Free memory that we don't need any more. */
    if (lastbuf != buf)
        destroyStringInfo(buf);
 
    /*
     * Return the data from the first backup_info that we read (which is the
     * backup_label from the last directory specified on the command line).
     */
    return lastbuf;
}
 
/*
 * Sanity check control files and return system_identifier.
 */
static uint64
check_control_files(int n_backups, char **backup_dirs)
{
    int         i;
    uint64      system_identifier = 0;  /* placate compiler */
    uint32      data_checksum_version = 0;  /* placate compiler */
    bool        data_checksum_mismatch = false;
 
    /* Try to read each control file in turn, last to first. */
    for (i = n_backups - 1; i >= 0; --i)
    {
        ControlFileData *control_file;
        bool        crc_ok;
        char       *controlpath;
 
        controlpath = psprintf("%s/%s", backup_dirs[i], XLOG_CONTROL_FILE);
        pg_log_debug("reading \"%s\"", controlpath);
        control_file = get_controlfile_by_exact_path(controlpath, &crc_ok);
 
        /* Control file contents not meaningful if CRC is bad. */
        if (!crc_ok)
            pg_fatal("%s: CRC is incorrect", controlpath);
 
        /* Can't interpret control file if not current version. */
        if (control_file->pg_control_version != PG_CONTROL_VERSION)
            pg_fatal("%s: unexpected control file version",
                     controlpath);
 
        /* System identifiers should all match. */
        if (i == n_backups - 1)
            system_identifier = control_file->system_identifier;
        else if (system_identifier != control_file->system_identifier)
            pg_fatal("%s: expected system identifier %" PRIu64 ", but found %" PRIu64,
                     controlpath, system_identifier,
                     control_file->system_identifier);
 
        /*
         * Detect checksum mismatches, but only if the last backup in the
         * chain has checksums enabled.
         */
        if (i == n_backups - 1)
            data_checksum_version = control_file->data_checksum_version;
        else if (data_checksum_version != 0 &&
                 data_checksum_version != control_file->data_checksum_version)
            data_checksum_mismatch = true;
 
        /* Release memory. */
        pfree(control_file);
        pfree(controlpath);
    }
 
    /*
     * If debug output is enabled, make a note of the system identifier that
     * we found in all of the relevant control files.
     */
    pg_log_debug("system identifier is %" PRIu64, system_identifier);
 
    /*
     * Warn the user if not all backups are in the same state with regards to
     * checksums.
     */
    if (data_checksum_mismatch)
    {
        pg_log_warning("only some backups have checksums enabled");
        pg_log_warning_hint("Disable, and optionally reenable, checksums on the output directory to avoid failures.");
    }
 
    return system_identifier;
}
 
/*
 * Set default permissions for new files and directories based on the
 * permissions of the given directory. The intent here is that the output
 * directory should use the same permissions scheme as the final input
 * directory.
 */
static void
check_input_dir_permissions(char *dir)
{
    struct stat st;
 
    if (stat(dir, &st) != 0)
        pg_fatal("could not stat file \"%s\": %m", dir);
 
    SetDataDirectoryCreatePerm(st.st_mode);
}
 
/*
 * Clean up output directories before exiting.
 */
static void
cleanup_directories_atexit(void)
{
    while (cleanup_dir_list != NULL)
    {
        cb_cleanup_dir *dir = cleanup_dir_list;
 
        if (dir->rmtopdir)
        {
            pg_log_info("removing output directory \"%s\"", dir->target_path);
            if (!rmtree(dir->target_path, dir->rmtopdir))
                pg_log_error("failed to remove output directory");
        }
        else
        {
            pg_log_info("removing contents of output directory \"%s\"",
                        dir->target_path);
            if (!rmtree(dir->target_path, dir->rmtopdir))
                pg_log_error("failed to remove contents of output directory");
        }
 
        cleanup_dir_list = cleanup_dir_list->next;
        pfree(dir);
    }
}
 
/*
 * Create the named output directory, unless it already exists or we're in
 * dry-run mode. If it already exists but is not empty, that's a fatal error.
 *
 * Adds the created directory to the list of directories to be cleaned up
 * at process exit.
 */
static void
create_output_directory(char *dirname, cb_options *opt)
{
    switch (pg_check_dir(dirname))
    {
        case 0:
            if (opt->dry_run)
            {
                pg_log_debug("would create directory \"%s\"", dirname);
                return;
            }
            pg_log_debug("creating directory \"%s\"", dirname);
            if (pg_mkdir_p(dirname, pg_dir_create_mode) == -1)
                pg_fatal("could not create directory \"%s\": %m", dirname);
            remember_to_cleanup_directory(dirname, true);
            break;
 
        case 1:
            pg_log_debug("using existing directory \"%s\"", dirname);
            remember_to_cleanup_directory(dirname, false);
            break;
 
        case 2:
        case 3:
        case 4:
            pg_fatal("directory \"%s\" exists but is not empty", dirname);
 
        case -1:
            pg_fatal("could not access directory \"%s\": %m", dirname);
    }
}
 
/*
 * help
 *
 * Prints help page for the program
 *
 * progname: the name of the executed program, such as "pg_combinebackup"
 */
static void
help(const char *progname)
{
    printf(_("%s reconstructs full backups from incrementals.\n\n"), progname);
    printf(_("Usage:\n"));
    printf(_("  %s [OPTION]... DIRECTORY...\n"), progname);
    printf(_("\nOptions:\n"));
    printf(_("  -d, --debug               generate lots of debugging output\n"));
    printf(_("  -k, --link                link files instead of copying\n"));
    printf(_("  -n, --dry-run             do not actually do anything\n"));
    printf(_("  -N, --no-sync             do not wait for changes to be written safely to disk\n"));
    printf(_("  -o, --output=DIRECTORY    output directory\n"));
    printf(_("  -T, --tablespace-mapping=OLDDIR=NEWDIR\n"
             "                            relocate tablespace in OLDDIR to NEWDIR\n"));
    printf(_("      --clone               clone (reflink) files instead of copying\n"));
    printf(_("      --copy                copy files (default)\n"));
    printf(_("      --copy-file-range     copy using copy_file_range() system call\n"));
    printf(_("      --manifest-checksums=SHA{224,256,384,512}|CRC32C|NONE\n"
             "                            use algorithm for manifest checksums\n"));
    printf(_("      --no-manifest         suppress generation of backup manifest\n"));
    printf(_("      --sync-method=METHOD  set method for syncing files to disk\n"));
    printf(_("  -V, --version             output version information, then exit\n"));
    printf(_("  -?, --help                show this help, then exit\n"));
 
    printf(_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
    printf(_("%s home page: <%s>\n"), PACKAGE_NAME, PACKAGE_URL);
}
 
/*
 * Try to parse a string as a non-zero OID without leading zeroes.
 *
 * If it works, return true and set *result to the answer, else return false.
 */
static bool
parse_oid(char *s, Oid *result)
{
    Oid         oid;
    char       *ep;
 
    errno = 0;
    oid = strtoul(s, &ep, 10);
    if (errno != 0 || *ep != '\0' || oid < 1 || oid > PG_UINT32_MAX)
        return false;
 
    *result = oid;
    return true;
}
 
/*
 * Copy files from the input directory to the output directory, reconstructing
 * full files from incremental files as required.
 *
 * If processing a user-defined tablespace, the tsoid should be the OID
 * of that tablespace and input_directory and output_directory should be the
 * toplevel input and output directories for that tablespace. Otherwise,
 * tsoid should be InvalidOid and input_directory and output_directory should
 * be the main input and output directories.
 *
 * relative_path is the path beneath the given input and output directories
 * that we are currently processing. If NULL, it indicates that we're
 * processing the input and output directories themselves.
 *
 * n_prior_backups is the number of prior backups that we have available.
 * This doesn't count the very last backup, which is referenced by
 * input_directory, just the older ones. prior_backup_dirs is an array of
 * the locations of those previous backups.
 */
static void
process_directory_recursively(Oid tsoid,
                              char *input_directory,
                              char *output_directory,
                              char *relative_path,
                              int n_prior_backups,
                              char **prior_backup_dirs,
                              manifest_data **manifests,
                              manifest_writer *mwriter,
                              cb_options *opt)
{
    char        ifulldir[MAXPGPATH];
    char        ofulldir[MAXPGPATH];
    char        manifest_prefix[MAXPGPATH];
    DIR        *dir;
    struct dirent *de;
    bool        is_pg_tblspc = false;
    bool        is_pg_wal = false;
    bool        is_incremental_dir = false;
    manifest_data *latest_manifest = manifests[n_prior_backups];
    pg_checksum_type checksum_type;
 
    /*
     * Classify this directory.
     *
     * We set is_pg_tblspc only for the toplevel pg_tblspc directory, because
     * the symlinks in that specific directory require special handling.
     *
     * We set is_pg_wal for the toplevel WAL directory and all of its
     * subdirectories, because those files are not included in the backup
     * manifest and hence need special treatment. (Since incremental backup
     * does not exist in pre-v10 versions, we don't have to worry about the
     * old pg_xlog naming.)
     *
     * We set is_incremental_dir for directories that can contain incremental
     * files requiring reconstruction. If such files occur outside these
     * directories, we want to just copy them straight to the output
     * directory. This is to protect against a user creating a file with a
     * strange name like INCREMENTAL.config and then complaining that
     * incremental backups don't work properly. The test here is a bit tricky:
     * incremental files occur in subdirectories of base, in pg_global itself,
     * and in subdirectories of pg_tblspc only if in-place tablespaces are
     * used.
     */
    if (OidIsValid(tsoid))
        is_incremental_dir = true;
    else if (relative_path != NULL)
    {
        is_pg_tblspc = strcmp(relative_path, PG_TBLSPC_DIR) == 0;
        is_pg_wal = (strcmp(relative_path, "pg_wal") == 0 ||
                     strncmp(relative_path, "pg_wal/", 7) == 0);
        is_incremental_dir = strncmp(relative_path, "base/", 5) == 0 ||
            strcmp(relative_path, "global") == 0 ||
            strncmp(relative_path, PG_TBLSPC_DIR_SLASH, 10) == 0;
    }
 
    /*
     * If we're under pg_wal, then we don't need checksums, because these
     * files aren't included in the backup manifest. Otherwise use whatever
     * type of checksum is configured.
     */
    if (!is_pg_wal)
        checksum_type = opt->manifest_checksums;
    else
        checksum_type = CHECKSUM_TYPE_NONE;
 
    /*
     * Append the relative path to the input and output directories, and
     * figure out the appropriate prefix to add to files in this directory
     * when looking them up in a backup manifest.
     */
    if (relative_path == NULL)
    {
        strlcpy(ifulldir, input_directory, MAXPGPATH);
        strlcpy(ofulldir, output_directory, MAXPGPATH);
        if (OidIsValid(tsoid))
            snprintf(manifest_prefix, MAXPGPATH, "%s/%u/", PG_TBLSPC_DIR, tsoid);
        else
            manifest_prefix[0] = '\0';
    }
    else
    {
        snprintf(ifulldir, MAXPGPATH, "%s/%s", input_directory,
                 relative_path);
        snprintf(ofulldir, MAXPGPATH, "%s/%s", output_directory,
                 relative_path);
        if (OidIsValid(tsoid))
            snprintf(manifest_prefix, MAXPGPATH, "%s/%u/%s/",
                     PG_TBLSPC_DIR, tsoid, relative_path);
        else
            snprintf(manifest_prefix, MAXPGPATH, "%s/", relative_path);
    }
 
    /*
     * Toplevel output directories have already been created by the time this
     * function is called, but any subdirectories are our responsibility.
     */
    if (relative_path != NULL)
    {
        if (opt->dry_run)
            pg_log_debug("would create directory \"%s\"", ofulldir);
        else
        {
            pg_log_debug("creating directory \"%s\"", ofulldir);
            if (mkdir(ofulldir, pg_dir_create_mode) == -1)
                pg_fatal("could not create directory \"%s\": %m", ofulldir);
        }
    }
 
    /* It's time to scan the directory. */
    if ((dir = opendir(ifulldir)) == NULL)
        pg_fatal("could not open directory \"%s\": %m", ifulldir);
    while (errno = 0, (de = readdir(dir)) != NULL)
    {
        PGFileType  type;
        char        ifullpath[MAXPGPATH];
        char        ofullpath[MAXPGPATH];
        char        manifest_path[MAXPGPATH];
        Oid         oid = InvalidOid;
        int         checksum_length = 0;
        uint8      *checksum_payload = NULL;
        pg_checksum_context checksum_ctx;
 
        /* Ignore "." and ".." entries. */
        if (strcmp(de->d_name, ".") == 0 ||
            strcmp(de->d_name, "..") == 0)
            continue;
 
        /* Construct input path. */
        snprintf(ifullpath, MAXPGPATH, "%s/%s", ifulldir, de->d_name);
 
        /* Figure out what kind of directory entry this is. */
        type = get_dirent_type(ifullpath, de, false, PG_LOG_ERROR);
        if (type == PGFILETYPE_ERROR)
            exit(1);
 
        /*
         * If we're processing pg_tblspc, then check whether the filename
         * looks like it could be a tablespace OID. If so, and if the
         * directory entry is a symbolic link or a directory, skip it.
         *
         * Our goal here is to ignore anything that would have been considered
         * by scan_for_existing_tablespaces to be a tablespace.
         */
        if (is_pg_tblspc && parse_oid(de->d_name, &oid) &&
            (type == PGFILETYPE_LNK || type == PGFILETYPE_DIR))
            continue;
 
        /* If it's a directory, recurse. */
        if (type == PGFILETYPE_DIR)
        {
            char        new_relative_path[MAXPGPATH];
 
            /* Append new pathname component to relative path. */
            if (relative_path == NULL)
                strlcpy(new_relative_path, de->d_name, MAXPGPATH);
            else
                snprintf(new_relative_path, MAXPGPATH, "%s/%s", relative_path,
                         de->d_name);
 
            /* And recurse. */
            process_directory_recursively(tsoid,
                                          input_directory, output_directory,
                                          new_relative_path,
                                          n_prior_backups, prior_backup_dirs,
                                          manifests, mwriter, opt);
            continue;
        }
 
        /* Skip anything that's not a regular file. */
        if (type != PGFILETYPE_REG)
        {
            if (type == PGFILETYPE_LNK)
                pg_log_warning("skipping symbolic link \"%s\"", ifullpath);
            else
                pg_log_warning("skipping special file \"%s\"", ifullpath);
            continue;
        }
 
        /*
         * Skip the backup_label and backup_manifest files; they require
         * special handling and are handled elsewhere.
         */
        if (relative_path == NULL &&
            (strcmp(de->d_name, "backup_label") == 0 ||
             strcmp(de->d_name, "backup_manifest") == 0))
            continue;
 
        /*
         * If it's an incremental file, hand it off to the reconstruction
         * code, which will figure out what to do.
         */
        if (is_incremental_dir &&
            strncmp(de->d_name, INCREMENTAL_PREFIX,
                    INCREMENTAL_PREFIX_LENGTH) == 0)
        {
            /* Output path should not include "INCREMENTAL." prefix. */
            snprintf(ofullpath, MAXPGPATH, "%s/%s", ofulldir,
                     de->d_name + INCREMENTAL_PREFIX_LENGTH);
 
 
            /* Manifest path likewise omits incremental prefix. */
            snprintf(manifest_path, MAXPGPATH, "%s%s", manifest_prefix,
                     de->d_name + INCREMENTAL_PREFIX_LENGTH);
 
            /* Reconstruction logic will do the rest. */
            reconstruct_from_incremental_file(ifullpath, ofullpath,
                                              manifest_prefix,
                                              de->d_name + INCREMENTAL_PREFIX_LENGTH,
                                              n_prior_backups,
                                              prior_backup_dirs,
                                              manifests,
                                              manifest_path,
                                              checksum_type,
                                              &checksum_length,
                                              &checksum_payload,
                                              opt->copy_method,
                                              opt->debug,
                                              opt->dry_run);
        }
        else
        {
            /* Construct the path that the backup_manifest will use. */
            snprintf(manifest_path, MAXPGPATH, "%s%s", manifest_prefix,
                     de->d_name);
 
            /*
             * It's not an incremental file, so we need to copy the entire
             * file to the output directory.
             *
             * If a checksum of the required type already exists in the
             * backup_manifest for the final input directory, we can save some
             * work by reusing that checksum instead of computing a new one.
             */
            if (checksum_type != CHECKSUM_TYPE_NONE &&
                latest_manifest != NULL)
            {
                manifest_file *mfile;
 
                mfile = manifest_files_lookup(latest_manifest->files,
                                              manifest_path);
                if (mfile == NULL)
                {
                    char       *bmpath;
 
                    /*
                     * The directory is out of sync with the backup_manifest,
                     * so emit a warning.
                     */
                    bmpath = psprintf("%s/%s", input_directory,
                                      "backup_manifest");
                    pg_log_warning("manifest file \"%s\" contains no entry for file \"%s\"",
                                   bmpath, manifest_path);
                    pfree(bmpath);
                }
                else if (mfile->checksum_type == checksum_type)
                {
                    checksum_length = mfile->checksum_length;
                    checksum_payload = mfile->checksum_payload;
                }
            }
 
            /*
             * If we're reusing a checksum, then we don't need copy_file() to
             * compute one for us, but otherwise, it needs to compute whatever
             * type of checksum we need.
             */
            if (checksum_length != 0)
                pg_checksum_init(&checksum_ctx, CHECKSUM_TYPE_NONE);
            else
                pg_checksum_init(&checksum_ctx, checksum_type);
 
            /* Actually copy the file. */
            snprintf(ofullpath, MAXPGPATH, "%s/%s", ofulldir, de->d_name);
            copy_file(ifullpath, ofullpath, &checksum_ctx,
                      opt->copy_method, opt->dry_run);
 
            /*
             * If copy_file() performed a checksum calculation for us, then
             * save the results (except in dry-run mode, when there's no
             * point).
             */
            if (checksum_ctx.type != CHECKSUM_TYPE_NONE && !opt->dry_run)
            {
                checksum_payload = pg_malloc(PG_CHECKSUM_MAX_LENGTH);
                checksum_length = pg_checksum_final(&checksum_ctx,
                                                    checksum_payload);
            }
        }
 
        /* Generate manifest entry, if needed. */
        if (mwriter != NULL)
        {
            struct stat sb;
 
            /*
             * In order to generate a manifest entry, we need the file size
             * and mtime. We have no way to know the correct mtime except to
             * stat() the file, so just do that and get the size as well.
             *
             * If we didn't need the mtime here, we could try to obtain the
             * file size from the reconstruction or file copy process above,
             * although that is actually not convenient in all cases. If we
             * write the file ourselves then clearly we can keep a count of
             * bytes, but if we use something like CopyFile() then it's
             * trickier. Since we have to stat() anyway to get the mtime,
             * there's no point in worrying about it.
             */
            if (stat(ofullpath, &sb) < 0)
                pg_fatal("could not stat file \"%s\": %m", ofullpath);
 
            /* OK, now do the work. */
            add_file_to_manifest(mwriter, manifest_path,
                                 sb.st_size, sb.st_mtime,
                                 checksum_type, checksum_length,
                                 checksum_payload);
        }
 
        /* Avoid leaking memory. */
        if (checksum_payload != NULL)
            pfree(checksum_payload);
    }
 
    closedir(dir);
}
 
/*
 * Add a directory to the list of output directories to clean up.
 */
static void
remember_to_cleanup_directory(char *target_path, bool rmtopdir)
{
    cb_cleanup_dir *dir = pg_malloc(sizeof(cb_cleanup_dir));
 
    dir->target_path = target_path;
    dir->rmtopdir = rmtopdir;
    dir->next = cleanup_dir_list;
    cleanup_dir_list = dir;
}
 
/*
 * Empty out the list of directories scheduled for cleanup at exit.
 *
 * We want to remove the output directories only on a failure, so call this
 * function when we know that the operation has succeeded.
 *
 * Since we only expect this to be called when we're about to exit, we could
 * just set cleanup_dir_list to NULL and be done with it, but we free the
 * memory to be tidy.
 */
static void
reset_directory_cleanup_list(void)
{
    while (cleanup_dir_list != NULL)
    {
        cb_cleanup_dir *dir = cleanup_dir_list;
 
        cleanup_dir_list = cleanup_dir_list->next;
        pfree(dir);
    }
}
 
/*
 * Scan the pg_tblspc directory of the final input backup to get a canonical
 * list of what tablespaces are part of the backup.
 *
 * 'pathname' should be the path to the toplevel backup directory for the
 * final backup in the backup chain.
 */
static cb_tablespace *
scan_for_existing_tablespaces(char *pathname, cb_options *opt)
{
    char        pg_tblspc[MAXPGPATH];
    DIR        *dir;
    struct dirent *de;
    cb_tablespace *tslist = NULL;
 
    snprintf(pg_tblspc, MAXPGPATH, "%s/%s", pathname, PG_TBLSPC_DIR);
    pg_log_debug("scanning \"%s\"", pg_tblspc);
 
    if ((dir = opendir(pg_tblspc)) == NULL)
        pg_fatal("could not open directory \"%s\": %m", pg_tblspc);
 
    while (errno = 0, (de = readdir(dir)) != NULL)
    {
        Oid         oid;
        char        tblspcdir[MAXPGPATH];
        char        link_target[MAXPGPATH];
        int         link_length;
        cb_tablespace *ts;
        cb_tablespace *otherts;
        PGFileType  type;
 
        /* Silently ignore "." and ".." entries. */
        if (strcmp(de->d_name, ".") == 0 || strcmp(de->d_name, "..") == 0)
            continue;
 
        /* Construct full pathname. */
        snprintf(tblspcdir, MAXPGPATH, "%s/%s", pg_tblspc, de->d_name);
 
        /* Ignore any file name that doesn't look like a proper OID. */
        if (!parse_oid(de->d_name, &oid))
        {
            pg_log_debug("skipping \"%s\" because the filename is not a legal tablespace OID",
                         tblspcdir);
            continue;
        }
 
        /* Only symbolic links and directories are tablespaces. */
        type = get_dirent_type(tblspcdir, de, false, PG_LOG_ERROR);
        if (type == PGFILETYPE_ERROR)
            exit(1);
        if (type != PGFILETYPE_LNK && type != PGFILETYPE_DIR)
        {
            pg_log_debug("skipping \"%s\" because it is neither a symbolic link nor a directory",
                         tblspcdir);
            continue;
        }
 
        /* Create a new tablespace object. */
        ts = pg_malloc0(sizeof(cb_tablespace));
        ts->oid = oid;
 
        /*
         * If it's a link, it's not an in-place tablespace. Otherwise, it must
         * be a directory, and thus an in-place tablespace.
         */
        if (type == PGFILETYPE_LNK)
        {
            cb_tablespace_mapping *tsmap;
 
            /* Read the link target. */
            link_length = readlink(tblspcdir, link_target, sizeof(link_target));
            if (link_length < 0)
                pg_fatal("could not read symbolic link \"%s\": %m",
                         tblspcdir);
            if (link_length >= sizeof(link_target))
                pg_fatal("target of symbolic link \"%s\" is too long", tblspcdir);
            link_target[link_length] = '\0';
            if (!is_absolute_path(link_target))
                pg_fatal("target of symbolic link \"%s\" is relative", tblspcdir);
 
            /* Canonicalize the link target. */
            canonicalize_path(link_target);
 
            /*
             * Find the corresponding tablespace mapping and copy the relevant
             * details into the new tablespace entry.
             */
            for (tsmap = opt->tsmappings; tsmap != NULL; tsmap = tsmap->next)
            {
                if (strcmp(tsmap->old_dir, link_target) == 0)
                {
                    strlcpy(ts->old_dir, tsmap->old_dir, MAXPGPATH);
                    strlcpy(ts->new_dir, tsmap->new_dir, MAXPGPATH);
                    ts->in_place = false;
                    break;
                }
            }
 
            /* Every non-in-place tablespace must be mapped. */
            if (tsmap == NULL)
                pg_fatal("tablespace at \"%s\" has no tablespace mapping",
                         link_target);
        }
        else
        {
            /*
             * For an in-place tablespace, there's no separate directory, so
             * we just record the paths within the data directories.
             */
            snprintf(ts->old_dir, MAXPGPATH, "%s/%s", pg_tblspc, de->d_name);
            snprintf(ts->new_dir, MAXPGPATH, "%s/%s/%s", opt->output,
                     PG_TBLSPC_DIR, de->d_name);
            ts->in_place = true;
        }
 
        /* Tablespaces should not share a directory. */
        for (otherts = tslist; otherts != NULL; otherts = otherts->next)
            if (strcmp(ts->new_dir, otherts->new_dir) == 0)
                pg_fatal("tablespaces with OIDs %u and %u both point at directory \"%s\"",
                         otherts->oid, oid, ts->new_dir);
 
        /* Add this tablespace to the list. */
        ts->next = tslist;
        tslist = ts;
    }
 
    if (closedir(dir) != 0)
        pg_fatal("could not close directory \"%s\": %m", pg_tblspc);
 
    return tslist;
}
 
/*
 * Read a file into a StringInfo.
 *
 * fd is used for the actual file I/O, filename for error reporting purposes.
 * A file longer than maxlen is a fatal error.
 */
static void
slurp_file(int fd, char *filename, StringInfo buf, int maxlen)
{
    struct stat st;
    ssize_t     rb;
 
    /* Check file size, and complain if it's too large. */
    if (fstat(fd, &st) != 0)
        pg_fatal("could not stat file \"%s\": %m", filename);
    if (st.st_size > maxlen)
        pg_fatal("file \"%s\" is too large", filename);
 
    /* Make sure we have enough space. */
    enlargeStringInfo(buf, st.st_size);
 
    /* Read the data. */
    rb = read(fd, &buf->data[buf->len], st.st_size);
 
    /*
     * We don't expect any concurrent changes, so we should read exactly the
     * expected number of bytes.
     */
    if (rb != st.st_size)
    {
        if (rb < 0)
            pg_fatal("could not read file \"%s\": %m", filename);
        else
            pg_fatal("could not read file \"%s\": read %zd of %lld",
                     filename, rb, (long long int) st.st_size);
    }
 
    /* Adjust buffer length for new data and restore trailing-\0 invariant */
    buf->len += rb;
    buf->data[buf->len] = '\0';
}