filemap.c

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/*-------------------------------------------------------------------------
 *
 * filemap.c
 *    A data structure for keeping track of files that have changed.
 *
 * Copyright (c) 2013-2020, PostgreSQL Global Development Group
 *
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include <sys/stat.h>
#include <unistd.h>

#include "catalog/pg_tablespace_d.h"
#include "common/string.h"
#include "datapagemap.h"
#include "filemap.h"
#include "pg_rewind.h"
#include "storage/fd.h"

filemap_t  *filemap = NULL;

static bool isRelDataFile(const char *path);
static char *datasegpath(RelFileNode rnode, ForkNumber forknum,
                         BlockNumber segno);
static int  path_cmp(const void *a, const void *b);
static int  final_filemap_cmp(const void *a, const void *b);
static void filemap_list_to_array(filemap_t *map);
static bool check_file_excluded(const char *path, bool is_source);

/*
 * Definition of one element part of an exclusion list, used to exclude
 * contents when rewinding.  "name" is the name of the file or path to
 * check for exclusion.  If "match_prefix" is true, any items matching
 * the name as prefix are excluded.
 */
struct exclude_list_item
{
    const char *name;
    bool        match_prefix;
};

/*
 * The contents of these directories are removed or recreated during server
 * start so they are not included in data processed by pg_rewind.
 *
 * Note: those lists should be kept in sync with what basebackup.c provides.
 * Some of the values, contrary to what basebackup.c uses, are hardcoded as
 * they are defined in backend-only headers.  So this list is maintained
 * with a best effort in mind.
 */
static const char *excludeDirContents[] =
{
    /*
     * Skip temporary statistics files. PG_STAT_TMP_DIR must be skipped even
     * when stats_temp_directory is set because PGSS_TEXT_FILE is always
     * created there.
     */
    "pg_stat_tmp",              /* defined as PG_STAT_TMP_DIR */

    /*
     * It is generally not useful to backup the contents of this directory
     * even if the intention is to restore to another master. See backup.sgml
     * for a more detailed description.
     */
    "pg_replslot",

    /* Contents removed on startup, see dsm_cleanup_for_mmap(). */
    "pg_dynshmem",              /* defined as PG_DYNSHMEM_DIR */

    /* Contents removed on startup, see AsyncShmemInit(). */
    "pg_notify",

    /*
     * Old contents are loaded for possible debugging but are not required for
     * normal operation, see OldSerXidInit().
     */
    "pg_serial",

    /* Contents removed on startup, see DeleteAllExportedSnapshotFiles(). */
    "pg_snapshots",

    /* Contents zeroed on startup, see StartupSUBTRANS(). */
    "pg_subtrans",

    /* end of list */
    NULL
};

/*
 * List of files excluded from filemap processing.   Files are excluded
 * if their prefix match.
 */
static const struct exclude_list_item excludeFiles[] =
{
    /* Skip auto conf temporary file. */
    {"postgresql.auto.conf.tmp", false},    /* defined as PG_AUTOCONF_FILENAME */

    /* Skip current log file temporary file */
    {"current_logfiles.tmp", false},    /* defined as
                                         * LOG_METAINFO_DATAFILE_TMP */

    /* Skip relation cache because it is rebuilt on startup */
    {"pg_internal.init", true}, /* defined as RELCACHE_INIT_FILENAME */

    /*
     * If there's a backup_label or tablespace_map file, it belongs to a
     * backup started by the user with pg_start_backup().  It is *not* correct
     * for this backup.  Our backup_label is written later on separately.
     */
    {"backup_label", false},    /* defined as BACKUP_LABEL_FILE */
    {"tablespace_map", false},  /* defined as TABLESPACE_MAP */

    {"postmaster.pid", false},
    {"postmaster.opts", false},

    /* end of list */
    {NULL, false}
};

/*
 * Create a new file map (stored in the global pointer "filemap").
 */
void
filemap_create(void)
{
    filemap_t  *map;

    map = pg_malloc(sizeof(filemap_t));
    map->first = map->last = NULL;
    map->nlist = 0;
    map->array = NULL;
    map->narray = 0;

    Assert(filemap == NULL);
    filemap = map;
}

/*
 * Callback for processing source file list.
 *
 * This is called once for every file in the source server. We decide what
 * action needs to be taken for the file, depending on whether the file
 * exists in the target and whether the size matches.
 */
void
process_source_file(const char *path, file_type_t type, size_t newsize,
                    const char *link_target)
{
    bool        exists;
    char        localpath[MAXPGPATH];
    struct stat statbuf;
    filemap_t  *map = filemap;
    file_action_t action = FILE_ACTION_NONE;
    size_t      oldsize = 0;
    file_entry_t *entry;

    Assert(map->array == NULL);

    /*
     * Skip any files matching the exclusion filters. This has the effect to
     * remove all those files on the target.
     */
    if (check_file_excluded(path, true))
        return;

    /*
     * Pretend that pg_wal is a directory, even if it's really a symlink. We
     * don't want to mess with the symlink itself, nor complain if it's a
     * symlink in source but not in target or vice versa.
     */
    if (strcmp(path, "pg_wal") == 0 && type == FILE_TYPE_SYMLINK)
        type = FILE_TYPE_DIRECTORY;

    /*
     * Skip temporary files, .../pgsql_tmp/... and .../pgsql_tmp.* in source.
     * This has the effect that all temporary files in the destination will be
     * removed.
     */
    if (strstr(path, "/" PG_TEMP_FILE_PREFIX) != NULL)
        return;
    if (strstr(path, "/" PG_TEMP_FILES_DIR "/") != NULL)
        return;

    /*
     * sanity check: a filename that looks like a data file better be a
     * regular file
     */
    if (type != FILE_TYPE_REGULAR && isRelDataFile(path))
        pg_fatal("data file \"%s\" in source is not a regular file", path);

    snprintf(localpath, sizeof(localpath), "%s/%s", datadir_target, path);

    /* Does the corresponding file exist in the target data dir? */
    if (lstat(localpath, &statbuf) < 0)
    {
        if (errno != ENOENT)
            pg_fatal("could not stat file \"%s\": %m",
                     localpath);

        exists = false;
    }
    else
        exists = true;

    switch (type)
    {
        case FILE_TYPE_DIRECTORY:
            if (exists && !S_ISDIR(statbuf.st_mode) && strcmp(path, "pg_wal") != 0)
            {
                /* it's a directory in source, but not in target. Strange.. */
                pg_fatal("\"%s\" is not a directory", localpath);
            }

            if (!exists)
                action = FILE_ACTION_CREATE;
            else
                action = FILE_ACTION_NONE;
            oldsize = 0;
            break;

        case FILE_TYPE_SYMLINK:
            if (exists &&
#ifndef WIN32
                !S_ISLNK(statbuf.st_mode)
#else
                !pgwin32_is_junction(localpath)
#endif
                )
            {
                /*
                 * It's a symbolic link in source, but not in target.
                 * Strange..
                 */
                pg_fatal("\"%s\" is not a symbolic link", localpath);
            }

            if (!exists)
                action = FILE_ACTION_CREATE;
            else
                action = FILE_ACTION_NONE;
            oldsize = 0;
            break;

        case FILE_TYPE_REGULAR:
            if (exists && !S_ISREG(statbuf.st_mode))
                pg_fatal("\"%s\" is not a regular file", localpath);

            if (!exists || !isRelDataFile(path))
            {
                /*
                 * File exists in source, but not in target. Or it's a
                 * non-data file that we have no special processing for. Copy
                 * it in toto.
                 *
                 * An exception: PG_VERSIONs should be identical, but avoid
                 * overwriting it for paranoia.
                 */
                if (pg_str_endswith(path, "PG_VERSION"))
                {
                    action = FILE_ACTION_NONE;
                    oldsize = statbuf.st_size;
                }
                else
                {
                    action = FILE_ACTION_COPY;
                    oldsize = 0;
                }
            }
            else
            {
                /*
                 * It's a data file that exists in both.
                 *
                 * If it's larger in target, we can truncate it. There will
                 * also be a WAL record of the truncation in the source
                 * system, so WAL replay would eventually truncate the target
                 * too, but we might as well do it now.
                 *
                 * If it's smaller in the target, it means that it has been
                 * truncated in the target, or enlarged in the source, or
                 * both. If it was truncated in the target, we need to copy
                 * the missing tail from the source system. If it was enlarged
                 * in the source system, there will be WAL records in the
                 * source system for the new blocks, so we wouldn't need to
                 * copy them here. But we don't know which scenario we're
                 * dealing with, and there's no harm in copying the missing
                 * blocks now, so do it now.
                 *
                 * If it's the same size, do nothing here. Any blocks modified
                 * in the target will be copied based on parsing the target
                 * system's WAL, and any blocks modified in the source will be
                 * updated after rewinding, when the source system's WAL is
                 * replayed.
                 */
                oldsize = statbuf.st_size;
                if (oldsize < newsize)
                    action = FILE_ACTION_COPY_TAIL;
                else if (oldsize > newsize)
                    action = FILE_ACTION_TRUNCATE;
                else
                    action = FILE_ACTION_NONE;
            }
            break;
    }

    /* Create a new entry for this file */
    entry = pg_malloc(sizeof(file_entry_t));
    entry->path = pg_strdup(path);
    entry->type = type;
    entry->action = action;
    entry->oldsize = oldsize;
    entry->newsize = newsize;
    entry->link_target = link_target ? pg_strdup(link_target) : NULL;
    entry->next = NULL;
    entry->pagemap.bitmap = NULL;
    entry->pagemap.bitmapsize = 0;
    entry->isrelfile = isRelDataFile(path);

    if (map->last)
    {
        map->last->next = entry;
        map->last = entry;
    }
    else
        map->first = map->last = entry;
    map->nlist++;
}

/*
 * Callback for processing target file list.
 *
 * All source files must be already processed before calling this. This only
 * marks target data directory's files that didn't exist in the source for
 * deletion.
 */
void
process_target_file(const char *path, file_type_t type, size_t oldsize,
                    const char *link_target)
{
    bool        exists;
    char        localpath[MAXPGPATH];
    struct stat statbuf;
    file_entry_t key;
    file_entry_t *key_ptr;
    filemap_t  *map = filemap;
    file_entry_t *entry;

    /*
     * Do not apply any exclusion filters here.  This has advantage to remove
     * from the target data folder all paths which have been filtered out from
     * the source data folder when processing the source files.
     */

    snprintf(localpath, sizeof(localpath), "%s/%s", datadir_target, path);
    if (lstat(localpath, &statbuf) < 0)
    {
        if (errno != ENOENT)
            pg_fatal("could not stat file \"%s\": %m",
                     localpath);

        exists = false;
    }

    if (map->array == NULL)
    {
        /* on first call, initialize lookup array */
        if (map->nlist == 0)
        {
            /* should not happen */
            pg_fatal("source file list is empty");
        }

        filemap_list_to_array(map);

        Assert(map->array != NULL);

        qsort(map->array, map->narray, sizeof(file_entry_t *), path_cmp);
    }

    /*
     * Like in process_source_file, pretend that xlog is always a  directory.
     */
    if (strcmp(path, "pg_wal") == 0 && type == FILE_TYPE_SYMLINK)
        type = FILE_TYPE_DIRECTORY;

    key.path = (char *) path;
    key_ptr = &key;
    exists = (bsearch(&key_ptr, map->array, map->narray, sizeof(file_entry_t *),
                      path_cmp) != NULL);

    /* Remove any file or folder that doesn't exist in the source system. */
    if (!exists)
    {
        entry = pg_malloc(sizeof(file_entry_t));
        entry->path = pg_strdup(path);
        entry->type = type;
        entry->action = FILE_ACTION_REMOVE;
        entry->oldsize = oldsize;
        entry->newsize = 0;
        entry->link_target = link_target ? pg_strdup(link_target) : NULL;
        entry->next = NULL;
        entry->pagemap.bitmap = NULL;
        entry->pagemap.bitmapsize = 0;
        entry->isrelfile = isRelDataFile(path);

        if (map->last == NULL)
            map->first = entry;
        else
            map->last->next = entry;
        map->last = entry;
        map->nlist++;
    }
    else
    {
        /*
         * We already handled all files that exist in the source system in
         * process_source_file().
         */
    }
}

/*
 * This callback gets called while we read the WAL in the target, for every
 * block that have changed in the target system. It makes note of all the
 * changed blocks in the pagemap of the file.
 */
void
process_block_change(ForkNumber forknum, RelFileNode rnode, BlockNumber blkno)
{
    char       *path;
    file_entry_t key;
    file_entry_t *key_ptr;
    file_entry_t *entry;
    BlockNumber blkno_inseg;
    int         segno;
    filemap_t  *map = filemap;
    file_entry_t **e;

    Assert(map->array);

    segno = blkno / RELSEG_SIZE;
    blkno_inseg = blkno % RELSEG_SIZE;

    path = datasegpath(rnode, forknum, segno);

    key.path = (char *) path;
    key_ptr = &key;

    e = bsearch(&key_ptr, map->array, map->narray, sizeof(file_entry_t *),
                path_cmp);
    if (e)
        entry = *e;
    else
        entry = NULL;
    pfree(path);

    if (entry)
    {
        Assert(entry->isrelfile);

        switch (entry->action)
        {
            case FILE_ACTION_NONE:
            case FILE_ACTION_TRUNCATE:
                /* skip if we're truncating away the modified block anyway */
                if ((blkno_inseg + 1) * BLCKSZ <= entry->newsize)
                    datapagemap_add(&entry->pagemap, blkno_inseg);
                break;

            case FILE_ACTION_COPY_TAIL:

                /*
                 * skip the modified block if it is part of the "tail" that
                 * we're copying anyway.
                 */
                if ((blkno_inseg + 1) * BLCKSZ <= entry->oldsize)
                    datapagemap_add(&entry->pagemap, blkno_inseg);
                break;

            case FILE_ACTION_COPY:
            case FILE_ACTION_REMOVE:
                break;

            case FILE_ACTION_CREATE:
                pg_fatal("unexpected page modification for directory or symbolic link \"%s\"", entry->path);
        }
    }
    else
    {
        /*
         * If we don't have any record of this file in the file map, it means
         * that it's a relation that doesn't exist in the source system, and
         * it was subsequently removed in the target system, too. We can
         * safely ignore it.
         */
    }
}

/*
 * Is this the path of file that pg_rewind can skip copying?
 */
static bool
check_file_excluded(const char *path, bool is_source)
{
    char        localpath[MAXPGPATH];
    int         excludeIdx;
    const char *filename;

    /* check individual files... */
    for (excludeIdx = 0; excludeFiles[excludeIdx].name != NULL; excludeIdx++)
    {
        int         cmplen = strlen(excludeFiles[excludeIdx].name);

        filename = last_dir_separator(path);
        if (filename == NULL)
            filename = path;
        else
            filename++;

        if (!excludeFiles[excludeIdx].match_prefix)
            cmplen++;
        if (strncmp(filename, excludeFiles[excludeIdx].name, cmplen) == 0)
        {
            if (is_source)
                pg_log_debug("entry \"%s\" excluded from source file list",
                             path);
            else
                pg_log_debug("entry \"%s\" excluded from target file list",
                             path);
            return true;
        }
    }

    /*
     * ... And check some directories.  Note that this includes any contents
     * within the directories themselves.
     */
    for (excludeIdx = 0; excludeDirContents[excludeIdx] != NULL; excludeIdx++)
    {
        snprintf(localpath, sizeof(localpath), "%s/",
                 excludeDirContents[excludeIdx]);
        if (strstr(path, localpath) == path)
        {
            if (is_source)
                pg_log_debug("entry \"%s\" excluded from source file list",
                             path);
            else
                pg_log_debug("entry \"%s\" excluded from target file list",
                             path);
            return true;
        }
    }

    return false;
}

/*
 * Convert the linked list of entries in map->first/last to the array,
 * map->array.
 */
static void
filemap_list_to_array(filemap_t *map)
{
    int         narray;
    file_entry_t *entry,
               *next;

    map->array = (file_entry_t **)
        pg_realloc(map->array,
                   (map->nlist + map->narray) * sizeof(file_entry_t *));

    narray = map->narray;
    for (entry = map->first; entry != NULL; entry = next)
    {
        map->array[narray++] = entry;
        next = entry->next;
        entry->next = NULL;
    }
    Assert(narray == map->nlist + map->narray);
    map->narray = narray;
    map->nlist = 0;
    map->first = map->last = NULL;
}

void
filemap_finalize(void)
{
    filemap_t  *map = filemap;

    filemap_list_to_array(map);
    qsort(map->array, map->narray, sizeof(file_entry_t *),
          final_filemap_cmp);
}

static const char *
action_to_str(file_action_t action)
{
    switch (action)
    {
        case FILE_ACTION_NONE:
            return "NONE";
        case FILE_ACTION_COPY:
            return "COPY";
        case FILE_ACTION_TRUNCATE:
            return "TRUNCATE";
        case FILE_ACTION_COPY_TAIL:
            return "COPY_TAIL";
        case FILE_ACTION_CREATE:
            return "CREATE";
        case FILE_ACTION_REMOVE:
            return "REMOVE";

        default:
            return "unknown";
    }
}

/*
 * Calculate the totals needed for progress reports.
 */
void
calculate_totals(void)
{
    file_entry_t *entry;
    int         i;
    filemap_t  *map = filemap;

    map->total_size = 0;
    map->fetch_size = 0;

    for (i = 0; i < map->narray; i++)
    {
        entry = map->array[i];

        if (entry->type != FILE_TYPE_REGULAR)
            continue;

        map->total_size += entry->newsize;

        if (entry->action == FILE_ACTION_COPY)
        {
            map->fetch_size += entry->newsize;
            continue;
        }

        if (entry->action == FILE_ACTION_COPY_TAIL)
            map->fetch_size += (entry->newsize - entry->oldsize);

        if (entry->pagemap.bitmapsize > 0)
        {
            datapagemap_iterator_t *iter;
            BlockNumber blk;

            iter = datapagemap_iterate(&entry->pagemap);
            while (datapagemap_next(iter, &blk))
                map->fetch_size += BLCKSZ;

            pg_free(iter);
        }
    }
}

void
print_filemap(void)
{
    filemap_t  *map = filemap;
    file_entry_t *entry;
    int         i;

    for (i = 0; i < map->narray; i++)
    {
        entry = map->array[i];
        if (entry->action != FILE_ACTION_NONE ||
            entry->pagemap.bitmapsize > 0)
        {
            pg_log_debug("%s (%s)", entry->path,
                         action_to_str(entry->action));

            if (entry->pagemap.bitmapsize > 0)
                datapagemap_print(&entry->pagemap);
        }
    }
    fflush(stdout);
}

/*
 * Does it look like a relation data file?
 *
 * For our purposes, only files belonging to the main fork are considered
 * relation files. Other forks are always copied in toto, because we cannot
 * reliably track changes to them, because WAL only contains block references
 * for the main fork.
 */
static bool
isRelDataFile(const char *path)
{
    RelFileNode rnode;
    unsigned int segNo;
    int         nmatch;
    bool        matched;

    /*----
     * Relation data files can be in one of the following directories:
     *
     * global/
     *      shared relations
     *
     * base/<db oid>/
     *      regular relations, default tablespace
     *
     * pg_tblspc/<tblspc oid>/<tblspc version>/
     *      within a non-default tablespace (the name of the directory
     *      depends on version)
     *
     * And the relation data files themselves have a filename like:
     *
     * <oid>.<segment number>
     *
     *----
     */
    rnode.spcNode = InvalidOid;
    rnode.dbNode = InvalidOid;
    rnode.relNode = InvalidOid;
    segNo = 0;
    matched = false;

    nmatch = sscanf(path, "global/%u.%u", &rnode.relNode, &segNo);
    if (nmatch == 1 || nmatch == 2)
    {
        rnode.spcNode = GLOBALTABLESPACE_OID;
        rnode.dbNode = 0;
        matched = true;
    }
    else
    {
        nmatch = sscanf(path, "base/%u/%u.%u",
                        &rnode.dbNode, &rnode.relNode, &segNo);
        if (nmatch == 2 || nmatch == 3)
        {
            rnode.spcNode = DEFAULTTABLESPACE_OID;
            matched = true;
        }
        else
        {
            nmatch = sscanf(path, "pg_tblspc/%u/" TABLESPACE_VERSION_DIRECTORY "/%u/%u.%u",
                            &rnode.spcNode, &rnode.dbNode, &rnode.relNode,
                            &segNo);
            if (nmatch == 3 || nmatch == 4)
                matched = true;
        }
    }

    /*
     * The sscanf tests above can match files that have extra characters at
     * the end. To eliminate such cases, cross-check that GetRelationPath
     * creates the exact same filename, when passed the RelFileNode
     * information we extracted from the filename.
     */
    if (matched)
    {
        char       *check_path = datasegpath(rnode, MAIN_FORKNUM, segNo);

        if (strcmp(check_path, path) != 0)
            matched = false;

        pfree(check_path);
    }

    return matched;
}

/*
 * A helper function to create the path of a relation file and segment.
 *
 * The returned path is palloc'd
 */
static char *
datasegpath(RelFileNode rnode, ForkNumber forknum, BlockNumber segno)
{
    char       *path;
    char       *segpath;

    path = relpathperm(rnode, forknum);
    if (segno > 0)
    {
        segpath = psprintf("%s.%u", path, segno);
        pfree(path);
        return segpath;
    }
    else
        return path;
}

static int
path_cmp(const void *a, const void *b)
{
    file_entry_t *fa = *((file_entry_t **) a);
    file_entry_t *fb = *((file_entry_t **) b);

    return strcmp(fa->path, fb->path);
}

/*
 * In the final stage, the filemap is sorted so that removals come last.
 * From disk space usage point of view, it would be better to do removals
 * first, but for now, safety first. If a whole directory is deleted, all
 * files and subdirectories inside it need to removed first. On creation,
 * parent directory needs to be created before files and directories inside
 * it. To achieve that, the file_action_t enum is ordered so that we can
 * just sort on that first. Furthermore, sort REMOVE entries in reverse
 * path order, so that "foo/bar" subdirectory is removed before "foo".
 */
static int
final_filemap_cmp(const void *a, const void *b)
{
    file_entry_t *fa = *((file_entry_t **) a);
    file_entry_t *fb = *((file_entry_t **) b);

    if (fa->action > fb->action)
        return 1;
    if (fa->action < fb->action)
        return -1;

    if (fa->action == FILE_ACTION_REMOVE)
        return strcmp(fb->path, fa->path);
    else
        return strcmp(fa->path, fb->path);
}