load_manifest.c

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/*-------------------------------------------------------------------------
 *
 * Load data from a backup manifest into memory.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/bin/pg_combinebackup/load_manifest.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <sys/stat.h>
#include <unistd.h>
 
#include "common/hashfn_unstable.h"
#include "common/logging.h"
#include "common/parse_manifest.h"
#include "load_manifest.h"
 
/*
 * For efficiency, we'd like our hash table containing information about the
 * manifest to start out with approximately the correct number of entries.
 * There's no way to know the exact number of entries without reading the whole
 * file, but we can get an estimate by dividing the file size by the estimated
 * number of bytes per line.
 *
 * This could be off by about a factor of two in either direction, because the
 * checksum algorithm has a big impact on the line lengths; e.g. a SHA512
 * checksum is 128 hex bytes, whereas a CRC-32C value is only 8, and there
 * might be no checksum at all.
 */
#define ESTIMATED_BYTES_PER_MANIFEST_LINE   100
 
/*
 * size of json chunk to be read in
 *
 */
#define READ_CHUNK_SIZE (128  * 1024)
 
/*
 * Define a hash table which we can use to store information about the files
 * mentioned in the backup manifest.
 */
#define SH_PREFIX       manifest_files
#define SH_ELEMENT_TYPE manifest_file
#define SH_KEY_TYPE     const char *
#define SH_KEY          pathname
#define SH_HASH_KEY(tb, key)    hash_string(key)
#define SH_EQUAL(tb, a, b)      (strcmp(a, b) == 0)
#define SH_SCOPE        extern
#define SH_RAW_ALLOCATOR    pg_malloc0
#define SH_DEFINE
#include "lib/simplehash.h"
 
static void combinebackup_version_cb(JsonManifestParseContext *context,
                                     int manifest_version);
static void combinebackup_system_identifier_cb(JsonManifestParseContext *context,
                                               uint64 manifest_system_identifier);
static void combinebackup_per_file_cb(JsonManifestParseContext *context,
                                      const char *pathname, uint64 size,
                                      pg_checksum_type checksum_type,
                                      int checksum_length,
                                      uint8 *checksum_payload);
static void combinebackup_per_wal_range_cb(JsonManifestParseContext *context,
                                           TimeLineID tli,
                                           XLogRecPtr start_lsn,
                                           XLogRecPtr end_lsn);
pg_noreturn static void report_manifest_error(JsonManifestParseContext *context,
                                              const char *fmt,...)
            pg_attribute_printf(2, 3);
 
/*
 * Load backup_manifest files from an array of backups and produces an array
 * of manifest_data objects.
 *
 * NB: Since load_backup_manifest() can return NULL, the resulting array could
 * contain NULL entries.
 */
manifest_data **
load_backup_manifests(int n_backups, char **backup_directories)
{
    manifest_data **result;
    int         i;
 
    result = pg_malloc(sizeof(manifest_data *) * n_backups);
    for (i = 0; i < n_backups; ++i)
        result[i] = load_backup_manifest(backup_directories[i]);
 
    return result;
}
 
/*
 * Parse the backup_manifest file in the named backup directory. Construct a
 * hash table with information about all the files it mentions, and a linked
 * list of all the WAL ranges it mentions.
 *
 * If the backup_manifest file simply doesn't exist, logs a warning and returns
 * NULL. Any other error, or any error parsing the contents of the file, is
 * fatal.
 */
manifest_data *
load_backup_manifest(char *backup_directory)
{
    char        pathname[MAXPGPATH];
    int         fd;
    struct stat statbuf;
    off_t       estimate;
    uint32      initial_size;
    manifest_files_hash *ht;
    char       *buffer;
    int         rc;
    JsonManifestParseContext context;
    manifest_data *result;
    int         chunk_size = READ_CHUNK_SIZE;
 
    /* Open the manifest file. */
    snprintf(pathname, MAXPGPATH, "%s/backup_manifest", backup_directory);
    if ((fd = open(pathname, O_RDONLY | PG_BINARY, 0)) < 0)
    {
        if (errno == ENOENT)
        {
            pg_log_warning("file \"%s\" does not exist", pathname);
            return NULL;
        }
        pg_fatal("could not open file \"%s\": %m", pathname);
    }
 
    /* Figure out how big the manifest is. */
    if (fstat(fd, &statbuf) != 0)
        pg_fatal("could not stat file \"%s\": %m", pathname);
 
    /* Guess how large to make the hash table based on the manifest size. */
    estimate = statbuf.st_size / ESTIMATED_BYTES_PER_MANIFEST_LINE;
    initial_size = Min(PG_UINT32_MAX, Max(estimate, 256));
 
    /* Create the hash table. */
    ht = manifest_files_create(initial_size, NULL);
 
    result = pg_malloc0(sizeof(manifest_data));
    result->files = ht;
    context.private_data = result;
    context.version_cb = combinebackup_version_cb;
    context.system_identifier_cb = combinebackup_system_identifier_cb;
    context.per_file_cb = combinebackup_per_file_cb;
    context.per_wal_range_cb = combinebackup_per_wal_range_cb;
    context.error_cb = report_manifest_error;
 
    /*
     * Parse the file, in chunks if necessary.
     */
    if (statbuf.st_size <= chunk_size)
    {
        buffer = pg_malloc(statbuf.st_size);
        rc = read(fd, buffer, statbuf.st_size);
        if (rc != statbuf.st_size)
        {
            if (rc < 0)
                pg_fatal("could not read file \"%s\": %m", pathname);
            else
                pg_fatal("could not read file \"%s\": read %d of %lld",
                         pathname, rc, (long long int) statbuf.st_size);
        }
 
        /* Close the manifest file. */
        close(fd);
 
        /* Parse the manifest. */
        json_parse_manifest(&context, buffer, statbuf.st_size);
    }
    else
    {
        int         bytes_left = statbuf.st_size;
        JsonManifestParseIncrementalState *inc_state;
 
        inc_state = json_parse_manifest_incremental_init(&context);
 
        buffer = pg_malloc(chunk_size + 1);
 
        while (bytes_left > 0)
        {
            int         bytes_to_read = chunk_size;
 
            /*
             * Make sure that the last chunk is sufficiently large. (i.e. at
             * least half the chunk size) so that it will contain fully the
             * piece at the end with the checksum.
             */
            if (bytes_left < chunk_size)
                bytes_to_read = bytes_left;
            else if (bytes_left < 2 * chunk_size)
                bytes_to_read = bytes_left / 2;
            rc = read(fd, buffer, bytes_to_read);
            if (rc != bytes_to_read)
            {
                if (rc < 0)
                    pg_fatal("could not read file \"%s\": %m", pathname);
                else
                    pg_fatal("could not read file \"%s\": read %lld of %lld",
                             pathname,
                             (long long int) (statbuf.st_size + rc - bytes_left),
                             (long long int) statbuf.st_size);
            }
            bytes_left -= rc;
            json_parse_manifest_incremental_chunk(inc_state, buffer, rc, bytes_left == 0);
        }
 
        /* Release the incremental state memory */
        json_parse_manifest_incremental_shutdown(inc_state);
 
        close(fd);
    }
 
    /* All done. */
    pfree(buffer);
    return result;
}
 
/*
 * Report an error while parsing the manifest.
 *
 * We consider all such errors to be fatal errors. The manifest parser
 * expects this function not to return.
 */
static void
report_manifest_error(JsonManifestParseContext *context, const char *fmt,...)
{
    va_list     ap;
 
    va_start(ap, fmt);
    pg_log_generic_v(PG_LOG_ERROR, PG_LOG_PRIMARY, gettext(fmt), ap);
    va_end(ap);
 
    exit(1);
}
 
/*
 * This callback to validate the manifest version number for incremental backup.
 */
static void
combinebackup_version_cb(JsonManifestParseContext *context,
                         int manifest_version)
{
    /* Incremental backups supported on manifest version 2 or later */
    if (manifest_version == 1)
        pg_fatal("backup manifest version 1 does not support incremental backup");
}
 
/*
 * Record system identifier extracted from the backup manifest.
 */
static void
combinebackup_system_identifier_cb(JsonManifestParseContext *context,
                                   uint64 manifest_system_identifier)
{
    manifest_data *manifest = context->private_data;
 
    /* Validation will be at the later stage */
    manifest->system_identifier = manifest_system_identifier;
}
 
/*
 * Record details extracted from the backup manifest for one file.
 */
static void
combinebackup_per_file_cb(JsonManifestParseContext *context,
                          const char *pathname, uint64 size,
                          pg_checksum_type checksum_type,
                          int checksum_length, uint8 *checksum_payload)
{
    manifest_data *manifest = context->private_data;
    manifest_file *m;
    bool        found;
 
    /* Make a new entry in the hash table for this file. */
    m = manifest_files_insert(manifest->files, pathname, &found);
    if (found)
        pg_fatal("duplicate path name in backup manifest: \"%s\"", pathname);
 
    /* Initialize the entry. */
    m->size = size;
    m->checksum_type = checksum_type;
    m->checksum_length = checksum_length;
    m->checksum_payload = checksum_payload;
}
 
/*
 * Record details extracted from the backup manifest for one WAL range.
 */
static void
combinebackup_per_wal_range_cb(JsonManifestParseContext *context,
                               TimeLineID tli,
                               XLogRecPtr start_lsn, XLogRecPtr end_lsn)
{
    manifest_data *manifest = context->private_data;
    manifest_wal_range *range;
 
    /* Allocate and initialize a struct describing this WAL range. */
    range = palloc(sizeof(manifest_wal_range));
    range->tli = tli;
    range->start_lsn = start_lsn;
    range->end_lsn = end_lsn;
    range->prev = manifest->last_wal_range;
    range->next = NULL;
 
    /* Add it to the end of the list. */
    if (manifest->first_wal_range == NULL)
        manifest->first_wal_range = range;
    else
        manifest->last_wal_range->next = range;
    manifest->last_wal_range = range;
}