controldata_utils.c

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/*-------------------------------------------------------------------------
 *
 * controldata_utils.c
 *      Common code for control data file output.
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/common/controldata_utils.c
 *
 *-------------------------------------------------------------------------
 */
 
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <time.h>
 
#include "access/xlog_internal.h"
#include "catalog/pg_control.h"
#include "common/controldata_utils.h"
#ifdef FRONTEND
#include "common/file_perm.h"
#include "common/logging.h"
#endif
#include "port/pg_crc32c.h"
 
#ifndef FRONTEND
#include "pgstat.h"
#include "storage/fd.h"
#endif
 
/*
 * get_controlfile()
 *
 * Get controlfile values.  The result is returned as a palloc'd copy of the
 * control file data.
 *
 * crc_ok_p can be used by the caller to see whether the CRC of the control
 * file data is correct.
 */
ControlFileData *
get_controlfile(const char *DataDir, bool *crc_ok_p)
{
    char        ControlFilePath[MAXPGPATH];
 
    snprintf(ControlFilePath, MAXPGPATH, "%s/%s", DataDir, XLOG_CONTROL_FILE);
 
    return get_controlfile_by_exact_path(ControlFilePath, crc_ok_p);
}
 
/*
 * get_controlfile_by_exact_path()
 *
 * As above, but the caller specifies the path to the control file itself,
 * rather than the path to the data directory.
 */
ControlFileData *
get_controlfile_by_exact_path(const char *ControlFilePath, bool *crc_ok_p)
{
    ControlFileData *ControlFile;
    int         fd;
    pg_crc32c   crc;
    int         r;
#ifdef FRONTEND
    pg_crc32c   last_crc;
    int         retries = 0;
#endif
 
    Assert(crc_ok_p);
 
    ControlFile = palloc_object(ControlFileData);
 
#ifdef FRONTEND
    INIT_CRC32C(last_crc);
 
retry:
#endif
 
#ifndef FRONTEND
    if ((fd = OpenTransientFile(ControlFilePath, O_RDONLY | PG_BINARY)) == -1)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open file \"%s\" for reading: %m",
                        ControlFilePath)));
#else
    if ((fd = open(ControlFilePath, O_RDONLY | PG_BINARY, 0)) == -1)
        pg_fatal("could not open file \"%s\" for reading: %m",
                 ControlFilePath);
#endif
 
    r = read(fd, ControlFile, sizeof(ControlFileData));
    if (r != sizeof(ControlFileData))
    {
        if (r < 0)
#ifndef FRONTEND
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read file \"%s\": %m", ControlFilePath)));
#else
            pg_fatal("could not read file \"%s\": %m", ControlFilePath);
#endif
        else
#ifndef FRONTEND
            ereport(ERROR,
                    (errcode(ERRCODE_DATA_CORRUPTED),
                     errmsg("could not read file \"%s\": read %d of %zu",
                            ControlFilePath, r, sizeof(ControlFileData))));
#else
            pg_fatal("could not read file \"%s\": read %d of %zu",
                     ControlFilePath, r, sizeof(ControlFileData));
#endif
    }
 
#ifndef FRONTEND
    if (CloseTransientFile(fd) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m",
                        ControlFilePath)));
#else
    if (close(fd) != 0)
        pg_fatal("could not close file \"%s\": %m", ControlFilePath);
#endif
 
    /* Check the CRC. */
    INIT_CRC32C(crc);
    COMP_CRC32C(crc,
                ControlFile,
                offsetof(ControlFileData, crc));
    FIN_CRC32C(crc);
 
    *crc_ok_p = EQ_CRC32C(crc, ControlFile->crc);
 
#ifdef FRONTEND
 
    /*
     * If the server was writing at the same time, it is possible that we read
     * partially updated contents on some systems.  If the CRC doesn't match,
     * retry a limited number of times until we compute the same bad CRC twice
     * in a row with a short sleep in between.  Then the failure is unlikely
     * to be due to a concurrent write.
     */
    if (!*crc_ok_p &&
        (retries == 0 || !EQ_CRC32C(crc, last_crc)) &&
        retries < 10)
    {
        retries++;
        last_crc = crc;
        pg_usleep(10000);
        goto retry;
    }
#endif
 
    /* Make sure the control file is valid byte order. */
    if (ControlFile->pg_control_version % 65536 == 0 &&
        ControlFile->pg_control_version / 65536 != 0)
#ifndef FRONTEND
        elog(ERROR, _("byte ordering mismatch"));
#else
        pg_log_warning("possible byte ordering mismatch\n"
                       "The byte ordering used to store the pg_control file might not match the one\n"
                       "used by this program.  In that case the results below would be incorrect, and\n"
                       "the PostgreSQL installation would be incompatible with this data directory.");
#endif
 
    return ControlFile;
}
 
/*
 * update_controlfile()
 *
 * Update controlfile values with the contents given by caller.  The
 * contents to write are included in "ControlFile". "do_sync" can be
 * optionally used to flush the updated control file.  Note that it is up
 * to the caller to properly lock ControlFileLock when calling this
 * routine in the backend.
 */
void
update_controlfile(const char *DataDir,
                   ControlFileData *ControlFile, bool do_sync)
{
    int         fd;
    char        buffer[PG_CONTROL_FILE_SIZE];
    char        ControlFilePath[MAXPGPATH];
 
    /* Update timestamp  */
    ControlFile->time = (pg_time_t) time(NULL);
 
    /* Recalculate CRC of control file */
    INIT_CRC32C(ControlFile->crc);
    COMP_CRC32C(ControlFile->crc,
                ControlFile,
                offsetof(ControlFileData, crc));
    FIN_CRC32C(ControlFile->crc);
 
    /*
     * Write out PG_CONTROL_FILE_SIZE bytes into pg_control by zero-padding
     * the excess over sizeof(ControlFileData), to avoid premature EOF related
     * errors when reading it.
     */
    memset(buffer, 0, PG_CONTROL_FILE_SIZE);
    memcpy(buffer, ControlFile, sizeof(ControlFileData));
 
    snprintf(ControlFilePath, sizeof(ControlFilePath), "%s/%s", DataDir, XLOG_CONTROL_FILE);
 
#ifndef FRONTEND
 
    /*
     * All errors issue a PANIC, so no need to use OpenTransientFile() and to
     * worry about file descriptor leaks.
     */
    if ((fd = BasicOpenFile(ControlFilePath, O_RDWR | PG_BINARY)) < 0)
        ereport(PANIC,
                (errcode_for_file_access(),
                 errmsg("could not open file \"%s\": %m",
                        ControlFilePath)));
#else
    if ((fd = open(ControlFilePath, O_WRONLY | PG_BINARY,
                   pg_file_create_mode)) == -1)
        pg_fatal("could not open file \"%s\": %m", ControlFilePath);
#endif
 
    errno = 0;
#ifndef FRONTEND
    pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_WRITE_UPDATE);
#endif
    if (write(fd, buffer, PG_CONTROL_FILE_SIZE) != PG_CONTROL_FILE_SIZE)
    {
        /* if write didn't set errno, assume problem is no disk space */
        if (errno == 0)
            errno = ENOSPC;
 
#ifndef FRONTEND
        ereport(PANIC,
                (errcode_for_file_access(),
                 errmsg("could not write file \"%s\": %m",
                        ControlFilePath)));
#else
        pg_fatal("could not write file \"%s\": %m", ControlFilePath);
#endif
    }
#ifndef FRONTEND
    pgstat_report_wait_end();
#endif
 
    if (do_sync)
    {
#ifndef FRONTEND
        pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_SYNC_UPDATE);
        if (pg_fsync(fd) != 0)
            ereport(PANIC,
                    (errcode_for_file_access(),
                     errmsg("could not fsync file \"%s\": %m",
                            ControlFilePath)));
        pgstat_report_wait_end();
#else
        if (fsync(fd) != 0)
            pg_fatal("could not fsync file \"%s\": %m", ControlFilePath);
#endif
    }
 
    if (close(fd) != 0)
    {
#ifndef FRONTEND
        ereport(PANIC,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m",
                        ControlFilePath)));
#else
        pg_fatal("could not close file \"%s\": %m", ControlFilePath);
#endif
    }
}