launch_backend.c

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/*-------------------------------------------------------------------------
 *
 * launch_backend.c
 *    Functions for launching backends and other postmaster child
 *    processes.
 *
 * On Unix systems, a new child process is launched with fork().  It inherits
 * all the global variables and data structures that had been initialized in
 * the postmaster.  After forking, the child process closes the file
 * descriptors that are not needed in the child process, and sets up the
 * mechanism to detect death of the parent postmaster process, etc.  After
 * that, it calls the right Main function depending on the kind of child
 * process.
 *
 * In EXEC_BACKEND mode, which is used on Windows but can be enabled on other
 * platforms for testing, the child process is launched by fork() + exec() (or
 * CreateProcess() on Windows).  It does not inherit the state from the
 * postmaster, so it needs to re-attach to the shared memory, re-initialize
 * global variables, reload the config file etc. to get the process to the
 * same state as after fork() on a Unix system.
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/postmaster/launch_backend.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <unistd.h>
 
#include "libpq/libpq-be.h"
#include "miscadmin.h"
#include "postmaster/autovacuum.h"
#include "postmaster/bgworker_internals.h"
#include "postmaster/bgwriter.h"
#include "postmaster/fork_process.h"
#include "postmaster/pgarch.h"
#include "postmaster/postmaster.h"
#include "postmaster/startup.h"
#include "postmaster/syslogger.h"
#include "postmaster/walsummarizer.h"
#include "postmaster/walwriter.h"
#include "replication/slotsync.h"
#include "replication/walreceiver.h"
#include "storage/dsm.h"
#include "storage/io_worker.h"
#include "storage/pg_shmem.h"
#include "tcop/backend_startup.h"
#include "utils/memutils.h"
 
#ifdef EXEC_BACKEND
#include "nodes/queryjumble.h"
#include "storage/pg_shmem.h"
#include "storage/spin.h"
#endif
 
 
#ifdef EXEC_BACKEND
 
#include "common/file_utils.h"
#include "storage/fd.h"
#include "storage/lwlock.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
#include "tcop/tcopprot.h"
#include "utils/injection_point.h"
 
/* Type for a socket that can be inherited to a client process */
#ifdef WIN32
typedef struct
{
    SOCKET      origsocket;     /* Original socket value, or PGINVALID_SOCKET
                                 * if not a socket */
    WSAPROTOCOL_INFO wsainfo;
} InheritableSocket;
#else
typedef int InheritableSocket;
#endif
 
/*
 * Structure contains all variables passed to exec:ed backends
 */
typedef struct
{
    char        DataDir[MAXPGPATH];
#ifndef WIN32
    unsigned long UsedShmemSegID;
#else
    void       *ShmemProtectiveRegion;
    HANDLE      UsedShmemSegID;
#endif
    void       *UsedShmemSegAddr;
    slock_t    *ShmemLock;
#ifdef USE_INJECTION_POINTS
    struct InjectionPointsCtl *ActiveInjectionPoints;
#endif
    int         NamedLWLockTrancheRequests;
    NamedLWLockTranche *NamedLWLockTrancheArray;
    LWLockPadded *MainLWLockArray;
    slock_t    *ProcStructLock;
    PROC_HDR   *ProcGlobal;
    PGPROC     *AuxiliaryProcs;
    PGPROC     *PreparedXactProcs;
    volatile PMSignalData *PMSignalState;
    ProcSignalHeader *ProcSignal;
    pid_t       PostmasterPid;
    TimestampTz PgStartTime;
    TimestampTz PgReloadTime;
    pg_time_t   first_syslogger_file_time;
    bool        redirection_done;
    bool        IsBinaryUpgrade;
    bool        query_id_enabled;
    int         max_safe_fds;
    int         MaxBackends;
    int         num_pmchild_slots;
#ifdef WIN32
    HANDLE      PostmasterHandle;
    HANDLE      initial_signal_pipe;
    HANDLE      syslogPipe[2];
#else
    int         postmaster_alive_fds[2];
    int         syslogPipe[2];
#endif
    char        my_exec_path[MAXPGPATH];
    char        pkglib_path[MAXPGPATH];
 
    int         MyPMChildSlot;
 
    /*
     * These are only used by backend processes, but are here because passing
     * a socket needs some special handling on Windows. 'client_sock' is an
     * explicit argument to postmaster_child_launch, but is stored in
     * MyClientSocket in the child process.
     */
    ClientSocket client_sock;
    InheritableSocket inh_sock;
 
    /*
     * Extra startup data, content depends on the child process.
     */
    size_t      startup_data_len;
    char        startup_data[FLEXIBLE_ARRAY_MEMBER];
} BackendParameters;
 
#define SizeOfBackendParameters(startup_data_len) (offsetof(BackendParameters, startup_data) + startup_data_len)
 
static void read_backend_variables(char *id, void **startup_data, size_t *startup_data_len);
static void restore_backend_variables(BackendParameters *param);
 
static bool save_backend_variables(BackendParameters *param, int child_slot,
                                   ClientSocket *client_sock,
#ifdef WIN32
                                   HANDLE childProcess, pid_t childPid,
#endif
                                   const void *startup_data, size_t startup_data_len);
 
static pid_t internal_forkexec(const char *child_kind, int child_slot,
                               const void *startup_data, size_t startup_data_len,
                               ClientSocket *client_sock);
 
#endif                          /* EXEC_BACKEND */
 
/*
 * Information needed to launch different kinds of child processes.
 */
typedef struct
{
    const char *name;
    void        (*main_fn) (const void *startup_data, size_t startup_data_len);
    bool        shmem_attach;
} child_process_kind;
 
static child_process_kind child_process_kinds[] = {
    [B_INVALID] = {"invalid", NULL, false},
 
    [B_BACKEND] = {"backend", BackendMain, true},
    [B_DEAD_END_BACKEND] = {"dead-end backend", BackendMain, true},
    [B_AUTOVAC_LAUNCHER] = {"autovacuum launcher", AutoVacLauncherMain, true},
    [B_AUTOVAC_WORKER] = {"autovacuum worker", AutoVacWorkerMain, true},
    [B_BG_WORKER] = {"bgworker", BackgroundWorkerMain, true},
 
    /*
     * WAL senders start their life as regular backend processes, and change
     * their type after authenticating the client for replication.  We list it
     * here for PostmasterChildName() but cannot launch them directly.
     */
    [B_WAL_SENDER] = {"wal sender", NULL, true},
    [B_SLOTSYNC_WORKER] = {"slot sync worker", ReplSlotSyncWorkerMain, true},
 
    [B_STANDALONE_BACKEND] = {"standalone backend", NULL, false},
 
    [B_ARCHIVER] = {"archiver", PgArchiverMain, true},
    [B_BG_WRITER] = {"bgwriter", BackgroundWriterMain, true},
    [B_CHECKPOINTER] = {"checkpointer", CheckpointerMain, true},
    [B_IO_WORKER] = {"io_worker", IoWorkerMain, true},
    [B_STARTUP] = {"startup", StartupProcessMain, true},
    [B_WAL_RECEIVER] = {"wal_receiver", WalReceiverMain, true},
    [B_WAL_SUMMARIZER] = {"wal_summarizer", WalSummarizerMain, true},
    [B_WAL_WRITER] = {"wal_writer", WalWriterMain, true},
 
    [B_LOGGER] = {"syslogger", SysLoggerMain, false},
};
 
const char *
PostmasterChildName(BackendType child_type)
{
    return child_process_kinds[child_type].name;
}
 
/*
 * Start a new postmaster child process.
 *
 * The child process will be restored to roughly the same state whether
 * EXEC_BACKEND is used or not: it will be attached to shared memory if
 * appropriate, and fds and other resources that we've inherited from
 * postmaster that are not needed in a child process have been closed.
 *
 * 'child_slot' is the PMChildFlags array index reserved for the child
 * process.  'startup_data' is an optional contiguous chunk of data that is
 * passed to the child process.
 */
pid_t
postmaster_child_launch(BackendType child_type, int child_slot,
                        const void *startup_data, size_t startup_data_len,
                        ClientSocket *client_sock)
{
    pid_t       pid;
 
    Assert(IsPostmasterEnvironment && !IsUnderPostmaster);
 
    /* Capture time Postmaster initiates process creation for logging */
    if (IsExternalConnectionBackend(child_type))
        ((BackendStartupData *) startup_data)->fork_started = GetCurrentTimestamp();
 
#ifdef EXEC_BACKEND
    pid = internal_forkexec(child_process_kinds[child_type].name, child_slot,
                            startup_data, startup_data_len, client_sock);
    /* the child process will arrive in SubPostmasterMain */
#else                           /* !EXEC_BACKEND */
    pid = fork_process();
    if (pid == 0)               /* child */
    {
        /* Capture and transfer timings that may be needed for logging */
        if (IsExternalConnectionBackend(child_type))
        {
            conn_timing.socket_create =
                ((BackendStartupData *) startup_data)->socket_created;
            conn_timing.fork_start =
                ((BackendStartupData *) startup_data)->fork_started;
            conn_timing.fork_end = GetCurrentTimestamp();
        }
 
        /* Close the postmaster's sockets */
        ClosePostmasterPorts(child_type == B_LOGGER);
 
        /* Detangle from postmaster */
        InitPostmasterChild();
 
        /* Detach shared memory if not needed. */
        if (!child_process_kinds[child_type].shmem_attach)
        {
            dsm_detach_all();
            PGSharedMemoryDetach();
        }
 
        /*
         * Enter the Main function with TopMemoryContext.  The startup data is
         * allocated in PostmasterContext, so we cannot release it here yet.
         * The Main function will do it after it's done handling the startup
         * data.
         */
        MemoryContextSwitchTo(TopMemoryContext);
 
        MyPMChildSlot = child_slot;
        if (client_sock)
        {
            MyClientSocket = palloc(sizeof(ClientSocket));
            memcpy(MyClientSocket, client_sock, sizeof(ClientSocket));
        }
 
        /*
         * Run the appropriate Main function
         */
        child_process_kinds[child_type].main_fn(startup_data, startup_data_len);
        pg_unreachable();       /* main_fn never returns */
    }
#endif                          /* EXEC_BACKEND */
    return pid;
}
 
#ifdef EXEC_BACKEND
#ifndef WIN32
 
/*
 * internal_forkexec non-win32 implementation
 *
 * - writes out backend variables to the parameter file
 * - fork():s, and then exec():s the child process
 */
static pid_t
internal_forkexec(const char *child_kind, int child_slot,
                  const void *startup_data, size_t startup_data_len, ClientSocket *client_sock)
{
    static unsigned long tmpBackendFileNum = 0;
    pid_t       pid;
    char        tmpfilename[MAXPGPATH];
    size_t      paramsz;
    BackendParameters *param;
    FILE       *fp;
    char       *argv[4];
    char        forkav[MAXPGPATH];
 
    /*
     * Use palloc0 to make sure padding bytes are initialized, to prevent
     * Valgrind from complaining about writing uninitialized bytes to the
     * file.  This isn't performance critical, and the win32 implementation
     * initializes the padding bytes to zeros, so do it even when not using
     * Valgrind.
     */
    paramsz = SizeOfBackendParameters(startup_data_len);
    param = palloc0(paramsz);
    if (!save_backend_variables(param, child_slot, client_sock, startup_data, startup_data_len))
    {
        pfree(param);
        return -1;              /* log made by save_backend_variables */
    }
 
    /* Calculate name for temp file */
    snprintf(tmpfilename, MAXPGPATH, "%s/%s.backend_var.%d.%lu",
             PG_TEMP_FILES_DIR, PG_TEMP_FILE_PREFIX,
             MyProcPid, ++tmpBackendFileNum);
 
    /* Open file */
    fp = AllocateFile(tmpfilename, PG_BINARY_W);
    if (!fp)
    {
        /*
         * As in OpenTemporaryFileInTablespace, try to make the temp-file
         * directory, ignoring errors.
         */
        (void) MakePGDirectory(PG_TEMP_FILES_DIR);
 
        fp = AllocateFile(tmpfilename, PG_BINARY_W);
        if (!fp)
        {
            ereport(LOG,
                    (errcode_for_file_access(),
                     errmsg("could not create file \"%s\": %m",
                            tmpfilename)));
            pfree(param);
            return -1;
        }
    }
 
    if (fwrite(param, paramsz, 1, fp) != 1)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m", tmpfilename)));
        FreeFile(fp);
        pfree(param);
        return -1;
    }
    pfree(param);
 
    /* Release file */
    if (FreeFile(fp))
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m", tmpfilename)));
        return -1;
    }
 
    /* set up argv properly */
    argv[0] = "postgres";
    snprintf(forkav, MAXPGPATH, "--forkchild=%s", child_kind);
    argv[1] = forkav;
    /* Insert temp file name after --forkchild argument */
    argv[2] = tmpfilename;
    argv[3] = NULL;
 
    /* Fire off execv in child */
    if ((pid = fork_process()) == 0)
    {
        if (execv(postgres_exec_path, argv) < 0)
        {
            ereport(LOG,
                    (errmsg("could not execute server process \"%s\": %m",
                            postgres_exec_path)));
            /* We're already in the child process here, can't return */
            exit(1);
        }
    }
 
    return pid;                 /* Parent returns pid, or -1 on fork failure */
}
#else                           /* WIN32 */
 
/*
 * internal_forkexec win32 implementation
 *
 * - starts backend using CreateProcess(), in suspended state
 * - writes out backend variables to the parameter file
 *  - during this, duplicates handles and sockets required for
 *    inheritance into the new process
 * - resumes execution of the new process once the backend parameter
 *   file is complete.
 */
static pid_t
internal_forkexec(const char *child_kind, int child_slot,
                  const void *startup_data, size_t startup_data_len, ClientSocket *client_sock)
{
    int         retry_count = 0;
    STARTUPINFO si;
    PROCESS_INFORMATION pi;
    char        cmdLine[MAXPGPATH * 2];
    HANDLE      paramHandle;
    BackendParameters *param;
    SECURITY_ATTRIBUTES sa;
    size_t      paramsz;
    char        paramHandleStr[32];
    int         l;
 
    paramsz = SizeOfBackendParameters(startup_data_len);
 
    /* Resume here if we need to retry */
retry:
 
    /* Set up shared memory for parameter passing */
    ZeroMemory(&sa, sizeof(sa));
    sa.nLength = sizeof(sa);
    sa.bInheritHandle = TRUE;
    paramHandle = CreateFileMapping(INVALID_HANDLE_VALUE,
                                    &sa,
                                    PAGE_READWRITE,
                                    0,
                                    paramsz,
                                    NULL);
    if (paramHandle == INVALID_HANDLE_VALUE)
    {
        ereport(LOG,
                (errmsg("could not create backend parameter file mapping: error code %lu",
                        GetLastError())));
        return -1;
    }
    param = MapViewOfFile(paramHandle, FILE_MAP_WRITE, 0, 0, paramsz);
    if (!param)
    {
        ereport(LOG,
                (errmsg("could not map backend parameter memory: error code %lu",
                        GetLastError())));
        CloseHandle(paramHandle);
        return -1;
    }
 
    /* Format the cmd line */
#ifdef _WIN64
    sprintf(paramHandleStr, "%llu", (LONG_PTR) paramHandle);
#else
    sprintf(paramHandleStr, "%lu", (DWORD) paramHandle);
#endif
    l = snprintf(cmdLine, sizeof(cmdLine) - 1, "\"%s\" --forkchild=\"%s\" %s",
                 postgres_exec_path, child_kind, paramHandleStr);
    if (l >= sizeof(cmdLine))
    {
        ereport(LOG,
                (errmsg("subprocess command line too long")));
        UnmapViewOfFile(param);
        CloseHandle(paramHandle);
        return -1;
    }
 
    memset(&pi, 0, sizeof(pi));
    memset(&si, 0, sizeof(si));
    si.cb = sizeof(si);
 
    /*
     * Create the subprocess in a suspended state. This will be resumed later,
     * once we have written out the parameter file.
     */
    if (!CreateProcess(NULL, cmdLine, NULL, NULL, TRUE, CREATE_SUSPENDED,
                       NULL, NULL, &si, &pi))
    {
        ereport(LOG,
                (errmsg("CreateProcess() call failed: %m (error code %lu)",
                        GetLastError())));
        UnmapViewOfFile(param);
        CloseHandle(paramHandle);
        return -1;
    }
 
    if (!save_backend_variables(param, child_slot, client_sock,
                                pi.hProcess, pi.dwProcessId,
                                startup_data, startup_data_len))
    {
        /*
         * log made by save_backend_variables, but we have to clean up the
         * mess with the half-started process
         */
        if (!TerminateProcess(pi.hProcess, 255))
            ereport(LOG,
                    (errmsg_internal("could not terminate unstarted process: error code %lu",
                                     GetLastError())));
        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);
        UnmapViewOfFile(param);
        CloseHandle(paramHandle);
        return -1;              /* log made by save_backend_variables */
    }
 
    /* Drop the parameter shared memory that is now inherited to the backend */
    if (!UnmapViewOfFile(param))
        ereport(LOG,
                (errmsg("could not unmap view of backend parameter file: error code %lu",
                        GetLastError())));
    if (!CloseHandle(paramHandle))
        ereport(LOG,
                (errmsg("could not close handle to backend parameter file: error code %lu",
                        GetLastError())));
 
    /*
     * Reserve the memory region used by our main shared memory segment before
     * we resume the child process.  Normally this should succeed, but if ASLR
     * is active then it might sometimes fail due to the stack or heap having
     * gotten mapped into that range.  In that case, just terminate the
     * process and retry.
     */
    if (!pgwin32_ReserveSharedMemoryRegion(pi.hProcess))
    {
        /* pgwin32_ReserveSharedMemoryRegion already made a log entry */
        if (!TerminateProcess(pi.hProcess, 255))
            ereport(LOG,
                    (errmsg_internal("could not terminate process that failed to reserve memory: error code %lu",
                                     GetLastError())));
        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);
        if (++retry_count < 100)
            goto retry;
        ereport(LOG,
                (errmsg("giving up after too many tries to reserve shared memory"),
                 errhint("This might be caused by ASLR or antivirus software.")));
        return -1;
    }
 
    /*
     * Now that the backend variables are written out, we start the child
     * thread so it can start initializing while we set up the rest of the
     * parent state.
     */
    if (ResumeThread(pi.hThread) == -1)
    {
        if (!TerminateProcess(pi.hProcess, 255))
        {
            ereport(LOG,
                    (errmsg_internal("could not terminate unstartable process: error code %lu",
                                     GetLastError())));
            CloseHandle(pi.hProcess);
            CloseHandle(pi.hThread);
            return -1;
        }
        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);
        ereport(LOG,
                (errmsg_internal("could not resume thread of unstarted process: error code %lu",
                                 GetLastError())));
        return -1;
    }
 
    /* Set up notification when the child process dies */
    pgwin32_register_deadchild_callback(pi.hProcess, pi.dwProcessId);
 
    /* Don't close pi.hProcess, it's owned by the deadchild callback now */
 
    CloseHandle(pi.hThread);
 
    return pi.dwProcessId;
}
#endif                          /* WIN32 */
 
/*
 * SubPostmasterMain -- Get the fork/exec'd process into a state equivalent
 *          to what it would be if we'd simply forked on Unix, and then
 *          dispatch to the appropriate place.
 *
 * The first two command line arguments are expected to be "--forkchild=<name>",
 * where <name> indicates which postmaster child we are to become, and
 * the name of a variables file that we can read to load data that would
 * have been inherited by fork() on Unix.
 */
void
SubPostmasterMain(int argc, char *argv[])
{
    void       *startup_data;
    size_t      startup_data_len;
    char       *child_kind;
    BackendType child_type;
    bool        found = false;
    TimestampTz fork_end;
 
    /* In EXEC_BACKEND case we will not have inherited these settings */
    IsPostmasterEnvironment = true;
    whereToSendOutput = DestNone;
 
    /*
     * Capture the end of process creation for logging. We don't include the
     * time spent copying data from shared memory and setting up the backend.
     */
    fork_end = GetCurrentTimestamp();
 
    /* Setup essential subsystems (to ensure elog() behaves sanely) */
    InitializeGUCOptions();
 
    /* Check we got appropriate args */
    if (argc != 3)
        elog(FATAL, "invalid subpostmaster invocation");
 
    /* Find the entry in child_process_kinds */
    if (strncmp(argv[1], "--forkchild=", 12) != 0)
        elog(FATAL, "invalid subpostmaster invocation (--forkchild argument missing)");
    child_kind = argv[1] + 12;
    found = false;
    for (int idx = 0; idx < lengthof(child_process_kinds); idx++)
    {
        if (strcmp(child_process_kinds[idx].name, child_kind) == 0)
        {
            child_type = (BackendType) idx;
            found = true;
            break;
        }
    }
    if (!found)
        elog(ERROR, "unknown child kind %s", child_kind);
 
    /* Read in the variables file */
    read_backend_variables(argv[2], &startup_data, &startup_data_len);
 
    /* Close the postmaster's sockets (as soon as we know them) */
    ClosePostmasterPorts(child_type == B_LOGGER);
 
    /* Setup as postmaster child */
    InitPostmasterChild();
 
    /*
     * If appropriate, physically re-attach to shared memory segment. We want
     * to do this before going any further to ensure that we can attach at the
     * same address the postmaster used.  On the other hand, if we choose not
     * to re-attach, we may have other cleanup to do.
     *
     * If testing EXEC_BACKEND on Linux, you should run this as root before
     * starting the postmaster:
     *
     * sysctl -w kernel.randomize_va_space=0
     *
     * This prevents using randomized stack and code addresses that cause the
     * child process's memory map to be different from the parent's, making it
     * sometimes impossible to attach to shared memory at the desired address.
     * Return the setting to its old value (usually '1' or '2') when finished.
     */
    if (child_process_kinds[child_type].shmem_attach)
        PGSharedMemoryReAttach();
    else
        PGSharedMemoryNoReAttach();
 
    /* Read in remaining GUC variables */
    read_nondefault_variables();
 
    /* Capture and transfer timings that may be needed for log_connections */
    if (IsExternalConnectionBackend(child_type))
    {
        conn_timing.socket_create =
            ((BackendStartupData *) startup_data)->socket_created;
        conn_timing.fork_start =
            ((BackendStartupData *) startup_data)->fork_started;
        conn_timing.fork_end = fork_end;
    }
 
    /*
     * Check that the data directory looks valid, which will also check the
     * privileges on the data directory and update our umask and file/group
     * variables for creating files later.  Note: this should really be done
     * before we create any files or directories.
     */
    checkDataDir();
 
    /*
     * (re-)read control file, as it contains config. The postmaster will
     * already have read this, but this process doesn't know about that.
     */
    LocalProcessControlFile(false);
 
    /*
     * Reload any libraries that were preloaded by the postmaster.  Since we
     * exec'd this process, those libraries didn't come along with us; but we
     * should load them into all child processes to be consistent with the
     * non-EXEC_BACKEND behavior.
     */
    process_shared_preload_libraries();
 
    /* Restore basic shared memory pointers */
    if (UsedShmemSegAddr != NULL)
        InitShmemAccess(UsedShmemSegAddr);
 
    /*
     * Run the appropriate Main function
     */
    child_process_kinds[child_type].main_fn(startup_data, startup_data_len);
    pg_unreachable();           /* main_fn never returns */
}
 
#ifndef WIN32
#define write_inheritable_socket(dest, src, childpid) ((*(dest) = (src)), true)
#define read_inheritable_socket(dest, src) (*(dest) = *(src))
#else
static bool write_duplicated_handle(HANDLE *dest, HANDLE src, HANDLE child);
static bool write_inheritable_socket(InheritableSocket *dest, SOCKET src,
                                     pid_t childPid);
static void read_inheritable_socket(SOCKET *dest, InheritableSocket *src);
#endif
 
 
/* Save critical backend variables into the BackendParameters struct */
static bool
save_backend_variables(BackendParameters *param,
                       int child_slot, ClientSocket *client_sock,
#ifdef WIN32
                       HANDLE childProcess, pid_t childPid,
#endif
                       const void *startup_data, size_t startup_data_len)
{
    if (client_sock)
        memcpy(&param->client_sock, client_sock, sizeof(ClientSocket));
    else
        memset(&param->client_sock, 0, sizeof(ClientSocket));
    if (!write_inheritable_socket(&param->inh_sock,
                                  client_sock ? client_sock->sock : PGINVALID_SOCKET,
                                  childPid))
        return false;
 
    strlcpy(param->DataDir, DataDir, MAXPGPATH);
 
    param->MyPMChildSlot = child_slot;
 
#ifdef WIN32
    param->ShmemProtectiveRegion = ShmemProtectiveRegion;
#endif
    param->UsedShmemSegID = UsedShmemSegID;
    param->UsedShmemSegAddr = UsedShmemSegAddr;
 
    param->ShmemLock = ShmemLock;
 
#ifdef USE_INJECTION_POINTS
    param->ActiveInjectionPoints = ActiveInjectionPoints;
#endif
 
    param->NamedLWLockTrancheRequests = NamedLWLockTrancheRequests;
    param->NamedLWLockTrancheArray = NamedLWLockTrancheArray;
    param->MainLWLockArray = MainLWLockArray;
    param->ProcStructLock = ProcStructLock;
    param->ProcGlobal = ProcGlobal;
    param->AuxiliaryProcs = AuxiliaryProcs;
    param->PreparedXactProcs = PreparedXactProcs;
    param->PMSignalState = PMSignalState;
    param->ProcSignal = ProcSignal;
 
    param->PostmasterPid = PostmasterPid;
    param->PgStartTime = PgStartTime;
    param->PgReloadTime = PgReloadTime;
    param->first_syslogger_file_time = first_syslogger_file_time;
 
    param->redirection_done = redirection_done;
    param->IsBinaryUpgrade = IsBinaryUpgrade;
    param->query_id_enabled = query_id_enabled;
    param->max_safe_fds = max_safe_fds;
 
    param->MaxBackends = MaxBackends;
    param->num_pmchild_slots = num_pmchild_slots;
 
#ifdef WIN32
    param->PostmasterHandle = PostmasterHandle;
    if (!write_duplicated_handle(&param->initial_signal_pipe,
                                 pgwin32_create_signal_listener(childPid),
                                 childProcess))
        return false;
#else
    memcpy(&param->postmaster_alive_fds, &postmaster_alive_fds,
           sizeof(postmaster_alive_fds));
#endif
 
    memcpy(&param->syslogPipe, &syslogPipe, sizeof(syslogPipe));
 
    strlcpy(param->my_exec_path, my_exec_path, MAXPGPATH);
 
    strlcpy(param->pkglib_path, pkglib_path, MAXPGPATH);
 
    param->startup_data_len = startup_data_len;
    if (startup_data_len > 0)
        memcpy(param->startup_data, startup_data, startup_data_len);
 
    return true;
}
 
#ifdef WIN32
/*
 * Duplicate a handle for usage in a child process, and write the child
 * process instance of the handle to the parameter file.
 */
static bool
write_duplicated_handle(HANDLE *dest, HANDLE src, HANDLE childProcess)
{
    HANDLE      hChild = INVALID_HANDLE_VALUE;
 
    if (!DuplicateHandle(GetCurrentProcess(),
                         src,
                         childProcess,
                         &hChild,
                         0,
                         TRUE,
                         DUPLICATE_CLOSE_SOURCE | DUPLICATE_SAME_ACCESS))
    {
        ereport(LOG,
                (errmsg_internal("could not duplicate handle to be written to backend parameter file: error code %lu",
                                 GetLastError())));
        return false;
    }
 
    *dest = hChild;
    return true;
}
 
/*
 * Duplicate a socket for usage in a child process, and write the resulting
 * structure to the parameter file.
 * This is required because a number of LSPs (Layered Service Providers) very
 * common on Windows (antivirus, firewalls, download managers etc) break
 * straight socket inheritance.
 */
static bool
write_inheritable_socket(InheritableSocket *dest, SOCKET src, pid_t childpid)
{
    dest->origsocket = src;
    if (src != 0 && src != PGINVALID_SOCKET)
    {
        /* Actual socket */
        if (WSADuplicateSocket(src, childpid, &dest->wsainfo) != 0)
        {
            ereport(LOG,
                    (errmsg("could not duplicate socket %d for use in backend: error code %d",
                            (int) src, WSAGetLastError())));
            return false;
        }
    }
    return true;
}
 
/*
 * Read a duplicate socket structure back, and get the socket descriptor.
 */
static void
read_inheritable_socket(SOCKET *dest, InheritableSocket *src)
{
    SOCKET      s;
 
    if (src->origsocket == PGINVALID_SOCKET || src->origsocket == 0)
    {
        /* Not a real socket! */
        *dest = src->origsocket;
    }
    else
    {
        /* Actual socket, so create from structure */
        s = WSASocket(FROM_PROTOCOL_INFO,
                      FROM_PROTOCOL_INFO,
                      FROM_PROTOCOL_INFO,
                      &src->wsainfo,
                      0,
                      0);
        if (s == INVALID_SOCKET)
        {
            write_stderr("could not create inherited socket: error code %d\n",
                         WSAGetLastError());
            exit(1);
        }
        *dest = s;
 
        /*
         * To make sure we don't get two references to the same socket, close
         * the original one. (This would happen when inheritance actually
         * works..
         */
        closesocket(src->origsocket);
    }
}
#endif
 
static void
read_backend_variables(char *id, void **startup_data, size_t *startup_data_len)
{
    BackendParameters param;
 
#ifndef WIN32
    /* Non-win32 implementation reads from file */
    FILE       *fp;
 
    /* Open file */
    fp = AllocateFile(id, PG_BINARY_R);
    if (!fp)
    {
        write_stderr("could not open backend variables file \"%s\": %m\n", id);
        exit(1);
    }
 
    if (fread(&param, sizeof(param), 1, fp) != 1)
    {
        write_stderr("could not read from backend variables file \"%s\": %m\n", id);
        exit(1);
    }
 
    /* read startup data */
    *startup_data_len = param.startup_data_len;
    if (param.startup_data_len > 0)
    {
        *startup_data = palloc(*startup_data_len);
        if (fread(*startup_data, *startup_data_len, 1, fp) != 1)
        {
            write_stderr("could not read startup data from backend variables file \"%s\": %m\n",
                         id);
            exit(1);
        }
    }
    else
        *startup_data = NULL;
 
    /* Release file */
    FreeFile(fp);
    if (unlink(id) != 0)
    {
        write_stderr("could not remove file \"%s\": %m\n", id);
        exit(1);
    }
#else
    /* Win32 version uses mapped file */
    HANDLE      paramHandle;
    BackendParameters *paramp;
 
#ifdef _WIN64
    paramHandle = (HANDLE) _atoi64(id);
#else
    paramHandle = (HANDLE) atol(id);
#endif
    paramp = MapViewOfFile(paramHandle, FILE_MAP_READ, 0, 0, 0);
    if (!paramp)
    {
        write_stderr("could not map view of backend variables: error code %lu\n",
                     GetLastError());
        exit(1);
    }
 
    memcpy(&param, paramp, sizeof(BackendParameters));
 
    /* read startup data */
    *startup_data_len = param.startup_data_len;
    if (param.startup_data_len > 0)
    {
        *startup_data = palloc(paramp->startup_data_len);
        memcpy(*startup_data, paramp->startup_data, param.startup_data_len);
    }
    else
        *startup_data = NULL;
 
    if (!UnmapViewOfFile(paramp))
    {
        write_stderr("could not unmap view of backend variables: error code %lu\n",
                     GetLastError());
        exit(1);
    }
 
    if (!CloseHandle(paramHandle))
    {
        write_stderr("could not close handle to backend parameter variables: error code %lu\n",
                     GetLastError());
        exit(1);
    }
#endif
 
    restore_backend_variables(&param);
}
 
/* Restore critical backend variables from the BackendParameters struct */
static void
restore_backend_variables(BackendParameters *param)
{
    if (param->client_sock.sock != PGINVALID_SOCKET)
    {
        MyClientSocket = MemoryContextAlloc(TopMemoryContext, sizeof(ClientSocket));
        memcpy(MyClientSocket, &param->client_sock, sizeof(ClientSocket));
        read_inheritable_socket(&MyClientSocket->sock, &param->inh_sock);
    }
 
    SetDataDir(param->DataDir);
 
    MyPMChildSlot = param->MyPMChildSlot;
 
#ifdef WIN32
    ShmemProtectiveRegion = param->ShmemProtectiveRegion;
#endif
    UsedShmemSegID = param->UsedShmemSegID;
    UsedShmemSegAddr = param->UsedShmemSegAddr;
 
    ShmemLock = param->ShmemLock;
 
#ifdef USE_INJECTION_POINTS
    ActiveInjectionPoints = param->ActiveInjectionPoints;
#endif
 
    NamedLWLockTrancheRequests = param->NamedLWLockTrancheRequests;
    NamedLWLockTrancheArray = param->NamedLWLockTrancheArray;
    MainLWLockArray = param->MainLWLockArray;
    ProcStructLock = param->ProcStructLock;
    ProcGlobal = param->ProcGlobal;
    AuxiliaryProcs = param->AuxiliaryProcs;
    PreparedXactProcs = param->PreparedXactProcs;
    PMSignalState = param->PMSignalState;
    ProcSignal = param->ProcSignal;
 
    PostmasterPid = param->PostmasterPid;
    PgStartTime = param->PgStartTime;
    PgReloadTime = param->PgReloadTime;
    first_syslogger_file_time = param->first_syslogger_file_time;
 
    redirection_done = param->redirection_done;
    IsBinaryUpgrade = param->IsBinaryUpgrade;
    query_id_enabled = param->query_id_enabled;
    max_safe_fds = param->max_safe_fds;
 
    MaxBackends = param->MaxBackends;
    num_pmchild_slots = param->num_pmchild_slots;
 
#ifdef WIN32
    PostmasterHandle = param->PostmasterHandle;
    pgwin32_initial_signal_pipe = param->initial_signal_pipe;
#else
    memcpy(&postmaster_alive_fds, &param->postmaster_alive_fds,
           sizeof(postmaster_alive_fds));
#endif
 
    memcpy(&syslogPipe, &param->syslogPipe, sizeof(syslogPipe));
 
    strlcpy(my_exec_path, param->my_exec_path, MAXPGPATH);
 
    strlcpy(pkglib_path, param->pkglib_path, MAXPGPATH);
 
    /*
     * We need to restore fd.c's counts of externally-opened FDs; to avoid
     * confusion, be sure to do this after restoring max_safe_fds.  (Note:
     * BackendInitialize will handle this for (*client_sock)->sock.)
     */
#ifndef WIN32
    if (postmaster_alive_fds[0] >= 0)
        ReserveExternalFD();
    if (postmaster_alive_fds[1] >= 0)
        ReserveExternalFD();
#endif
}
 
#endif                          /* EXEC_BACKEND */