miscinit.c

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/*-------------------------------------------------------------------------
 *
 * miscinit.c
 *    miscellaneous initialization support stuff
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/init/miscinit.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <sys/param.h>
#include <signal.h>
#include <time.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <fcntl.h>
#include <unistd.h>
#include <grp.h>
#include <pwd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#ifdef HAVE_UTIME_H
#include <utime.h>
#endif

#include "access/htup_details.h"
#include "catalog/pg_authid.h"
#include "libpq/libpq.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#include "postmaster/postmaster.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
#include "utils/varlena.h"


#define DIRECTORY_LOCK_FILE     "postmaster.pid"

ProcessingMode Mode = InitProcessing;

/* List of lock files to be removed at proc exit */
static List *lock_files = NIL;

static Latch LocalLatchData;

/* ----------------------------------------------------------------
 *      ignoring system indexes support stuff
 *
 * NOTE: "ignoring system indexes" means we do not use the system indexes
 * for lookups (either in hardwired catalog accesses or in planner-generated
 * plans).  We do, however, still update the indexes when a catalog
 * modification is made.
 * ----------------------------------------------------------------
 */

bool        IgnoreSystemIndexes = false;


/* ----------------------------------------------------------------
 *              database path / name support stuff
 * ----------------------------------------------------------------
 */

void
SetDatabasePath(const char *path)
{
    /* This should happen only once per process */
    Assert(!DatabasePath);
    DatabasePath = MemoryContextStrdup(TopMemoryContext, path);
}

/*
 * Set data directory, but make sure it's an absolute path.  Use this,
 * never set DataDir directly.
 */
void
SetDataDir(const char *dir)
{
    char       *new;

    AssertArg(dir);

    /* If presented path is relative, convert to absolute */
    new = make_absolute_path(dir);

    if (DataDir)
        free(DataDir);
    DataDir = new;
}

/*
 * Change working directory to DataDir.  Most of the postmaster and backend
 * code assumes that we are in DataDir so it can use relative paths to access
 * stuff in and under the data directory.  For convenience during path
 * setup, however, we don't force the chdir to occur during SetDataDir.
 */
void
ChangeToDataDir(void)
{
    AssertState(DataDir);

    if (chdir(DataDir) < 0)
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg("could not change directory to \"%s\": %m",
                        DataDir)));
}


/* ----------------------------------------------------------------
 *  User ID state
 *
 * We have to track several different values associated with the concept
 * of "user ID".
 *
 * AuthenticatedUserId is determined at connection start and never changes.
 *
 * SessionUserId is initially the same as AuthenticatedUserId, but can be
 * changed by SET SESSION AUTHORIZATION (if AuthenticatedUserIsSuperuser).
 * This is the ID reported by the SESSION_USER SQL function.
 *
 * OuterUserId is the current user ID in effect at the "outer level" (outside
 * any transaction or function).  This is initially the same as SessionUserId,
 * but can be changed by SET ROLE to any role that SessionUserId is a
 * member of.  (XXX rename to something like CurrentRoleId?)
 *
 * CurrentUserId is the current effective user ID; this is the one to use
 * for all normal permissions-checking purposes.  At outer level this will
 * be the same as OuterUserId, but it changes during calls to SECURITY
 * DEFINER functions, as well as locally in some specialized commands.
 *
 * SecurityRestrictionContext holds flags indicating reason(s) for changing
 * CurrentUserId.  In some cases we need to lock down operations that are
 * not directly controlled by privilege settings, and this provides a
 * convenient way to do it.
 * ----------------------------------------------------------------
 */
static Oid  AuthenticatedUserId = InvalidOid;
static Oid  SessionUserId = InvalidOid;
static Oid  OuterUserId = InvalidOid;
static Oid  CurrentUserId = InvalidOid;

/* We also have to remember the superuser state of some of these levels */
static bool AuthenticatedUserIsSuperuser = false;
static bool SessionUserIsSuperuser = false;

static int  SecurityRestrictionContext = 0;

/* We also remember if a SET ROLE is currently active */
static bool SetRoleIsActive = false;

/*
 * Initialize the basic environment for a postmaster child
 *
 * Should be called as early as possible after the child's startup.
 */
void
InitPostmasterChild(void)
{
    IsUnderPostmaster = true;   /* we are a postmaster subprocess now */

    MyProcPid = getpid();       /* reset MyProcPid */

    MyStartTime = time(NULL);   /* set our start time in case we call elog */

    /*
     * make sure stderr is in binary mode before anything can possibly be
     * written to it, in case it's actually the syslogger pipe, so the pipe
     * chunking protocol isn't disturbed. Non-logpipe data gets translated on
     * redirection (e.g. via pg_ctl -l) anyway.
     */
#ifdef WIN32
    _setmode(fileno(stderr), _O_BINARY);
#endif

    /* We don't want the postmaster's proc_exit() handlers */
    on_exit_reset();

    /* Initialize process-local latch support */
    InitializeLatchSupport();
    MyLatch = &LocalLatchData;
    InitLatch(MyLatch);

    /*
     * If possible, make this process a group leader, so that the postmaster
     * can signal any child processes too. Not all processes will have
     * children, but for consistency we make all postmaster child processes do
     * this.
     */
#ifdef HAVE_SETSID
    if (setsid() < 0)
        elog(FATAL, "setsid() failed: %m");
#endif
}

/*
 * Initialize the basic environment for a standalone process.
 *
 * argv0 has to be suitable to find the program's executable.
 */
void
InitStandaloneProcess(const char *argv0)
{
    Assert(!IsPostmasterEnvironment);

    MyProcPid = getpid();       /* reset MyProcPid */

    MyStartTime = time(NULL);   /* set our start time in case we call elog */

    /* Initialize process-local latch support */
    InitializeLatchSupport();
    MyLatch = &LocalLatchData;
    InitLatch(MyLatch);

    /* Compute paths, no postmaster to inherit from */
    if (my_exec_path[0] == '\0')
    {
        if (find_my_exec(argv0, my_exec_path) < 0)
            elog(FATAL, "%s: could not locate my own executable path",
                 argv0);
    }

    if (pkglib_path[0] == '\0')
        get_pkglib_path(my_exec_path, pkglib_path);
}

void
SwitchToSharedLatch(void)
{
    Assert(MyLatch == &LocalLatchData);
    Assert(MyProc != NULL);

    MyLatch = &MyProc->procLatch;

    if (FeBeWaitSet)
        ModifyWaitEvent(FeBeWaitSet, 1, WL_LATCH_SET, MyLatch);

    /*
     * Set the shared latch as the local one might have been set. This
     * shouldn't normally be necessary as code is supposed to check the
     * condition before waiting for the latch, but a bit care can't hurt.
     */
    SetLatch(MyLatch);
}

void
SwitchBackToLocalLatch(void)
{
    Assert(MyLatch != &LocalLatchData);
    Assert(MyProc != NULL && MyLatch == &MyProc->procLatch);

    MyLatch = &LocalLatchData;

    if (FeBeWaitSet)
        ModifyWaitEvent(FeBeWaitSet, 1, WL_LATCH_SET, MyLatch);

    SetLatch(MyLatch);
}

/*
 * GetUserId - get the current effective user ID.
 *
 * Note: there's no SetUserId() anymore; use SetUserIdAndSecContext().
 */
Oid
GetUserId(void)
{
    AssertState(OidIsValid(CurrentUserId));
    return CurrentUserId;
}


/*
 * GetOuterUserId/SetOuterUserId - get/set the outer-level user ID.
 */
Oid
GetOuterUserId(void)
{
    AssertState(OidIsValid(OuterUserId));
    return OuterUserId;
}


static void
SetOuterUserId(Oid userid)
{
    AssertState(SecurityRestrictionContext == 0);
    AssertArg(OidIsValid(userid));
    OuterUserId = userid;

    /* We force the effective user ID to match, too */
    CurrentUserId = userid;
}


/*
 * GetSessionUserId/SetSessionUserId - get/set the session user ID.
 */
Oid
GetSessionUserId(void)
{
    AssertState(OidIsValid(SessionUserId));
    return SessionUserId;
}


static void
SetSessionUserId(Oid userid, bool is_superuser)
{
    AssertState(SecurityRestrictionContext == 0);
    AssertArg(OidIsValid(userid));
    SessionUserId = userid;
    SessionUserIsSuperuser = is_superuser;
    SetRoleIsActive = false;

    /* We force the effective user IDs to match, too */
    OuterUserId = userid;
    CurrentUserId = userid;
}

/*
 * GetAuthenticatedUserId - get the authenticated user ID
 */
Oid
GetAuthenticatedUserId(void)
{
    AssertState(OidIsValid(AuthenticatedUserId));
    return AuthenticatedUserId;
}


/*
 * GetUserIdAndSecContext/SetUserIdAndSecContext - get/set the current user ID
 * and the SecurityRestrictionContext flags.
 *
 * Currently there are three valid bits in SecurityRestrictionContext:
 *
 * SECURITY_LOCAL_USERID_CHANGE indicates that we are inside an operation
 * that is temporarily changing CurrentUserId via these functions.  This is
 * needed to indicate that the actual value of CurrentUserId is not in sync
 * with guc.c's internal state, so SET ROLE has to be disallowed.
 *
 * SECURITY_RESTRICTED_OPERATION indicates that we are inside an operation
 * that does not wish to trust called user-defined functions at all.  This
 * bit prevents not only SET ROLE, but various other changes of session state
 * that normally is unprotected but might possibly be used to subvert the
 * calling session later.  An example is replacing an existing prepared
 * statement with new code, which will then be executed with the outer
 * session's permissions when the prepared statement is next used.  Since
 * these restrictions are fairly draconian, we apply them only in contexts
 * where the called functions are really supposed to be side-effect-free
 * anyway, such as VACUUM/ANALYZE/REINDEX.
 *
 * SECURITY_NOFORCE_RLS indicates that we are inside an operation which should
 * ignore the FORCE ROW LEVEL SECURITY per-table indication.  This is used to
 * ensure that FORCE RLS does not mistakenly break referential integrity
 * checks.  Note that this is intentionally only checked when running as the
 * owner of the table (which should always be the case for referential
 * integrity checks).
 *
 * Unlike GetUserId, GetUserIdAndSecContext does *not* Assert that the current
 * value of CurrentUserId is valid; nor does SetUserIdAndSecContext require
 * the new value to be valid.  In fact, these routines had better not
 * ever throw any kind of error.  This is because they are used by
 * StartTransaction and AbortTransaction to save/restore the settings,
 * and during the first transaction within a backend, the value to be saved
 * and perhaps restored is indeed invalid.  We have to be able to get
 * through AbortTransaction without asserting in case InitPostgres fails.
 */
void
GetUserIdAndSecContext(Oid *userid, int *sec_context)
{
    *userid = CurrentUserId;
    *sec_context = SecurityRestrictionContext;
}

void
SetUserIdAndSecContext(Oid userid, int sec_context)
{
    CurrentUserId = userid;
    SecurityRestrictionContext = sec_context;
}


/*
 * InLocalUserIdChange - are we inside a local change of CurrentUserId?
 */
bool
InLocalUserIdChange(void)
{
    return (SecurityRestrictionContext & SECURITY_LOCAL_USERID_CHANGE) != 0;
}

/*
 * InSecurityRestrictedOperation - are we inside a security-restricted command?
 */
bool
InSecurityRestrictedOperation(void)
{
    return (SecurityRestrictionContext & SECURITY_RESTRICTED_OPERATION) != 0;
}

/*
 * InNoForceRLSOperation - are we ignoring FORCE ROW LEVEL SECURITY ?
 */
bool
InNoForceRLSOperation(void)
{
    return (SecurityRestrictionContext & SECURITY_NOFORCE_RLS) != 0;
}


/*
 * These are obsolete versions of Get/SetUserIdAndSecContext that are
 * only provided for bug-compatibility with some rather dubious code in
 * pljava.  We allow the userid to be set, but only when not inside a
 * security restriction context.
 */
void
GetUserIdAndContext(Oid *userid, bool *sec_def_context)
{
    *userid = CurrentUserId;
    *sec_def_context = InLocalUserIdChange();
}

void
SetUserIdAndContext(Oid userid, bool sec_def_context)
{
    /* We throw the same error SET ROLE would. */
    if (InSecurityRestrictedOperation())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("cannot set parameter \"%s\" within security-restricted operation",
                        "role")));
    CurrentUserId = userid;
    if (sec_def_context)
        SecurityRestrictionContext |= SECURITY_LOCAL_USERID_CHANGE;
    else
        SecurityRestrictionContext &= ~SECURITY_LOCAL_USERID_CHANGE;
}


/*
 * Check whether specified role has explicit REPLICATION privilege
 */
bool
has_rolreplication(Oid roleid)
{
    bool        result = false;
    HeapTuple   utup;

    utup = SearchSysCache1(AUTHOID, ObjectIdGetDatum(roleid));
    if (HeapTupleIsValid(utup))
    {
        result = ((Form_pg_authid) GETSTRUCT(utup))->rolreplication;
        ReleaseSysCache(utup);
    }
    return result;
}

/*
 * Initialize user identity during normal backend startup
 */
void
InitializeSessionUserId(const char *rolename, Oid roleid)
{
    HeapTuple   roleTup;
    Form_pg_authid rform;
    char       *rname;

    /*
     * Don't do scans if we're bootstrapping, none of the system catalogs
     * exist yet, and they should be owned by postgres anyway.
     */
    AssertState(!IsBootstrapProcessingMode());

    /* call only once */
    AssertState(!OidIsValid(AuthenticatedUserId));

    if (rolename != NULL)
    {
        roleTup = SearchSysCache1(AUTHNAME, PointerGetDatum(rolename));
        if (!HeapTupleIsValid(roleTup))
            ereport(FATAL,
                    (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                     errmsg("role \"%s\" does not exist", rolename)));
    }
    else
    {
        roleTup = SearchSysCache1(AUTHOID, ObjectIdGetDatum(roleid));
        if (!HeapTupleIsValid(roleTup))
            ereport(FATAL,
                    (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                     errmsg("role with OID %u does not exist", roleid)));
    }

    rform = (Form_pg_authid) GETSTRUCT(roleTup);
    roleid = HeapTupleGetOid(roleTup);
    rname = NameStr(rform->rolname);

    AuthenticatedUserId = roleid;
    AuthenticatedUserIsSuperuser = rform->rolsuper;

    /* This sets OuterUserId/CurrentUserId too */
    SetSessionUserId(roleid, AuthenticatedUserIsSuperuser);

    /* Also mark our PGPROC entry with the authenticated user id */
    /* (We assume this is an atomic store so no lock is needed) */
    MyProc->roleId = roleid;

    /*
     * These next checks are not enforced when in standalone mode, so that
     * there is a way to recover from sillinesses like "UPDATE pg_authid SET
     * rolcanlogin = false;".
     */
    if (IsUnderPostmaster)
    {
        /*
         * Is role allowed to login at all?
         */
        if (!rform->rolcanlogin)
            ereport(FATAL,
                    (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                     errmsg("role \"%s\" is not permitted to log in",
                            rname)));

        /*
         * Check connection limit for this role.
         *
         * There is a race condition here --- we create our PGPROC before
         * checking for other PGPROCs.  If two backends did this at about the
         * same time, they might both think they were over the limit, while
         * ideally one should succeed and one fail.  Getting that to work
         * exactly seems more trouble than it is worth, however; instead we
         * just document that the connection limit is approximate.
         */
        if (rform->rolconnlimit >= 0 &&
            !AuthenticatedUserIsSuperuser &&
            CountUserBackends(roleid) > rform->rolconnlimit)
            ereport(FATAL,
                    (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                     errmsg("too many connections for role \"%s\"",
                            rname)));
    }

    /* Record username and superuser status as GUC settings too */
    SetConfigOption("session_authorization", rname,
                    PGC_BACKEND, PGC_S_OVERRIDE);
    SetConfigOption("is_superuser",
                    AuthenticatedUserIsSuperuser ? "on" : "off",
                    PGC_INTERNAL, PGC_S_OVERRIDE);

    ReleaseSysCache(roleTup);
}


/*
 * Initialize user identity during special backend startup
 */
void
InitializeSessionUserIdStandalone(void)
{
    /*
     * This function should only be called in single-user mode, in autovacuum
     * workers, and in background workers.
     */
    AssertState(!IsUnderPostmaster || IsAutoVacuumWorkerProcess() || IsBackgroundWorker);

    /* call only once */
    AssertState(!OidIsValid(AuthenticatedUserId));

    AuthenticatedUserId = BOOTSTRAP_SUPERUSERID;
    AuthenticatedUserIsSuperuser = true;

    SetSessionUserId(BOOTSTRAP_SUPERUSERID, true);
}


/*
 * Change session auth ID while running
 *
 * Only a superuser may set auth ID to something other than himself.  Note
 * that in case of multiple SETs in a single session, the original userid's
 * superuserness is what matters.  But we set the GUC variable is_superuser
 * to indicate whether the *current* session userid is a superuser.
 *
 * Note: this is not an especially clean place to do the permission check.
 * It's OK because the check does not require catalog access and can't
 * fail during an end-of-transaction GUC reversion, but we may someday
 * have to push it up into assign_session_authorization.
 */
void
SetSessionAuthorization(Oid userid, bool is_superuser)
{
    /* Must have authenticated already, else can't make permission check */
    AssertState(OidIsValid(AuthenticatedUserId));

    if (userid != AuthenticatedUserId &&
        !AuthenticatedUserIsSuperuser)
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied to set session authorization")));

    SetSessionUserId(userid, is_superuser);

    SetConfigOption("is_superuser",
                    is_superuser ? "on" : "off",
                    PGC_INTERNAL, PGC_S_OVERRIDE);
}

/*
 * Report current role id
 *      This follows the semantics of SET ROLE, ie return the outer-level ID
 *      not the current effective ID, and return InvalidOid when the setting
 *      is logically SET ROLE NONE.
 */
Oid
GetCurrentRoleId(void)
{
    if (SetRoleIsActive)
        return OuterUserId;
    else
        return InvalidOid;
}

/*
 * Change Role ID while running (SET ROLE)
 *
 * If roleid is InvalidOid, we are doing SET ROLE NONE: revert to the
 * session user authorization.  In this case the is_superuser argument
 * is ignored.
 *
 * When roleid is not InvalidOid, the caller must have checked whether
 * the session user has permission to become that role.  (We cannot check
 * here because this routine must be able to execute in a failed transaction
 * to restore a prior value of the ROLE GUC variable.)
 */
void
SetCurrentRoleId(Oid roleid, bool is_superuser)
{
    /*
     * Get correct info if it's SET ROLE NONE
     *
     * If SessionUserId hasn't been set yet, just do nothing --- the eventual
     * SetSessionUserId call will fix everything.  This is needed since we
     * will get called during GUC initialization.
     */
    if (!OidIsValid(roleid))
    {
        if (!OidIsValid(SessionUserId))
            return;

        roleid = SessionUserId;
        is_superuser = SessionUserIsSuperuser;

        SetRoleIsActive = false;
    }
    else
        SetRoleIsActive = true;

    SetOuterUserId(roleid);

    SetConfigOption("is_superuser",
                    is_superuser ? "on" : "off",
                    PGC_INTERNAL, PGC_S_OVERRIDE);
}


/*
 * Get user name from user oid, returns NULL for nonexistent roleid if noerr
 * is true.
 */
char *
GetUserNameFromId(Oid roleid, bool noerr)
{
    HeapTuple   tuple;
    char       *result;

    tuple = SearchSysCache1(AUTHOID, ObjectIdGetDatum(roleid));
    if (!HeapTupleIsValid(tuple))
    {
        if (!noerr)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("invalid role OID: %u", roleid)));
        result = NULL;
    }
    else
    {
        result = pstrdup(NameStr(((Form_pg_authid) GETSTRUCT(tuple))->rolname));
        ReleaseSysCache(tuple);
    }
    return result;
}


/*-------------------------------------------------------------------------
 *              Interlock-file support
 *
 * These routines are used to create both a data-directory lockfile
 * ($DATADIR/postmaster.pid) and Unix-socket-file lockfiles ($SOCKFILE.lock).
 * Both kinds of files contain the same info initially, although we can add
 * more information to a data-directory lockfile after it's created, using
 * AddToDataDirLockFile().  See miscadmin.h for documentation of the contents
 * of these lockfiles.
 *
 * On successful lockfile creation, a proc_exit callback to remove the
 * lockfile is automatically created.
 *-------------------------------------------------------------------------
 */

/*
 * proc_exit callback to remove lockfiles.
 */
static void
UnlinkLockFiles(int status, Datum arg)
{
    ListCell   *l;

    foreach(l, lock_files)
    {
        char       *curfile = (char *) lfirst(l);

        unlink(curfile);
        /* Should we complain if the unlink fails? */
    }
    /* Since we're about to exit, no need to reclaim storage */
    lock_files = NIL;

    /*
     * Lock file removal should always be the last externally visible action
     * of a postmaster or standalone backend, while we won't come here at all
     * when exiting postmaster child processes.  Therefore, this is a good
     * place to log completion of shutdown.  We could alternatively teach
     * proc_exit() to do it, but that seems uglier.  In a standalone backend,
     * use NOTICE elevel to be less chatty.
     */
    ereport(IsPostmasterEnvironment ? LOG : NOTICE,
            (errmsg("database system is shut down")));
}

/*
 * Create a lockfile.
 *
 * filename is the path name of the lockfile to create.
 * amPostmaster is used to determine how to encode the output PID.
 * socketDir is the Unix socket directory path to include (possibly empty).
 * isDDLock and refName are used to determine what error message to produce.
 */
static void
CreateLockFile(const char *filename, bool amPostmaster,
               const char *socketDir,
               bool isDDLock, const char *refName)
{
    int         fd;
    char        buffer[MAXPGPATH * 2 + 256];
    int         ntries;
    int         len;
    int         encoded_pid;
    pid_t       other_pid;
    pid_t       my_pid,
                my_p_pid,
                my_gp_pid;
    const char *envvar;

    /*
     * If the PID in the lockfile is our own PID or our parent's or
     * grandparent's PID, then the file must be stale (probably left over from
     * a previous system boot cycle).  We need to check this because of the
     * likelihood that a reboot will assign exactly the same PID as we had in
     * the previous reboot, or one that's only one or two counts larger and
     * hence the lockfile's PID now refers to an ancestor shell process.  We
     * allow pg_ctl to pass down its parent shell PID (our grandparent PID)
     * via the environment variable PG_GRANDPARENT_PID; this is so that
     * launching the postmaster via pg_ctl can be just as reliable as
     * launching it directly.  There is no provision for detecting
     * further-removed ancestor processes, but if the init script is written
     * carefully then all but the immediate parent shell will be root-owned
     * processes and so the kill test will fail with EPERM.  Note that we
     * cannot get a false negative this way, because an existing postmaster
     * would surely never launch a competing postmaster or pg_ctl process
     * directly.
     */
    my_pid = getpid();

#ifndef WIN32
    my_p_pid = getppid();
#else

    /*
     * Windows hasn't got getppid(), but doesn't need it since it's not using
     * real kill() either...
     */
    my_p_pid = 0;
#endif

    envvar = getenv("PG_GRANDPARENT_PID");
    if (envvar)
        my_gp_pid = atoi(envvar);
    else
        my_gp_pid = 0;

    /*
     * We need a loop here because of race conditions.  But don't loop forever
     * (for example, a non-writable $PGDATA directory might cause a failure
     * that won't go away).  100 tries seems like plenty.
     */
    for (ntries = 0;; ntries++)
    {
        /*
         * Try to create the lock file --- O_EXCL makes this atomic.
         *
         * Think not to make the file protection weaker than 0600.  See
         * comments below.
         */
        fd = open(filename, O_RDWR | O_CREAT | O_EXCL, 0600);
        if (fd >= 0)
            break;              /* Success; exit the retry loop */

        /*
         * Couldn't create the pid file. Probably it already exists.
         */
        if ((errno != EEXIST && errno != EACCES) || ntries > 100)
            ereport(FATAL,
                    (errcode_for_file_access(),
                     errmsg("could not create lock file \"%s\": %m",
                            filename)));

        /*
         * Read the file to get the old owner's PID.  Note race condition
         * here: file might have been deleted since we tried to create it.
         */
        fd = open(filename, O_RDONLY, 0600);
        if (fd < 0)
        {
            if (errno == ENOENT)
                continue;       /* race condition; try again */
            ereport(FATAL,
                    (errcode_for_file_access(),
                     errmsg("could not open lock file \"%s\": %m",
                            filename)));
        }
        pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_CREATE_READ);
        if ((len = read(fd, buffer, sizeof(buffer) - 1)) < 0)
            ereport(FATAL,
                    (errcode_for_file_access(),
                     errmsg("could not read lock file \"%s\": %m",
                            filename)));
        pgstat_report_wait_end();
        close(fd);

        if (len == 0)
        {
            ereport(FATAL,
                    (errcode(ERRCODE_LOCK_FILE_EXISTS),
                     errmsg("lock file \"%s\" is empty", filename),
                     errhint("Either another server is starting, or the lock file is the remnant of a previous server startup crash.")));
        }

        buffer[len] = '\0';
        encoded_pid = atoi(buffer);

        /* if pid < 0, the pid is for postgres, not postmaster */
        other_pid = (pid_t) (encoded_pid < 0 ? -encoded_pid : encoded_pid);

        if (other_pid <= 0)
            elog(FATAL, "bogus data in lock file \"%s\": \"%s\"",
                 filename, buffer);

        /*
         * Check to see if the other process still exists
         *
         * Per discussion above, my_pid, my_p_pid, and my_gp_pid can be
         * ignored as false matches.
         *
         * Normally kill() will fail with ESRCH if the given PID doesn't
         * exist.
         *
         * We can treat the EPERM-error case as okay because that error
         * implies that the existing process has a different userid than we
         * do, which means it cannot be a competing postmaster.  A postmaster
         * cannot successfully attach to a data directory owned by a userid
         * other than its own.  (This is now checked directly in
         * checkDataDir(), but has been true for a long time because of the
         * restriction that the data directory isn't group- or
         * world-accessible.)  Also, since we create the lockfiles mode 600,
         * we'd have failed above if the lockfile belonged to another userid
         * --- which means that whatever process kill() is reporting about
         * isn't the one that made the lockfile.  (NOTE: this last
         * consideration is the only one that keeps us from blowing away a
         * Unix socket file belonging to an instance of Postgres being run by
         * someone else, at least on machines where /tmp hasn't got a
         * stickybit.)
         */
        if (other_pid != my_pid && other_pid != my_p_pid &&
            other_pid != my_gp_pid)
        {
            if (kill(other_pid, 0) == 0 ||
                (errno != ESRCH && errno != EPERM))
            {
                /* lockfile belongs to a live process */
                ereport(FATAL,
                        (errcode(ERRCODE_LOCK_FILE_EXISTS),
                         errmsg("lock file \"%s\" already exists",
                                filename),
                         isDDLock ?
                         (encoded_pid < 0 ?
                          errhint("Is another postgres (PID %d) running in data directory \"%s\"?",
                                  (int) other_pid, refName) :
                          errhint("Is another postmaster (PID %d) running in data directory \"%s\"?",
                                  (int) other_pid, refName)) :
                         (encoded_pid < 0 ?
                          errhint("Is another postgres (PID %d) using socket file \"%s\"?",
                                  (int) other_pid, refName) :
                          errhint("Is another postmaster (PID %d) using socket file \"%s\"?",
                                  (int) other_pid, refName))));
            }
        }

        /*
         * No, the creating process did not exist.  However, it could be that
         * the postmaster crashed (or more likely was kill -9'd by a clueless
         * admin) but has left orphan backends behind.  Check for this by
         * looking to see if there is an associated shmem segment that is
         * still in use.
         *
         * Note: because postmaster.pid is written in multiple steps, we might
         * not find the shmem ID values in it; we can't treat that as an
         * error.
         */
        if (isDDLock)
        {
            char       *ptr = buffer;
            unsigned long id1,
                        id2;
            int         lineno;

            for (lineno = 1; lineno < LOCK_FILE_LINE_SHMEM_KEY; lineno++)
            {
                if ((ptr = strchr(ptr, '\n')) == NULL)
                    break;
                ptr++;
            }

            if (ptr != NULL &&
                sscanf(ptr, "%lu %lu", &id1, &id2) == 2)
            {
                if (PGSharedMemoryIsInUse(id1, id2))
                    ereport(FATAL,
                            (errcode(ERRCODE_LOCK_FILE_EXISTS),
                             errmsg("pre-existing shared memory block "
                                    "(key %lu, ID %lu) is still in use",
                                    id1, id2),
                             errhint("If you're sure there are no old "
                                     "server processes still running, remove "
                                     "the shared memory block "
                                     "or just delete the file \"%s\".",
                                     filename)));
            }
        }

        /*
         * Looks like nobody's home.  Unlink the file and try again to create
         * it.  Need a loop because of possible race condition against other
         * would-be creators.
         */
        if (unlink(filename) < 0)
            ereport(FATAL,
                    (errcode_for_file_access(),
                     errmsg("could not remove old lock file \"%s\": %m",
                            filename),
                     errhint("The file seems accidentally left over, but "
                             "it could not be removed. Please remove the file "
                             "by hand and try again.")));
    }

    /*
     * Successfully created the file, now fill it.  See comment in miscadmin.h
     * about the contents.  Note that we write the same first five lines into
     * both datadir and socket lockfiles; although more stuff may get added to
     * the datadir lockfile later.
     */
    snprintf(buffer, sizeof(buffer), "%d\n%s\n%ld\n%d\n%s\n",
             amPostmaster ? (int) my_pid : -((int) my_pid),
             DataDir,
             (long) MyStartTime,
             PostPortNumber,
             socketDir);

    /*
     * In a standalone backend, the next line (LOCK_FILE_LINE_LISTEN_ADDR)
     * will never receive data, so fill it in as empty now.
     */
    if (isDDLock && !amPostmaster)
        strlcat(buffer, "\n", sizeof(buffer));

    errno = 0;
    pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_CREATE_WRITE);
    if (write(fd, buffer, strlen(buffer)) != strlen(buffer))
    {
        int         save_errno = errno;

        close(fd);
        unlink(filename);
        /* if write didn't set errno, assume problem is no disk space */
        errno = save_errno ? save_errno : ENOSPC;
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg("could not write lock file \"%s\": %m", filename)));
    }
    pgstat_report_wait_end();

    pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_CREATE_SYNC);
    if (pg_fsync(fd) != 0)
    {
        int         save_errno = errno;

        close(fd);
        unlink(filename);
        errno = save_errno;
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg("could not write lock file \"%s\": %m", filename)));
    }
    pgstat_report_wait_end();
    if (close(fd) != 0)
    {
        int         save_errno = errno;

        unlink(filename);
        errno = save_errno;
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg("could not write lock file \"%s\": %m", filename)));
    }

    /*
     * Arrange to unlink the lock file(s) at proc_exit.  If this is the first
     * one, set up the on_proc_exit function to do it; then add this lock file
     * to the list of files to unlink.
     */
    if (lock_files == NIL)
        on_proc_exit(UnlinkLockFiles, 0);

    /*
     * Use lcons so that the lock files are unlinked in reverse order of
     * creation; this is critical!
     */
    lock_files = lcons(pstrdup(filename), lock_files);
}

/*
 * Create the data directory lockfile.
 *
 * When this is called, we must have already switched the working
 * directory to DataDir, so we can just use a relative path.  This
 * helps ensure that we are locking the directory we should be.
 *
 * Note that the socket directory path line is initially written as empty.
 * postmaster.c will rewrite it upon creating the first Unix socket.
 */
void
CreateDataDirLockFile(bool amPostmaster)
{
    CreateLockFile(DIRECTORY_LOCK_FILE, amPostmaster, "", true, DataDir);
}

/*
 * Create a lockfile for the specified Unix socket file.
 */
void
CreateSocketLockFile(const char *socketfile, bool amPostmaster,
                     const char *socketDir)
{
    char        lockfile[MAXPGPATH];

    snprintf(lockfile, sizeof(lockfile), "%s.lock", socketfile);
    CreateLockFile(lockfile, amPostmaster, socketDir, false, socketfile);
}

/*
 * TouchSocketLockFiles -- mark socket lock files as recently accessed
 *
 * This routine should be called every so often to ensure that the socket
 * lock files have a recent mod or access date.  That saves them
 * from being removed by overenthusiastic /tmp-directory-cleaner daemons.
 * (Another reason we should never have put the socket file in /tmp...)
 */
void
TouchSocketLockFiles(void)
{
    ListCell   *l;

    foreach(l, lock_files)
    {
        char       *socketLockFile = (char *) lfirst(l);

        /* No need to touch the data directory lock file, we trust */
        if (strcmp(socketLockFile, DIRECTORY_LOCK_FILE) == 0)
            continue;

        /*
         * utime() is POSIX standard, utimes() is a common alternative; if we
         * have neither, fall back to actually reading the file (which only
         * sets the access time not mod time, but that should be enough in
         * most cases).  In all paths, we ignore errors.
         */
#ifdef HAVE_UTIME
        utime(socketLockFile, NULL);
#else                           /* !HAVE_UTIME */
#ifdef HAVE_UTIMES
        utimes(socketLockFile, NULL);
#else                           /* !HAVE_UTIMES */
        int         fd;
        char        buffer[1];

        fd = open(socketLockFile, O_RDONLY | PG_BINARY, 0);
        if (fd >= 0)
        {
            read(fd, buffer, sizeof(buffer));
            close(fd);
        }
#endif                          /* HAVE_UTIMES */
#endif                          /* HAVE_UTIME */
    }
}


/*
 * Add (or replace) a line in the data directory lock file.
 * The given string should not include a trailing newline.
 *
 * Note: because we don't truncate the file, if we were to rewrite a line
 * with less data than it had before, there would be garbage after the last
 * line.  We don't ever actually do that, so not worth adding another kernel
 * call to cover the possibility.
 */
void
AddToDataDirLockFile(int target_line, const char *str)
{
    int         fd;
    int         len;
    int         lineno;
    char       *srcptr;
    char       *destptr;
    char        srcbuffer[BLCKSZ];
    char        destbuffer[BLCKSZ];

    fd = open(DIRECTORY_LOCK_FILE, O_RDWR | PG_BINARY, 0);
    if (fd < 0)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not open file \"%s\": %m",
                        DIRECTORY_LOCK_FILE)));
        return;
    }
    pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_ADDTODATADIR_READ);
    len = read(fd, srcbuffer, sizeof(srcbuffer) - 1);
    pgstat_report_wait_end();
    if (len < 0)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not read from file \"%s\": %m",
                        DIRECTORY_LOCK_FILE)));
        close(fd);
        return;
    }
    srcbuffer[len] = '\0';

    /*
     * Advance over lines we are not supposed to rewrite, then copy them to
     * destbuffer.
     */
    srcptr = srcbuffer;
    for (lineno = 1; lineno < target_line; lineno++)
    {
        if ((srcptr = strchr(srcptr, '\n')) == NULL)
        {
            elog(LOG, "incomplete data in \"%s\": found only %d newlines while trying to add line %d",
                 DIRECTORY_LOCK_FILE, lineno - 1, target_line);
            close(fd);
            return;
        }
        srcptr++;
    }
    memcpy(destbuffer, srcbuffer, srcptr - srcbuffer);
    destptr = destbuffer + (srcptr - srcbuffer);

    /*
     * Write or rewrite the target line.
     */
    snprintf(destptr, destbuffer + sizeof(destbuffer) - destptr, "%s\n", str);
    destptr += strlen(destptr);

    /*
     * If there are more lines in the old file, append them to destbuffer.
     */
    if ((srcptr = strchr(srcptr, '\n')) != NULL)
    {
        srcptr++;
        snprintf(destptr, destbuffer + sizeof(destbuffer) - destptr, "%s",
                 srcptr);
    }

    /*
     * And rewrite the data.  Since we write in a single kernel call, this
     * update should appear atomic to onlookers.
     */
    len = strlen(destbuffer);
    errno = 0;
    pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_ADDTODATADIR_WRITE);
    if (lseek(fd, (off_t) 0, SEEK_SET) != 0 ||
        (int) write(fd, destbuffer, len) != len)
    {
        pgstat_report_wait_end();
        /* if write didn't set errno, assume problem is no disk space */
        if (errno == 0)
            errno = ENOSPC;
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m",
                        DIRECTORY_LOCK_FILE)));
        close(fd);
        return;
    }
    pgstat_report_wait_end();
    pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_ADDTODATADIR_SYNC);
    if (pg_fsync(fd) != 0)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m",
                        DIRECTORY_LOCK_FILE)));
    }
    pgstat_report_wait_end();
    if (close(fd) != 0)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m",
                        DIRECTORY_LOCK_FILE)));
    }
}


/*
 * Recheck that the data directory lock file still exists with expected
 * content.  Return TRUE if the lock file appears OK, FALSE if it isn't.
 *
 * We call this periodically in the postmaster.  The idea is that if the
 * lock file has been removed or replaced by another postmaster, we should
 * do a panic database shutdown.  Therefore, we should return TRUE if there
 * is any doubt: we do not want to cause a panic shutdown unnecessarily.
 * Transient failures like EINTR or ENFILE should not cause us to fail.
 * (If there really is something wrong, we'll detect it on a future recheck.)
 */
bool
RecheckDataDirLockFile(void)
{
    int         fd;
    int         len;
    long        file_pid;
    char        buffer[BLCKSZ];

    fd = open(DIRECTORY_LOCK_FILE, O_RDWR | PG_BINARY, 0);
    if (fd < 0)
    {
        /*
         * There are many foreseeable false-positive error conditions.  For
         * safety, fail only on enumerated clearly-something-is-wrong
         * conditions.
         */
        switch (errno)
        {
            case ENOENT:
            case ENOTDIR:
                /* disaster */
                ereport(LOG,
                        (errcode_for_file_access(),
                         errmsg("could not open file \"%s\": %m",
                                DIRECTORY_LOCK_FILE)));
                return false;
            default:
                /* non-fatal, at least for now */
                ereport(LOG,
                        (errcode_for_file_access(),
                         errmsg("could not open file \"%s\": %m; continuing anyway",
                                DIRECTORY_LOCK_FILE)));
                return true;
        }
    }
    pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_RECHECKDATADIR_READ);
    len = read(fd, buffer, sizeof(buffer) - 1);
    pgstat_report_wait_end();
    if (len < 0)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not read from file \"%s\": %m",
                        DIRECTORY_LOCK_FILE)));
        close(fd);
        return true;            /* treat read failure as nonfatal */
    }
    buffer[len] = '\0';
    close(fd);
    file_pid = atol(buffer);
    if (file_pid == getpid())
        return true;            /* all is well */

    /* Trouble: someone's overwritten the lock file */
    ereport(LOG,
            (errmsg("lock file \"%s\" contains wrong PID: %ld instead of %ld",
                    DIRECTORY_LOCK_FILE, file_pid, (long) getpid())));
    return false;
}


/*-------------------------------------------------------------------------
 *              Version checking support
 *-------------------------------------------------------------------------
 */

/*
 * Determine whether the PG_VERSION file in directory `path' indicates
 * a data version compatible with the version of this program.
 *
 * If compatible, return. Otherwise, ereport(FATAL).
 */
void
ValidatePgVersion(const char *path)
{
    char        full_path[MAXPGPATH];
    FILE       *file;
    int         ret;
    long        file_major;
    long        my_major;
    char       *endptr;
    char        file_version_string[64];
    const char *my_version_string = PG_VERSION;

    my_major = strtol(my_version_string, &endptr, 10);

    snprintf(full_path, sizeof(full_path), "%s/PG_VERSION", path);

    file = AllocateFile(full_path, "r");
    if (!file)
    {
        if (errno == ENOENT)
            ereport(FATAL,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("\"%s\" is not a valid data directory",
                            path),
                     errdetail("File \"%s\" is missing.", full_path)));
        else
            ereport(FATAL,
                    (errcode_for_file_access(),
                     errmsg("could not open file \"%s\": %m", full_path)));
    }

    file_version_string[0] = '\0';
    ret = fscanf(file, "%63s", file_version_string);
    file_major = strtol(file_version_string, &endptr, 10);

    if (ret != 1 || endptr == file_version_string)
        ereport(FATAL,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("\"%s\" is not a valid data directory",
                        path),
                 errdetail("File \"%s\" does not contain valid data.",
                           full_path),
                 errhint("You might need to initdb.")));

    FreeFile(file);

    if (my_major != file_major)
        ereport(FATAL,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("database files are incompatible with server"),
                 errdetail("The data directory was initialized by PostgreSQL version %s, "
                           "which is not compatible with this version %s.",
                           file_version_string, my_version_string)));
}

/*-------------------------------------------------------------------------
 *              Library preload support
 *-------------------------------------------------------------------------
 */

/*
 * GUC variables: lists of library names to be preloaded at postmaster
 * start and at backend start
 */
char       *session_preload_libraries_string = NULL;
char       *shared_preload_libraries_string = NULL;
char       *local_preload_libraries_string = NULL;

/* Flag telling that we are loading shared_preload_libraries */
bool        process_shared_preload_libraries_in_progress = false;

/*
 * load the shared libraries listed in 'libraries'
 *
 * 'gucname': name of GUC variable, for error reports
 * 'restricted': if true, force libraries to be in $libdir/plugins/
 */
static void
load_libraries(const char *libraries, const char *gucname, bool restricted)
{
    char       *rawstring;
    List       *elemlist;
    ListCell   *l;

    if (libraries == NULL || libraries[0] == '\0')
        return;                 /* nothing to do */

    /* Need a modifiable copy of string */
    rawstring = pstrdup(libraries);

    /* Parse string into list of filename paths */
    if (!SplitDirectoriesString(rawstring, ',', &elemlist))
    {
        /* syntax error in list */
        list_free_deep(elemlist);
        pfree(rawstring);
        ereport(LOG,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("invalid list syntax in parameter \"%s\"",
                        gucname)));
        return;
    }

    foreach(l, elemlist)
    {
        /* Note that filename was already canonicalized */
        char       *filename = (char *) lfirst(l);
        char       *expanded = NULL;

        /* If restricting, insert $libdir/plugins if not mentioned already */
        if (restricted && first_dir_separator(filename) == NULL)
        {
            expanded = psprintf("$libdir/plugins/%s", filename);
            filename = expanded;
        }
        load_file(filename, restricted);
        ereport(DEBUG1,
                (errmsg("loaded library \"%s\"", filename)));
        if (expanded)
            pfree(expanded);
    }

    list_free_deep(elemlist);
    pfree(rawstring);
}

/*
 * process any libraries that should be preloaded at postmaster start
 */
void
process_shared_preload_libraries(void)
{
    process_shared_preload_libraries_in_progress = true;
    load_libraries(shared_preload_libraries_string,
                   "shared_preload_libraries",
                   false);
    process_shared_preload_libraries_in_progress = false;
}

/*
 * process any libraries that should be preloaded at backend start
 */
void
process_session_preload_libraries(void)
{
    load_libraries(session_preload_libraries_string,
                   "session_preload_libraries",
                   false);
    load_libraries(local_preload_libraries_string,
                   "local_preload_libraries",
                   true);
}

void
pg_bindtextdomain(const char *domain)
{
#ifdef ENABLE_NLS
    if (my_exec_path[0] != '\0')
    {
        char        locale_path[MAXPGPATH];

        get_locale_path(my_exec_path, locale_path);
        bindtextdomain(domain, locale_path);
        pg_bind_textdomain_codeset(domain);
    }
#endif
}