miscinit.c

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/*-------------------------------------------------------------------------
 *
 * miscinit.c
 *    miscellaneous initialization support stuff
 *
 * Portions Copyright (c) 1996-2026, 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>
#include <utime.h>
 
#include "access/htup_details.h"
#include "access/parallel.h"
#include "catalog/pg_authid.h"
#include "common/file_perm.h"
#include "libpq/libpq.h"
#include "libpq/pqsignal.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#include "postmaster/interrupt.h"
#include "postmaster/postmaster.h"
#include "replication/slotsync.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/pg_shmem.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/pidfile.h"
#include "utils/syscache.h"
#include "utils/varlena.h"
#include "utils/wait_event.h"
 
 
#define DIRECTORY_LOCK_FILE     "postmaster.pid"
 
ProcessingMode Mode = InitProcessing;
 
BackendType MyBackendType;
 
/* 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;
 
 
/* ----------------------------------------------------------------
 *  common process startup code
 * ----------------------------------------------------------------
 */
 
/*
 * Initialize the basic environment for a postmaster child
 *
 * Should be called as early as possible after the child's startup. However,
 * on EXEC_BACKEND builds it does need to be after read_backend_variables().
 */
void
InitPostmasterChild(void)
{
    IsUnderPostmaster = true;   /* we are a postmaster subprocess now */
 
    /*
     * Start our win32 signal implementation. This has to be done after we
     * read the backend variables, because we need to pick up the signal pipe
     * from the parent process.
     */
#ifdef WIN32
    pgwin32_signal_initialize();
#endif
 
    InitProcessGlobals();
 
    /*
     * 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();
 
    /* In EXEC_BACKEND case we will not have inherited BlockSig etc values */
#ifdef EXEC_BACKEND
    pqinitmask();
#endif
 
    /* Initialize process-local latch support */
    InitializeWaitEventSupport();
    InitProcessLocalLatch();
    InitializeLatchWaitSet();
 
    /*
     * 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
 
    /*
     * Every postmaster child process is expected to respond promptly to
     * SIGQUIT at all times.  Therefore we centrally remove SIGQUIT from
     * BlockSig and install a suitable signal handler.  (Client-facing
     * processes may choose to replace this default choice of handler with
     * quickdie().)  All other blockable signals remain blocked for now.
     */
    pqsignal(SIGQUIT, SignalHandlerForCrashExit);
 
    sigdelset(&BlockSig, SIGQUIT);
    sigprocmask(SIG_SETMASK, &BlockSig, NULL);
 
    /* Request a signal if the postmaster dies, if possible. */
    PostmasterDeathSignalInit();
 
    /* Don't give the pipe to subprograms that we execute. */
#ifndef WIN32
    if (fcntl(postmaster_alive_fds[POSTMASTER_FD_WATCH], F_SETFD, FD_CLOEXEC) < 0)
        ereport(FATAL,
                (errcode_for_socket_access(),
                 errmsg_internal("could not set postmaster death monitoring pipe to FD_CLOEXEC mode: %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);
 
    MyBackendType = B_STANDALONE_BACKEND;
 
    /*
     * Start our win32 signal implementation
     */
#ifdef WIN32
    pgwin32_signal_initialize();
#endif
 
    InitProcessGlobals();
 
    /* Initialize process-local latch support */
    InitializeWaitEventSupport();
    InitProcessLocalLatch();
    InitializeLatchWaitSet();
 
    /*
     * For consistency with InitPostmasterChild, initialize signal mask here.
     * But we don't unblock SIGQUIT or provide a default handler for it.
     */
    pqinitmask();
    sigprocmask(SIG_SETMASK, &BlockSig, NULL);
 
    /* 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, FeBeWaitSetLatchPos, 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
InitProcessLocalLatch(void)
{
    MyLatch = &LocalLatchData;
    InitLatch(MyLatch);
}
 
void
SwitchBackToLocalLatch(void)
{
    Assert(MyLatch != &LocalLatchData);
    Assert(MyProc != NULL && MyLatch == &MyProc->procLatch);
 
    MyLatch = &LocalLatchData;
 
    if (FeBeWaitSet)
        ModifyWaitEvent(FeBeWaitSet, FeBeWaitSetLatchPos, WL_LATCH_SET,
                        MyLatch);
 
    SetLatch(MyLatch);
}
 
/*
 * Return a human-readable string representation of a BackendType.
 *
 * The string is not localized here, but we mark the strings for translation
 * so that callers can invoke _() on the result.
 */
const char *
GetBackendTypeDesc(BackendType backendType)
{
    const char *backendDesc = gettext_noop("unknown process type");
 
    switch (backendType)
    {
#define PG_PROCTYPE(bktype, bkcategory, description, main_func, shmem_attach)   \
        case bktype: backendDesc = description; break;
#include "postmaster/proctypelist.h"
#undef PG_PROCTYPE
    }
    return backendDesc;
}
 
/* ----------------------------------------------------------------
 *              database path / name support stuff
 * ----------------------------------------------------------------
 */
 
void
SetDatabasePath(const char *path)
{
    /* This should happen only once per process */
    Assert(!DatabasePath);
    DatabasePath = MemoryContextStrdup(TopMemoryContext, path);
}
 
/*
 * Validate the proposed data directory.
 *
 * Also initialize file and directory create modes and mode mask.
 */
void
checkDataDir(void)
{
    struct stat stat_buf;
 
    Assert(DataDir);
 
    if (stat(DataDir, &stat_buf) != 0)
    {
        if (errno == ENOENT)
            ereport(FATAL,
                    (errcode_for_file_access(),
                     errmsg("data directory \"%s\" does not exist",
                            DataDir)));
        else
            ereport(FATAL,
                    (errcode_for_file_access(),
                     errmsg("could not read permissions of directory \"%s\": %m",
                            DataDir)));
    }
 
    /* eventual chdir would fail anyway, but let's test ... */
    if (!S_ISDIR(stat_buf.st_mode))
        ereport(FATAL,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("specified data directory \"%s\" is not a directory",
                        DataDir)));
 
    /*
     * Check that the directory belongs to my userid; if not, reject.
     *
     * This check is an essential part of the interlock that prevents two
     * postmasters from starting in the same directory (see CreateLockFile()).
     * Do not remove or weaken it.
     *
     * XXX can we safely enable this check on Windows?
     */
#if !defined(WIN32) && !defined(__CYGWIN__)
    if (stat_buf.st_uid != geteuid())
        ereport(FATAL,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("data directory \"%s\" has wrong ownership",
                        DataDir),
                 errhint("The server must be started by the user that owns the data directory.")));
#endif
 
    /*
     * Check if the directory has correct permissions.  If not, reject.
     *
     * Only two possible modes are allowed, 0700 and 0750.  The latter mode
     * indicates that group read/execute should be allowed on all newly
     * created files and directories.
     *
     * XXX temporarily suppress check when on Windows, because there may not
     * be proper support for Unix-y file permissions.  Need to think of a
     * reasonable check to apply on Windows.
     */
#if !defined(WIN32) && !defined(__CYGWIN__)
    if (stat_buf.st_mode & PG_MODE_MASK_GROUP)
        ereport(FATAL,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("data directory \"%s\" has invalid permissions",
                        DataDir),
                 errdetail("Permissions should be u=rwx (0700) or u=rwx,g=rx (0750).")));
#endif
 
    /*
     * Reset creation modes and mask based on the mode of the data directory.
     *
     * The mask was set earlier in startup to disallow group permissions on
     * newly created files and directories.  However, if group read/execute
     * are present on the data directory then modify the create modes and mask
     * to allow group read/execute on newly created files and directories and
     * set the data_directory_mode GUC.
     *
     * Suppress when on Windows, because there may not be proper support for
     * Unix-y file permissions.
     */
#if !defined(WIN32) && !defined(__CYGWIN__)
    SetDataDirectoryCreatePerm(stat_buf.st_mode);
 
    umask(pg_mode_mask);
    data_directory_mode = pg_dir_create_mode;
#endif
 
    /* Check for PG_VERSION */
    ValidatePgVersion(DataDir);
}
 
/*
 * Set data directory, but make sure it's an absolute path.  Use this,
 * never set DataDir directly.
 */
void
SetDataDir(const char *dir)
{
    char       *new;
 
    Assert(dir);
 
    /* If presented path is relative, convert to absolute */
    new = make_absolute_path(dir);
 
    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)
{
    Assert(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 AuthenticatedUserId is a
 * superuser).  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;
static const char *SystemUser = NULL;
 
/* We also have to remember the superuser state of the session user */
static bool SessionUserIsSuperuser = false;
 
static int  SecurityRestrictionContext = 0;
 
/* We also remember if a SET ROLE is currently active */
static bool SetRoleIsActive = false;
 
/*
 * GetUserId - get the current effective user ID.
 *
 * Note: there's no SetUserId() anymore; use SetUserIdAndSecContext().
 */
Oid
GetUserId(void)
{
    Assert(OidIsValid(CurrentUserId));
    return CurrentUserId;
}
 
 
/*
 * GetOuterUserId/SetOuterUserId - get/set the outer-level user ID.
 */
Oid
GetOuterUserId(void)
{
    Assert(OidIsValid(OuterUserId));
    return OuterUserId;
}
 
 
static void
SetOuterUserId(Oid userid, bool is_superuser)
{
    Assert(SecurityRestrictionContext == 0);
    Assert(OidIsValid(userid));
    OuterUserId = userid;
 
    /* We force the effective user ID to match, too */
    CurrentUserId = userid;
 
    /* Also update the is_superuser GUC to match OuterUserId's property */
    SetConfigOption("is_superuser",
                    is_superuser ? "on" : "off",
                    PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
}
 
 
/*
 * GetSessionUserId/SetSessionUserId - get/set the session user ID.
 */
Oid
GetSessionUserId(void)
{
    Assert(OidIsValid(SessionUserId));
    return SessionUserId;
}
 
bool
GetSessionUserIsSuperuser(void)
{
    Assert(OidIsValid(SessionUserId));
    return SessionUserIsSuperuser;
}
 
static void
SetSessionUserId(Oid userid, bool is_superuser)
{
    Assert(SecurityRestrictionContext == 0);
    Assert(OidIsValid(userid));
    SessionUserId = userid;
    SessionUserIsSuperuser = is_superuser;
}
 
/*
 * Return the system user representing the authenticated identity.
 * It is defined in InitializeSystemUser() as auth_method:authn_id.
 */
const char *
GetSystemUser(void)
{
    return SystemUser;
}
 
/*
 * GetAuthenticatedUserId/SetAuthenticatedUserId - get/set the authenticated
 * user ID
 */
Oid
GetAuthenticatedUserId(void)
{
    Assert(OidIsValid(AuthenticatedUserId));
    return AuthenticatedUserId;
}
 
void
SetAuthenticatedUserId(Oid userid)
{
    Assert(OidIsValid(userid));
 
    /* call only once */
    Assert(!OidIsValid(AuthenticatedUserId));
 
    AuthenticatedUserId = userid;
 
    /* Also mark our PGPROC entry with the authenticated user id */
    /* (We assume this is an atomic store so no lock is needed) */
    MyProc->roleId = userid;
}
 
 
/*
 * 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.  The
 * policy is to use this before operations, e.g. autovacuum and REINDEX, that
 * enumerate relations of a database or schema and run functions associated
 * with each found relation.  The relation owner is the new user ID.  Set this
 * as soon as possible after locking the relation.  Restore the old user ID as
 * late as possible before closing the relation; restoring it shortly after
 * close is also tolerable.  If a command has both relation-enumerating and
 * non-enumerating modes, e.g. ANALYZE, both modes set this bit.  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.  These restrictions are fairly
 * draconian, but the functions called in relation-enumerating operations are
 * really supposed to be side-effect-free anyway.
 *
 * 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;
 
    /* Superusers bypass all permission checking. */
    if (superuser_arg(roleid))
        return true;
 
    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,
                        bool bypass_login_check)
{
    HeapTuple   roleTup;
    Form_pg_authid rform;
    char       *rname;
    bool        is_superuser;
 
    /*
     * In a parallel worker, we don't have to do anything here.
     * ParallelWorkerMain already set our output variables, and we aren't
     * going to enforce either rolcanlogin or rolconnlimit.  Furthermore, we
     * don't really want to perform a catalog lookup for the role: we don't
     * want to fail if it's been dropped.
     */
    if (InitializingParallelWorker)
    {
        Assert(bypass_login_check);
        return;
    }
 
    /*
     * Don't do scans if we're bootstrapping, none of the system catalogs
     * exist yet, and they should be owned by postgres anyway.
     */
    Assert(!IsBootstrapProcessingMode());
 
    /*
     * Make sure syscache entries are flushed for recent catalog changes. This
     * allows us to find roles that were created on-the-fly during
     * authentication.
     */
    AcceptInvalidationMessages();
 
    /*
     * Look up the role, either by name if that's given or by OID if not.
     */
    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 = rform->oid;
    rname = NameStr(rform->rolname);
    is_superuser = rform->rolsuper;
 
    SetAuthenticatedUserId(roleid);
 
    /*
     * Set SessionUserId and related variables, including "role", via the GUC
     * mechanisms.
     *
     * Note: ideally we would use PGC_S_DYNAMIC_DEFAULT here, so that
     * session_authorization could subsequently be changed from
     * pg_db_role_setting entries.  Instead, session_authorization in
     * pg_db_role_setting has no effect.  Changing that would require solving
     * two problems:
     *
     * 1. If pg_db_role_setting has values for both session_authorization and
     * role, we could not be sure which order those would be applied in, and
     * it would matter.
     *
     * 2. Sites may have years-old session_authorization entries.  There's not
     * been any particular reason to remove them.  Ending the dormancy of
     * those entries could seriously change application behavior, so only a
     * major release should do that.
     */
    SetConfigOption("session_authorization", rname,
                    PGC_BACKEND, PGC_S_OVERRIDE);
 
    /*
     * 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?  (But background workers can
         * override this by setting bypass_login_check.)
         */
        if (!bypass_login_check && !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.  We enforce the limit only
         * for regular backends, since other process types have their own
         * PGPROC pools.
         *
         * 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 &&
            AmRegularBackendProcess() &&
            !is_superuser &&
            CountUserBackends(roleid) > rform->rolconnlimit)
            ereport(FATAL,
                    (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                     errmsg("too many connections for role \"%s\"",
                            rname)));
    }
 
    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, in slot sync worker and in background workers.
     */
    Assert(!IsUnderPostmaster || AmAutoVacuumWorkerProcess() ||
           AmLogicalSlotSyncWorkerProcess() || AmBackgroundWorkerProcess());
 
    /* call only once */
    Assert(!OidIsValid(AuthenticatedUserId));
 
    AuthenticatedUserId = BOOTSTRAP_SUPERUSERID;
 
    /*
     * XXX Ideally we'd do this via SetConfigOption("session_authorization"),
     * but we lack the role name needed to do that, and we can't fetch it
     * because one reason for this special case is to be able to start up even
     * if something's happened to the BOOTSTRAP_SUPERUSERID's pg_authid row.
     * Since we don't set the GUC itself, C code will see the value as NULL,
     * and current_setting() will report an empty string within this session.
     */
    SetSessionAuthorization(BOOTSTRAP_SUPERUSERID, true);
 
    /* We could do SetConfigOption("role"), but let's be consistent */
    SetCurrentRoleId(InvalidOid, false);
}
 
/*
 * Initialize the system user.
 *
 * This is built as auth_method:authn_id.
 */
void
InitializeSystemUser(const char *authn_id, const char *auth_method)
{
    char       *system_user;
 
    /* call only once */
    Assert(SystemUser == NULL);
 
    /*
     * InitializeSystemUser should be called only when authn_id is not NULL,
     * meaning that auth_method is valid.
     */
    Assert(authn_id != NULL);
 
    system_user = psprintf("%s:%s", auth_method, authn_id);
 
    /* Store SystemUser in long-lived storage */
    SystemUser = MemoryContextStrdup(TopMemoryContext, system_user);
    pfree(system_user);
}
 
/*
 * SQL-function SYSTEM_USER
 */
Datum
system_user(PG_FUNCTION_ARGS)
{
    const char *sysuser = GetSystemUser();
 
    if (sysuser)
        PG_RETURN_DATUM(CStringGetTextDatum(sysuser));
    else
        PG_RETURN_NULL();
}
 
/*
 * Change session auth ID while running
 *
 * The SQL standard says that SET SESSION AUTHORIZATION implies SET ROLE NONE.
 * We mechanize that at higher levels not here, because this is the GUC
 * assign hook for "session_authorization", and it must be commutative with
 * SetCurrentRoleId (the hook for "role") because guc.c provides no guarantees
 * which will run first during cases such as transaction rollback.  Therefore,
 * we update derived state (OuterUserId/CurrentUserId/is_superuser) only if
 * !SetRoleIsActive.
 */
void
SetSessionAuthorization(Oid userid, bool is_superuser)
{
    SetSessionUserId(userid, is_superuser);
 
    if (!SetRoleIsActive)
        SetOuterUserId(userid, is_superuser);
}
 
/*
 * 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, do nothing beyond updating
     * SetRoleIsActive --- the eventual SetSessionAuthorization call will
     * update the derived state.  This is needed since we will get called
     * during GUC initialization.
     */
    if (!OidIsValid(roleid))
    {
        SetRoleIsActive = false;
 
        if (!OidIsValid(SessionUserId))
            return;
 
        roleid = SessionUserId;
        is_superuser = SessionUserIsSuperuser;
    }
    else
        SetRoleIsActive = true;
 
    SetOuterUserId(roleid, is_superuser);
}
 
 
/*
 * 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;
}
 
/* ------------------------------------------------------------------------
 *              Client connection state shared with parallel workers
 *
 * ClientConnectionInfo contains pieces of information about the client that
 * need to be synced to parallel workers when they initialize.
 *-------------------------------------------------------------------------
 */
 
ClientConnectionInfo MyClientConnectionInfo;
 
/*
 * Intermediate representation of ClientConnectionInfo for easier
 * serialization.  Variable-length fields are allocated right after this
 * header.
 */
typedef struct SerializedClientConnectionInfo
{
    int32       authn_id_len;   /* strlen(authn_id), or -1 if NULL */
    UserAuth    auth_method;
} SerializedClientConnectionInfo;
 
/*
 * Calculate the space needed to serialize MyClientConnectionInfo.
 */
Size
EstimateClientConnectionInfoSpace(void)
{
    Size        size = 0;
 
    size = add_size(size, sizeof(SerializedClientConnectionInfo));
 
    if (MyClientConnectionInfo.authn_id)
        size = add_size(size, strlen(MyClientConnectionInfo.authn_id) + 1);
 
    return size;
}
 
/*
 * Serialize MyClientConnectionInfo for use by parallel workers.
 */
void
SerializeClientConnectionInfo(Size maxsize PG_USED_FOR_ASSERTS_ONLY,
                              char *start_address)
{
    SerializedClientConnectionInfo serialized = {0};
 
    serialized.authn_id_len = -1;
    serialized.auth_method = MyClientConnectionInfo.auth_method;
 
    if (MyClientConnectionInfo.authn_id)
        serialized.authn_id_len = strlen(MyClientConnectionInfo.authn_id);
 
    /* Copy serialized representation to buffer */
    Assert(maxsize >= sizeof(serialized));
    memcpy(start_address, &serialized, sizeof(serialized));
 
    maxsize -= sizeof(serialized);
    start_address += sizeof(serialized);
 
    /* Copy authn_id into the space after the struct */
    if (serialized.authn_id_len >= 0)
    {
        Assert(maxsize >= (serialized.authn_id_len + 1));
        memcpy(start_address,
               MyClientConnectionInfo.authn_id,
        /* include the NULL terminator to ease deserialization */
               serialized.authn_id_len + 1);
    }
}
 
/*
 * Restore MyClientConnectionInfo from its serialized representation.
 */
void
RestoreClientConnectionInfo(char *conninfo)
{
    SerializedClientConnectionInfo serialized;
 
    memcpy(&serialized, conninfo, sizeof(serialized));
 
    /* Copy the fields back into place */
    MyClientConnectionInfo.authn_id = NULL;
    MyClientConnectionInfo.auth_method = serialized.auth_method;
 
    if (serialized.authn_id_len >= 0)
    {
        char       *authn_id;
 
        authn_id = conninfo + sizeof(serialized);
        MyClientConnectionInfo.authn_id = MemoryContextStrdup(TopMemoryContext,
                                                              authn_id);
    }
}
 
 
/*-------------------------------------------------------------------------
 *              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 pidfile.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 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 0600/0640.  See
         * comments below.
         */
        fd = open(filename, O_RDWR | O_CREAT | O_EXCL, pg_file_create_mode);
        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, pg_file_create_mode);
        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, as enforced in checkDataDir(). Also, since we
         * create the lockfiles mode 0600/0640, 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("Terminate any old server processes associated with data directory \"%s\".",
                                     refName)));
            }
        }
 
        /*
         * 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 pidfile.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" INT64_FORMAT "\n%d\n%s\n",
             amPostmaster ? (int) my_pid : -((int) my_pid),
             DataDir,
             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;
 
        /* we just ignore any error here */
        (void) utime(socketLockFile, NULL);
    }
}
 
 
/*
 * 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.  While we could fix that by adding a truncate call, that would make
 * the file update non-atomic, which we'd rather avoid.  Therefore, callers
 * should endeavor never to shorten a line once it's been written.
 */
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++)
    {
        char       *eol = strchr(srcptr, '\n');
 
        if (eol == NULL)
            break;              /* not enough lines in file yet */
        srcptr = eol + 1;
    }
    memcpy(destbuffer, srcbuffer, srcptr - srcbuffer);
    destptr = destbuffer + (srcptr - srcbuffer);
 
    /*
     * Fill in any missing lines before the target line, in case lines are
     * added to the file out of order.
     */
    for (; lineno < target_line; lineno++)
    {
        if (destptr < destbuffer + sizeof(destbuffer))
            *destptr++ = '\n';
    }
 
    /*
     * 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 (pg_pwrite(fd, destbuffer, len, 0) != 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;
bool        process_shared_preload_libraries_done = false;
 
shmem_request_hook_type shmem_request_hook = NULL;
bool        process_shmem_requests_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_internal("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_shared_preload_libraries_done = true;
}
 
/*
 * 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);
}
 
/*
 * process any shared memory requests from preloaded libraries
 */
void
process_shmem_requests(void)
{
    process_shmem_requests_in_progress = true;
    if (shmem_request_hook)
        shmem_request_hook();
    process_shmem_requests_in_progress = false;
}
 
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
}