Revert dubious message wording change.

[PostgreSQL.git] / src / backend / utils / init / miscinit.c

/*-------------------------------------------------------------------------
 *
 * miscinit.c
 *        miscellaneous initialization support stuff
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <sys/param.h>
#include <signal.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 "catalog/pg_authid.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "postmaster/autovacuum.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/syscache.h"


#define DIRECTORY_LOCK_FILE             "postmaster.pid"

ProcessingMode Mode = InitProcessing;

/* Note: we rely on this to initialize as zeroes */
static char socketLockFile[MAXPGPATH];


/* ----------------------------------------------------------------
 *              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;

/* ----------------------------------------------------------------
 *              system index reindexing support
 *
 * When we are busy reindexing a system index, this code provides support
 * for preventing catalog lookups from using that index.
 * ----------------------------------------------------------------
 */

static Oid      currentlyReindexedHeap = InvalidOid;
static Oid      currentlyReindexedIndex = InvalidOid;

/*
 * ReindexIsProcessingHeap
 *              True if heap specified by OID is currently being reindexed.
 */
bool
ReindexIsProcessingHeap(Oid heapOid)
{
        return heapOid == currentlyReindexedHeap;
}

/*
 * ReindexIsProcessingIndex
 *              True if index specified by OID is currently being reindexed.
 */
bool
ReindexIsProcessingIndex(Oid indexOid)
{
        return indexOid == currentlyReindexedIndex;
}

/*
 * SetReindexProcessing
 *              Set flag that specified heap/index are being reindexed.
 */
void
SetReindexProcessing(Oid heapOid, Oid indexOid)
{
        Assert(OidIsValid(heapOid) && OidIsValid(indexOid));
        /* Reindexing is not re-entrant. */
        if (OidIsValid(currentlyReindexedIndex))
                elog(ERROR, "cannot reindex while reindexing");
        currentlyReindexedHeap = heapOid;
        currentlyReindexedIndex = indexOid;
}

/*
 * ResetReindexProcessing
 *              Unset reindexing status.
 */
void
ResetReindexProcessing(void)
{
        currentlyReindexedHeap = InvalidOid;
        currentlyReindexedIndex = InvalidOid;
}

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

void
SetDatabasePath(const char *path)
{
        if (DatabasePath)
        {
                free(DatabasePath);
                DatabasePath = NULL;
        }
        /* use strdup since this is done before memory contexts are set up */
        if (path)
        {
                DatabasePath = strdup(path);
                AssertState(DatabasePath);
        }
}

/*
 * 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)));
}

/*
 * If the given pathname isn't already absolute, make it so, interpreting
 * it relative to the current working directory.
 *
 * Also canonicalizes the path.  The result is always a malloc'd copy.
 *
 * Note: interpretation of relative-path arguments during postmaster startup
 * should happen before doing ChangeToDataDir(), else the user will probably
 * not like the results.
 */
char *
make_absolute_path(const char *path)
{
        char       *new;

        /* Returning null for null input is convenient for some callers */
        if (path == NULL)
                return NULL;

        if (!is_absolute_path(path))
        {
                char       *buf;
                size_t          buflen;

                buflen = MAXPGPATH;
                for (;;)
                {
                        buf = malloc(buflen);
                        if (!buf)
                                ereport(FATAL,
                                                (errcode(ERRCODE_OUT_OF_MEMORY),
                                                 errmsg("out of memory")));

                        if (getcwd(buf, buflen))
                                break;
                        else if (errno == ERANGE)
                        {
                                free(buf);
                                buflen *= 2;
                                continue;
                        }
                        else
                        {
                                free(buf);
                                elog(FATAL, "could not get current working directory: %m");
                        }
                }

                new = malloc(strlen(buf) + strlen(path) + 2);
                if (!new)
                        ereport(FATAL,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory")));
                sprintf(new, "%s/%s", buf, path);
                free(buf);
        }
        else
        {
                new = strdup(path);
                if (!new)
                        ereport(FATAL,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory")));
        }

        /* Make sure punctuation is canonical, too */
        canonicalize_path(new);

        return new;
}


/* ----------------------------------------------------------------
 *      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.
 *
 * SecurityDefinerContext is TRUE if we are within a SECURITY DEFINER function
 * or another context that temporarily changes CurrentUserId.
 * ----------------------------------------------------------------
 */
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 bool SecurityDefinerContext = false;

/* 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 SetUserIdAndContext().
 */
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(!SecurityDefinerContext);
        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(!SecurityDefinerContext);
        AssertArg(OidIsValid(userid));
        SessionUserId = userid;
        SessionUserIsSuperuser = is_superuser;
        SetRoleIsActive = false;

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


/*
 * GetUserIdAndContext/SetUserIdAndContext - get/set the current user ID
 * and the SecurityDefinerContext flag.
 *
 * Unlike GetUserId, GetUserIdAndContext does *not* Assert that the current
 * value of CurrentUserId is valid; nor does SetUserIdAndContext 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
GetUserIdAndContext(Oid *userid, bool *sec_def_context)
{
        *userid = CurrentUserId;
        *sec_def_context = SecurityDefinerContext;
}

void
SetUserIdAndContext(Oid userid, bool sec_def_context)
{
        CurrentUserId = userid;
        SecurityDefinerContext = sec_def_context;
}


/*
 * InSecurityDefinerContext - are we inside a SECURITY DEFINER context?
 */
bool
InSecurityDefinerContext(void)
{
        return SecurityDefinerContext;
}


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

        /*
         * 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));

        roleTup = SearchSysCache(AUTHNAME,
                                                         PointerGetDatum(rolename),
                                                         0, 0, 0);
        if (!HeapTupleIsValid(roleTup))
                ereport(FATAL,
                                (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                                 errmsg("role \"%s\" does not exist", rolename)));

        rform = (Form_pg_authid) GETSTRUCT(roleTup);
        roleid = HeapTupleGetOid(roleTup);

        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;".
         *
         * We do not enforce them for the autovacuum process either.
         */
        if (IsUnderPostmaster && !IsAutoVacuumWorkerProcess())
        {
                /*
                 * 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",
                                                        rolename)));

                /*
                 * 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\"",
                                                        rolename)));
        }

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

        /*
         * Set up user-specific configuration variables.  This is a good place to
         * do it so we don't have to read pg_authid twice during session startup.
         */
        datum = SysCacheGetAttr(AUTHNAME, roleTup,
                                                        Anum_pg_authid_rolconfig, &isnull);
        if (!isnull)
        {
                ArrayType  *a = DatumGetArrayTypeP(datum);

                /*
                 * We process all the options at SUSET level.  We assume that the
                 * right to insert an option into pg_authid was checked when it was
                 * inserted.
                 */
                ProcessGUCArray(a, PGC_SUSET, PGC_S_USER, GUC_ACTION_SET);
        }

        ReleaseSysCache(roleTup);
}


/*
 * Initialize user identity during special backend startup
 */
void
InitializeSessionUserIdStandalone(void)
{
        /* This function should only be called in a single-user backend. */
        AssertState(!IsUnderPostmaster || IsAutoVacuumWorkerProcess());

        /* 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
 */
char *
GetUserNameFromId(Oid roleid)
{
        HeapTuple       tuple;
        char       *result;

        tuple = SearchSysCache(AUTHOID,
                                                   ObjectIdGetDatum(roleid),
                                                   0, 0, 0);
        if (!HeapTupleIsValid(tuple))
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("invalid role OID: %u", roleid)));

        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
 * ($DATADIR/postmaster.pid) and a Unix-socket-file lockfile ($SOCKFILE.lock).
 * Both kinds of files contain the same info:
 *
 *              Owning process' PID
 *              Data directory path
 *
 * By convention, the owning process' PID is negated if it is a standalone
 * backend rather than a postmaster.  This is just for informational purposes.
 * The path is also just for informational purposes (so that a socket lockfile
 * can be more easily traced to the associated postmaster).
 *
 * A data-directory lockfile can optionally contain a third line, containing
 * the key and ID for the shared memory block used by this postmaster.
 *
 * On successful lockfile creation, a proc_exit callback to remove the
 * lockfile is automatically created.
 *-------------------------------------------------------------------------
 */

/*
 * proc_exit callback to remove a lockfile.
 */
static void
UnlinkLockFile(int status, Datum filename)
{
        char       *fname = (char *) DatumGetPointer(filename);

        if (fname != NULL)
        {
                if (unlink(fname) != 0)
                {
                        /* Should we complain if the unlink fails? */
                }
                free(fname);
        }
}

/*
 * Create a lockfile.
 *
 * filename is the name of the lockfile to create.
 * amPostmaster is used to determine how to encode the output PID.
 * isDDLock and refName are used to determine what error message to produce.
 */
static void
CreateLockFile(const char *filename, bool amPostmaster,
                           bool isDDLock, const char *refName)
{
        int                     fd;
        char            buffer[MAXPGPATH + 100];
        int                     ntries;
        int                     len;
        int                     encoded_pid;
        pid_t           other_pid;
        pid_t           my_pid = getpid();

        /*
         * 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)));
                }
                if ((len = read(fd, buffer, sizeof(buffer) - 1)) < 0)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not read lock file \"%s\": %m",
                                                        filename)));
                close(fd);

                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
                 *
                 * If the PID in the lockfile is our own PID or our parent's PID, then
                 * the file must be stale (probably left over from a previous system
                 * boot cycle).  We need this test because of the likelihood that a
                 * reboot will assign exactly the same PID as we had in the previous
                 * reboot.      Also, if there is just one more process launch in this
                 * reboot than in the previous one, the lockfile might mention our
                 * parent's PID.  We can reject that since we'd never be launched
                 * directly by a competing postmaster.  We can't detect grandparent
                 * processes unfortunately, 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.
                 *
                 * 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.)
                 *
                 * Windows hasn't got getppid(), but doesn't need it since it's not
                 * using real kill() either...
                 *
                 * Normally kill() will fail with ESRCH if the given PID doesn't
                 * exist.
                 */
                if (other_pid != my_pid
#ifndef WIN32
                        && other_pid != getppid()
#endif
                        )
                {
                        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.
                 */
                if (isDDLock)
                {
                        char       *ptr;
                        unsigned long id1,
                                                id2;

                        ptr = strchr(buffer, '\n');
                        if (ptr != NULL &&
                                (ptr = strchr(ptr + 1, '\n')) != NULL)
                        {
                                ptr++;
                                if (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.
         */
        snprintf(buffer, sizeof(buffer), "%d\n%s\n",
                         amPostmaster ? (int) my_pid : -((int) my_pid),
                         DataDir);
        errno = 0;
        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)));
        }
        if (close(fd))
        {
                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 for automatic removal of lockfile at proc_exit.
         */
        on_proc_exit(UnlinkLockFile, PointerGetDatum(strdup(filename)));
}

/*
 * 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.
 */
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)
{
        char            lockfile[MAXPGPATH];

        snprintf(lockfile, sizeof(lockfile), "%s.lock", socketfile);
        CreateLockFile(lockfile, amPostmaster, false, socketfile);
        /* Save name of lockfile for TouchSocketLockFile */
        strcpy(socketLockFile, lockfile);
}

/*
 * TouchSocketLockFile -- mark socket lock file as recently accessed
 *
 * This routine should be called every so often to ensure that the lock file
 * has a recent mod or access date.  That saves it
 * from being removed by overenthusiastic /tmp-directory-cleaner daemons.
 * (Another reason we should never have put the socket file in /tmp...)
 */
void
TouchSocketLockFile(void)
{
        /* Do nothing if we did not create a socket... */
        if (socketLockFile[0] != '\0')
        {
                /*
                 * 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 */
        }
}

/*
 * Append information about a shared memory segment to the data directory
 * lock file.
 *
 * This may be called multiple times in the life of a postmaster, if we
 * delete and recreate shmem due to backend crash.      Therefore, be prepared
 * to overwrite existing information.  (As of 7.1, a postmaster only creates
 * one shm seg at a time; but for the purposes here, if we did have more than
 * one then any one of them would do anyway.)
 */
void
RecordSharedMemoryInLockFile(unsigned long id1, unsigned long id2)
{
        int                     fd;
        int                     len;
        char       *ptr;
        char            buffer[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;
        }
        len = read(fd, buffer, sizeof(buffer) - 100);
        if (len < 0)
        {
                ereport(LOG,
                                (errcode_for_file_access(),
                                 errmsg("could not read from file \"%s\": %m",
                                                DIRECTORY_LOCK_FILE)));
                close(fd);
                return;
        }
        buffer[len] = '\0';

        /*
         * Skip over first two lines (PID and path).
         */
        ptr = strchr(buffer, '\n');
        if (ptr == NULL ||
                (ptr = strchr(ptr + 1, '\n')) == NULL)
        {
                elog(LOG, "bogus data in \"%s\"", DIRECTORY_LOCK_FILE);
                close(fd);
                return;
        }
        ptr++;

        /*
         * Append key information.      Format to try to keep it the same length
         * always (trailing junk won't hurt, but might confuse humans).
         */
        sprintf(ptr, "%9lu %9lu\n", id1, id2);

        /*
         * And rewrite the data.  Since we write in a single kernel call, this
         * update should appear atomic to onlookers.
         */
        len = strlen(buffer);
        errno = 0;
        if (lseek(fd, (off_t) 0, SEEK_SET) != 0 ||
                (int) write(fd, buffer, len) != len)
        {
                /* 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;
        }
        if (close(fd))
        {
                ereport(LOG,
                                (errcode_for_file_access(),
                                 errmsg("could not write to file \"%s\": %m",
                                                DIRECTORY_LOCK_FILE)));
        }
}


/*-------------------------------------------------------------------------
 *                              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,
                                file_minor;
        long            my_major = 0,
                                my_minor = 0;
        char       *endptr;
        const char *version_string = PG_VERSION;

        my_major = strtol(version_string, &endptr, 10);
        if (*endptr == '.')
                my_minor = strtol(endptr + 1, NULL, 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)));
        }

        ret = fscanf(file, "%ld.%ld", &file_major, &file_minor);
        if (ret != 2)
                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 || my_minor != file_minor)
                ereport(FATAL,
                                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                                 errmsg("database files are incompatible with server"),
                                 errdetail("The data directory was initialized by PostgreSQL version %ld.%ld, "
                                                   "which is not compatible with this version %s.",
                                                   file_major, file_minor, version_string)));
}

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

/*
 * GUC variables: lists of library names to be preloaded at postmaster
 * start and at backend start
 */
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;
        int                     elevel;
        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 identifiers */
        if (!SplitIdentifierString(rawstring, ',', &elemlist))
        {
                /* syntax error in list */
                pfree(rawstring);
                list_free(elemlist);
                ereport(LOG,
                                (errcode(ERRCODE_SYNTAX_ERROR),
                                 errmsg("invalid list syntax in parameter \"%s\"",
                                                gucname)));
                return;
        }

        /*
         * Choose notice level: avoid repeat messages when re-loading a library
         * that was preloaded into the postmaster.      (Only possible in EXEC_BACKEND
         * configurations)
         */
#ifdef EXEC_BACKEND
        if (IsUnderPostmaster && process_shared_preload_libraries_in_progress)
                elevel = DEBUG2;
        else
#endif
                elevel = LOG;

        foreach(l, elemlist)
        {
                char       *tok = (char *) lfirst(l);
                char       *filename;

                filename = pstrdup(tok);
                canonicalize_path(filename);
                /* If restricting, insert $libdir/plugins if not mentioned already */
                if (restricted && first_dir_separator(filename) == NULL)
                {
                        char       *expanded;

                        expanded = palloc(strlen("$libdir/plugins/") + strlen(filename) + 1);
                        strcpy(expanded, "$libdir/plugins/");
                        strcat(expanded, filename);
                        pfree(filename);
                        filename = expanded;
                }
                load_file(filename, restricted);
                ereport(elevel,
                                (errmsg("loaded library \"%s\"", filename)));
                pfree(filename);
        }

        pfree(rawstring);
        list_free(elemlist);
}

/*
 * 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_local_preload_libraries(void)
{
        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
}