pg_tablespace.c

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/*-------------------------------------------------------------------------
 *
 * pg_tablespace.c
 *    routines to support manipulation of the pg_tablespace relation
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/catalog/pg_tablespace.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <unistd.h>
#include <sys/stat.h>
 
#include "catalog/pg_tablespace.h"
#include "commands/tablespace.h"
#include "miscadmin.h"
 
 
/*
 * get_tablespace_location
 *      Get a tablespace's location as a C-string, by its OID
 */
char *
get_tablespace_location(Oid tablespaceOid)
{
    char        sourcepath[MAXPGPATH];
    char        targetpath[MAXPGPATH];
    int         rllen;
    struct stat st;
 
    /*
     * It's useful to apply this to pg_class.reltablespace, wherein zero means
     * "the database's default tablespace".  So, rather than throwing an error
     * for zero, we choose to assume that's what is meant.
     */
    if (tablespaceOid == InvalidOid)
        tablespaceOid = MyDatabaseTableSpace;
 
    /*
     * Return empty string for the cluster's default tablespaces
     */
    if (tablespaceOid == DEFAULTTABLESPACE_OID ||
        tablespaceOid == GLOBALTABLESPACE_OID)
        return pstrdup("");
 
    /*
     * Find the location of the tablespace by reading the symbolic link that
     * is in pg_tblspc/<oid>.
     */
    snprintf(sourcepath, sizeof(sourcepath), "%s/%u", PG_TBLSPC_DIR, tablespaceOid);
 
    /*
     * Before reading the link, check if the source path is a link or a
     * junction point.  Note that a directory is possible for a tablespace
     * created with allow_in_place_tablespaces enabled.  If a directory is
     * found, a relative path to the data directory is returned.
     */
    if (lstat(sourcepath, &st) < 0)
        ereport(ERROR,
                errcode_for_file_access(),
                errmsg("could not stat file \"%s\": %m",
                       sourcepath));
 
    if (!S_ISLNK(st.st_mode))
        return pstrdup(sourcepath);
 
    /*
     * In presence of a link or a junction point, return the path pointed to.
     */
    rllen = readlink(sourcepath, targetpath, sizeof(targetpath));
    if (rllen < 0)
        ereport(ERROR,
                errcode_for_file_access(),
                errmsg("could not read symbolic link \"%s\": %m",
                       sourcepath));
    if (rllen >= sizeof(targetpath))
        ereport(ERROR,
                errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                errmsg("symbolic link \"%s\" target is too long",
                       sourcepath));
    targetpath[rllen] = '\0';
 
    return pstrdup(targetpath);
}