relpath.c

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/*-------------------------------------------------------------------------
 * relpath.c
 *      Shared frontend/backend code to compute pathnames of relation files
 *
 * This module also contains some logic associated with fork names.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/common/relpath.c
 *
 *-------------------------------------------------------------------------
 */
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
#include "catalog/pg_tablespace_d.h"
#include "common/relpath.h"
#include "storage/procnumber.h"
 
 
/*
 * Lookup table of fork name by fork number.
 *
 * If you add a new entry, remember to update the errhint in
 * forkname_to_number() below, and update the SGML documentation for
 * pg_relation_size().
 */
const char *const forkNames[] = {
    [MAIN_FORKNUM] = "main",
    [FSM_FORKNUM] = "fsm",
    [VISIBILITYMAP_FORKNUM] = "vm",
    [INIT_FORKNUM] = "init",
};
 
StaticAssertDecl(lengthof(forkNames) == (MAX_FORKNUM + 1),
                 "array length mismatch");
 
/*
 * forkname_to_number - look up fork number by name
 *
 * In backend, we throw an error for no match; in frontend, we just
 * return InvalidForkNumber.
 */
ForkNumber
forkname_to_number(const char *forkName)
{
    ForkNumber  forkNum;
 
    for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
        if (strcmp(forkNames[forkNum], forkName) == 0)
            return forkNum;
 
#ifndef FRONTEND
    ereport(ERROR,
            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
             errmsg("invalid fork name"),
             errhint("Valid fork names are \"main\", \"fsm\", "
                     "\"vm\", and \"init\".")));
#endif
 
    return InvalidForkNumber;
}
 
/*
 * forkname_chars
 *      We use this to figure out whether a filename could be a relation
 *      fork (as opposed to an oddly named stray file that somehow ended
 *      up in the database directory).  If the passed string begins with
 *      a fork name (other than the main fork name), we return its length,
 *      and set *fork (if not NULL) to the fork number.  If not, we return 0.
 *
 * Note that the present coding assumes that there are no fork names which
 * are prefixes of other fork names.
 */
int
forkname_chars(const char *str, ForkNumber *fork)
{
    ForkNumber  forkNum;
 
    for (forkNum = 1; forkNum <= MAX_FORKNUM; forkNum++)
    {
        int         len = strlen(forkNames[forkNum]);
 
        if (strncmp(forkNames[forkNum], str, len) == 0)
        {
            if (fork)
                *fork = forkNum;
            return len;
        }
    }
    if (fork)
        *fork = InvalidForkNumber;
    return 0;
}
 
 
/*
 * GetDatabasePath - construct path to a database directory
 *
 * Result is a palloc'd string.
 *
 * XXX this must agree with GetRelationPath()!
 */
char *
GetDatabasePath(Oid dbOid, Oid spcOid)
{
    if (spcOid == GLOBALTABLESPACE_OID)
    {
        /* Shared system relations live in {datadir}/global */
        Assert(dbOid == 0);
        return pstrdup("global");
    }
    else if (spcOid == DEFAULTTABLESPACE_OID)
    {
        /* The default tablespace is {datadir}/base */
        return psprintf("base/%u", dbOid);
    }
    else
    {
        /* All other tablespaces are accessed via symlinks */
        return psprintf("%s/%u/%s/%u",
                        PG_TBLSPC_DIR, spcOid,
                        TABLESPACE_VERSION_DIRECTORY, dbOid);
    }
}
 
/*
 * GetRelationPath - construct path to a relation's file
 *
 * The result is returned in-place as a struct, to make it suitable for use in
 * critical sections etc.
 *
 * Note: ideally, procNumber would be declared as type ProcNumber, but
 * relpath.h would have to include a backend-only header to do that; doesn't
 * seem worth the trouble considering ProcNumber is just int anyway.
 */
RelPathStr
GetRelationPath(Oid dbOid, Oid spcOid, RelFileNumber relNumber,
                int procNumber, ForkNumber forkNumber)
{
    RelPathStr  rp;
 
    if (spcOid == GLOBALTABLESPACE_OID)
    {
        /* Shared system relations live in {datadir}/global */
        Assert(dbOid == 0);
        Assert(procNumber == INVALID_PROC_NUMBER);
        if (forkNumber != MAIN_FORKNUM)
            sprintf(rp.str, "global/%u_%s",
                    relNumber, forkNames[forkNumber]);
        else
            sprintf(rp.str, "global/%u",
                    relNumber);
    }
    else if (spcOid == DEFAULTTABLESPACE_OID)
    {
        /* The default tablespace is {datadir}/base */
        if (procNumber == INVALID_PROC_NUMBER)
        {
            if (forkNumber != MAIN_FORKNUM)
            {
                sprintf(rp.str, "base/%u/%u_%s",
                        dbOid, relNumber,
                        forkNames[forkNumber]);
            }
            else
                sprintf(rp.str, "base/%u/%u",
                        dbOid, relNumber);
        }
        else
        {
            if (forkNumber != MAIN_FORKNUM)
                sprintf(rp.str, "base/%u/t%d_%u_%s",
                        dbOid, procNumber, relNumber,
                        forkNames[forkNumber]);
            else
                sprintf(rp.str, "base/%u/t%d_%u",
                        dbOid, procNumber, relNumber);
        }
    }
    else
    {
        /* All other tablespaces are accessed via symlinks */
        if (procNumber == INVALID_PROC_NUMBER)
        {
            if (forkNumber != MAIN_FORKNUM)
                sprintf(rp.str, "%s/%u/%s/%u/%u_%s",
                        PG_TBLSPC_DIR, spcOid,
                        TABLESPACE_VERSION_DIRECTORY,
                        dbOid, relNumber,
                        forkNames[forkNumber]);
            else
                sprintf(rp.str, "%s/%u/%s/%u/%u",
                        PG_TBLSPC_DIR, spcOid,
                        TABLESPACE_VERSION_DIRECTORY,
                        dbOid, relNumber);
        }
        else
        {
            if (forkNumber != MAIN_FORKNUM)
                sprintf(rp.str, "%s/%u/%s/%u/t%d_%u_%s",
                        PG_TBLSPC_DIR, spcOid,
                        TABLESPACE_VERSION_DIRECTORY,
                        dbOid, procNumber, relNumber,
                        forkNames[forkNumber]);
            else
                sprintf(rp.str, "%s/%u/%s/%u/t%d_%u",
                        PG_TBLSPC_DIR, spcOid,
                        TABLESPACE_VERSION_DIRECTORY,
                        dbOid, procNumber, relNumber);
        }
    }
 
    Assert(strnlen(rp.str, REL_PATH_STR_MAXLEN + 1) <= REL_PATH_STR_MAXLEN);
 
    return rp;
}