PostgreSQL在何处处理 sql查询之十九

/*
 * open a file in an arbitrary directory
 *
 * NB: if the passed pathname is relative (which it usually is),
 * it will be interpreted relative to the process' working directory
 * (which should always be $PGDATA when this code is running).
 */
File
PathNameOpenFile(FileName fileName, int fileFlags, int fileMode)
{
    char       *fnamecopy;
    File        file;
    Vfd           *vfdP;

    DO_DB(elog(LOG, "PathNameOpenFile: %s %x %o",
               fileName, fileFlags, fileMode));
    /*
     * We need a malloc'd copy of the file name; fail cleanly if no room.
     */
    fnamecopy = strdup(fileName);
    if (fnamecopy == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));

    file = AllocateVfd();
    vfdP = &VfdCache[file];

    while (nfile + numAllocatedDescs >= max_safe_fds)
    {
        if (!ReleaseLruFile())
            break;
    }

    vfdP->fd = BasicOpenFile(fileName, fileFlags, fileMode);

    if (vfdP->fd < 0)
    {
        FreeVfd(file);
        free(fnamecopy);
        return -1;
    }
    ++nfile;
    DO_DB(elog(LOG, "PathNameOpenFile: success %d",
               vfdP->fd));

    Insert(file);
    /**
    fprintf(stderr,"(O_CREAT) is:%x \n",O_CREAT);
    fprintf(stderr,"(O_TRUNC) is:%x \n",O_TRUNC);
    fprintf(stderr,"(O_EXCL) is:%x \n",O_EXCL);
    fprintf(stderr,"(O_CREAT | O_TRUNC | O_EXCL) is: %x\n", (O_CREAT | O_TRUNC | O_EXCL));
    fprintf(stderr,"~(O_CREAT | O_TRUNC | O_EXCL) is: %x\n", ~(O_CREAT | O_TRUNC | O_EXCL));
    fprintf(stderr,"fileFlags is %x\n", fileFlags);
    fprintf(stderr,"fileFlags & ~(O_CREAT | O_TRUNC | O_EXCL) is %x\n", fileFlags & ~(O_CREAT | O_TRUNC | O_EXCL));
    */

    vfdP->fileName = fnamecopy;
    /* Saved flags are adjusted to be OK for re-opening file */
    vfdP->fileFlags = fileFlags & ~(O_CREAT | O_TRUNC | O_EXCL);
    vfdP->fileMode = fileMode;
    vfdP->seekPos = 0;
    vfdP->fileSize = 0;
    vfdP->fdstate = 0x0;
    vfdP->resowner = NULL;

    //fprintf(stderr,"file is: %d by proces %d \n\n",file,getpid());

    return file;
}