DBM.new

static VALUE
fdbm_initialize(int argc, VALUE *argv, VALUE obj)
{
    VALUE file, vmode, vflags;
    DBM *dbm;
    struct dbmdata *dbmp;
    int mode, flags = 0;

    TypedData_Get_Struct(obj, struct dbmdata, &dbm_type, dbmp);
    if (rb_scan_args(argc, argv, "12", &file, &vmode, &vflags) == 1) {
        mode = 0666;           /* default value */
    }
    else if (NIL_P(vmode)) {
        mode = -1;             /* return nil if DB not exist */
    }
    else {
        mode = NUM2INT(vmode);
    }

    if (!NIL_P(vflags))
        flags = NUM2INT(vflags);

    FilePathValue(file);

    /*
     * Note:
     * gdbm 1.10 works with O_CLOEXEC.  gdbm 1.9.1 silently ignore it.
     */
#ifndef O_CLOEXEC
#   define O_CLOEXEC 0
#endif

    if (flags & RUBY_DBM_RW_BIT) {
        flags &= ~RUBY_DBM_RW_BIT;
        dbm = dbm_open(RSTRING_PTR(file), flags|O_CLOEXEC, mode);
    }
    else {
        dbm = 0;
        if (mode >= 0) {
            dbm = dbm_open(RSTRING_PTR(file), O_RDWR|O_CREAT|O_CLOEXEC, mode);
        }
        if (!dbm) {
            dbm = dbm_open(RSTRING_PTR(file), O_RDWR|O_CLOEXEC, 0);
        }
        if (!dbm) {
            dbm = dbm_open(RSTRING_PTR(file), O_RDONLY|O_CLOEXEC, 0);
        }
    }

    if (dbm) {
        /*
         * History of dbm_pagfno() and dbm_dirfno() in ndbm and its compatibles.
         * (dbm_pagfno() and dbm_dirfno() is not standardized.)
         *
         * 1986: 4.3BSD provides ndbm.
         *       It provides dbm_pagfno() and dbm_dirfno() as macros.
         * 1991: gdbm-1.5 provides them as functions.
         *       They returns a same descriptor.
         *       (Earlier releases may have the functions too.)
         * 1991: Net/2 provides Berkeley DB.
         *       It doesn't provide dbm_pagfno() and dbm_dirfno().
         * 1992: 4.4BSD Alpha provides Berkeley DB with dbm_dirfno() as a function.
         *       dbm_pagfno() is a macro as DBM_PAGFNO_NOT_AVAILABLE.
         * 1997: Berkeley DB 2.0 is released by Sleepycat Software, Inc.
         *       It defines dbm_pagfno() and dbm_dirfno() as macros.
         * 2011: gdbm-1.9 creates a separate dir file.
         *       dbm_pagfno() and dbm_dirfno() returns different descriptors.
         */
#if defined(HAVE_DBM_PAGFNO)
        rb_fd_fix_cloexec(dbm_pagfno(dbm));
#endif
#if defined(HAVE_DBM_DIRFNO)
        rb_fd_fix_cloexec(dbm_dirfno(dbm));
#endif

#if defined(RUBYDBM_DB_HEADER) && defined(HAVE_TYPE_DBC)
        /* Disable Berkeley DB error messages such as:
         * DB->put: attempt to modify a read-only database */
        ((DBC*)dbm)->dbp->set_errfile(((DBC*)dbm)->dbp, NULL);
#endif
    }

    if (!dbm) {
        if (mode == -1) return Qnil;
        rb_sys_fail_str(file);
    }

    if (dbmp->di_dbm)
        dbm_close(dbmp->di_dbm);
    dbmp->di_dbm = dbm;
    dbmp->di_size = -1;

    return obj;
}