如何增加更多 pty
     
1. 簡介
   由於 Phoenix BBS (Eagle BBS) 非 client/server 架構, 所有
   操作必須在 login pty 上. Sun-OS 可支援 256 ptys.
   此數字足夠正常使用. 但對於一些大站而言並不夠. 以下對 Sun-OS
   提供大於 256 pty 的作法:
   1. patch kernel
   2. 找尋 telnetd, rlogind source 並 patch 之.
   3. 利用多餘的 pty 加速 tty search.
      對於平常同時 login user 在 100 以上的站而言, tty search 是
      一項負擔. 假使有 100 個 on line user, 平均 一次成功 login 必須
      search 50 個 tty, 最差 100 次.
   

2. 以下介紹 patch Sun-OS kernel 之法. 由此將對 pty 有更深入
   了解. 
   
   Step 1. cd /sys/os
   -------
   sed -e 's/NPTY/NNTY/g' -e 's/pty\.h/nty\.h/g' \
       -e 's/pty_softc/nty_softc/g' -e 's/npty/nnty/g' \
       tty_ptyconf.c > tty_ntyconf.c

   Step 2. cd /sys/sun, edit conf.c, 
   -------
   add the following lines before the array "struct cdevsw   cdevsw[]".
#include "nty.h"
#if NNTY > 0
extern struct streamtab ntsinfo;
extern int ntcopen(), ntcclose(), ntcread(), ntcwrite(), ntcioctl();
extern int ntcselect();
#define ntstab      &ntsinfo
#else
#define ntstab      0
#define ntcopen     nodev
#define ntcclose    nodev
#define ntcread     nodev
#define ntcwrite    nodev
#define ntcioctl    nodev
#define ntcselect   nodev
#endif

   add more array element to "struct cdevsw   cdevsw[]". I suggest to 
use element "108" and "109" 
(they will be the major number of the extra tty and pty pair).

    ,
    {
        nodev,          nodev,          nodev,          nodev,          /*108*/
        nodev,          nodev,          nodev,          0,
        ntstab,     0,
    },
    {
        ntcopen,    ntcclose,           ntcread,        ntcwrite,       /*109*/
        ntcioctl,   nulldev,            ntcselect,  0,
        0,              0,
    }


 Step 3. 
 -------
 cd /sys/`arch -k`/OBJ
 sed 's/NPTY/NNTY/g' pty.h > nty.h
 perl -p -e 's/_ptsinfo/_ntsinfo/g;' -e 's/_ptc/_ntc/g;' \
         -e 's/_pty_softc/_nty_softc/g' tty_pty.o > tty_nty.o
         

 Step 4.
 -------
 add the following line to /sys/conf.common/files.cmn
os/tty_nty.c            optional nty
os/tty_ntyconf.c        optional nty

 Step 5.
 -------
 cd /sys/`arch -k`/conf
 cp GENERIC BBS-NTY
 add the following line to BBS-NTY
pseudo-device   nty256          # pseudo-tty's, also needed for SunView
 if you find the line
pseudo-device   pty          # pseudo-tty's, also needed for SunView
 change it into
pseudo-device   pty256          # pseudo-tty's, also needed for SunView
 當然, 至少, 加
maxusers    ??         
 into
maxusers    64         


 Step 6.
 -------
 cd /sys/`arch -k`/conf
 set path=(/bin /usr/etc $path)
 config BBS-NTY 
 cd ../BBS-NTY
 cat pty.h nty.h  
 (make sure their value are 256)
 make depend 
 make
 mv /vmunix /vmunix.orig
 cp vmunix /
 fastboot

 Step 7.0, make sure you have made the first set of 256 PTYs by
 --------
/dev/MAKEDEV pty4
/dev/MAKEDEV pty5
....
/dev/MAKEDEV pty15

 Step 7, run the following perl script
 -------
#!/usr/local/bin/perl
open(NTAB,"> /tmp/ttytab") || die "can't write /tmp/ttytab $!\n";
$ttys = "klmonKLMNOUVWXYZ";
@ttys = split(/ */, $ttys);
chdir('/dev');
$offset = 0;
foreach $tty (@ttys) {
  for ($i=0;$i<16;$i++) {
    $tname = sprintf("tty${tty}%x",$i);
    $pname = sprintf("pty${tty}%x",$i);
    print NTAB "$tname   none                            network  off secure\n";
    system("/usr/etc/mknod $tname c 108 $offset");
    system("/usr/etc/mknod $pname c 109 $offset");
    $offset ++;
  }
}
close(NTAB);


cat /tmp/ttytab >> /etc/ttytab


 Step 8, modify and recompile all commands which will use pty 
 -------
         by changing a line with the string
"pqrstuvwxyzPQRST" 
   into
"klmnopqrstuvwxyzKLMNOPQRSTUVWXYZ" 

你必須至少重新 compile rlogind, telnetd 以使用多出的 pty/tty pair.
其它相關使用 pty 者有, screen, script, xterm 等.


  1.x 用 loadmod 之探討. 
    以上用 patch kernel 之法, 應該也可改為用 loadmod, 而無須 patch kernel.
    在此略過. (需要一 wrapper, 一 script for making device )    
    
--------------------------------------------------------------------
3. telnetd/rlogind source in the public domain
   建議使用
   1. logdaemon  (ftp.csie.nctu.edu.tw:/pub/security/logdaemon-2.tar.gz)    
   2. NetBSD telnetd/rlogind source. (netbsd.csie.nctu.edu.tw:/pub/...)
   其中 logdaemon 特別有考慮 tty security 問題.
---------------------------------------------------------------------    
4. 利用多餘之 pty 加速 tty search
   中央 Totoro 和 交大資科 CIS BBS 都已增加到大於 512 組 tty/pty, 現在
   面臨的新問題是 login 人數多時,  tty search 速度將變得很慢, 
   若使用下列簡單的 hashing 方法, 將使 tty/pty pairs 越多
   則 tty search 越快:
   取 time 做 hash key, 假設有 512 組 tty
 
time_t now;
int i,j,p,last;
 
time(&now);
now %= 512;
for (i = now ; i < now + 512 ; ++i) {
        line = "/dev/ptyXX";
        line[strlen("/dev/pty")] = "klmnopqrstuvwxyzKLMNOPQRSTUVWXYZ"[i %  32];
        line[strlen("/dev/ptyp")] = "0123456789abcdef"[(i%512)/32];
        if ((p = open(line, O_RDWR)) == -1)
               continue;
         ...............                                 
}
 
 則第 0-512 秒 login 之 user 將可望在第一次 search 即 hit.
 tty 數越多 hit 機率越高.