Re: Pty is losing bytes

["Alan Curry" <pacman-kernel@manson.clss.net>]

Linus Torvalds writes the following:
>
>Does the problem go away if you change the default value of "chunk" (in 
>drivers/char/tty_io.c:do_tty_write) from 4096 to 2048? If so, that means 
>that the pty code has _claimed_ to have written 4kB, and only ever wrote 
>4kB-1 bytes. That in turn implies that "ldisc.receive_room()" disagrees 
>with "ldisc.receive_buf()".
>

That does fix it for me, in 2.6.10-as3 (the -as3 patch doesn't touch anything
near the pty code, so it should be good for vanilla 2.6.10 too).

I noticed while testing that the "lost byte" is occasionally more than one
byte. It's always one byte at the 4k mark, but sometimes a larger group of
bytes is lost around the 8k mark, and (more rarely) an even larger group of
bytes is lost at the 12k mark.

$ ls -l /etc/mime.types
-rw-r--r--    1 root     root        15723 Apr  9  2002 /etc/mime.types
$ while :; do ./ptytest < /etc/mime.types | wc -c ; sleep 1 ; done
  15722
  15710
  15722
  15710
  15722
  15710
  15722
  15722
  15682
(and so on)