Re: kern/45352: pty(4)/tty(4) have a 1024 bytes transfer limit

[Matthew Mondor <mm_lists%pulsar-zone.net@localhost>]

The following reply was made to PR kern/45352; it has been noted by GNATS.

From: Matthew Mondor <mm_lists%pulsar-zone.net@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/45352: pty(4)/tty(4) have a 1024 bytes transfer limit
Date: Sun, 18 Sep 2011 07:23:08 -0400

 On Mon, 12 Sep 2011 07:25:02 +0000 (UTC)
 Matthew Mondor <mm_lists%pulsar-zone.net@localhost> wrote:
 
 >  Yesterday night I looked at porting it to netbsd-5 but the code seemed
 >  quite different (netbsd-5 getting old?), so it'll probably be less
 >  trouble to build a -current kernel to try it on.  I should be able to
 >  do this before the weekend.
 
 I had the opportunity to build a -current kernel with the applied patch
 and to do some tests.
 
 Unfortunately, a 1024 limit still exists.  I first tried my unmodified
 code with the new sysctl set at 4096, with an MTU of 3000.  To make
 sure that it wasn't a limitation of PPP, I also did tests using dd,
 while ktraceing the process.  It indeed still shows reads of 1024 bytes
 at a time.
 
 I then also tried using the new ioctl(2) rather than the sysctl knob,
 and noticed that the request macro names seemed inversed.  So using the
 TIOCGQSIZE one instead of the TIOCSQSIZE one, there was no EINVAL, but
 still again the tests with dd showed a 1024 bytes limit.
 
 The following example shows an attempt to read 3168 bytes.
 dd pushes a 3168 bytes block, but 1024 bytes are read:
 
   1368      1 tty-udp  CALL  read(3,0xbb903000,0xc60)
   1368      1 tty-udp  GIO   fd 3 read 1024 bytes
         000   00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 ................
         ***
         3f0   00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 ................
   1368      1 tty-udp  RET   read 1024/0x400
 
 Thanks again,
 -- 
 Matt