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: Fri, 23 Sep 2011 09:25:57 -0400

 So I wrote a small test program and imported it into my public CVS tree
 at:
 
http://cvs.pulsar-zone.net/cgi-bin/cvsweb.cgi/mmondor/tests/pty-test/pty-test.c?rev=1.3;content-type=text%2Fplain
 
 I would be glad to fix it if there's something I'm missing.  However:
 
 
 NetBSD-5 with -s 512: fine
 
 parent: started; opening PTY and spawning child
 parent: sleeping to make sure child is ready
 child: started; open "/dev/pts/11"
 child: TTY open, starting read loop
 child: polling
 parent: writing
 parent: attempting to write 512 bytes to PTY
 child: attempting to read 512 bytes
 child: read 512 bytes from TTY
 child: attempting to read 512 bytes
 child: polling
 parent: wrote 512 bytes to PTY
 parent: attempting to write 512 bytes to PTY
 child: attempting to read 512 bytes
 child: read 512 bytes from TTY
 child: attempting to read 512 bytes
 child: polling
 parent: wrote 512 bytes to PTY
 parent: waiting for child to exit
 child: closing TTY
 child: exiting
 parent: closing PTY
 parent: exiting
 
 NetBSD-5 with -s 1024: reaches a 1022 bytes read limit
 
 parent: started; opening PTY and spawning child
 parent: sleeping to make sure child is ready
 child: started; open "/dev/pts/11"
 child: TTY open, starting read loop
 child: polling
 parent: writing
 parent: attempting to write 1024 bytes to PTY
 child: attempting to read 1024 bytes
 parent: wrote 1024 bytes to PTY
 parent: attempting to write 1024 bytes to PTY
 child: read 1022 bytes from TTY
 child: attempting to read 1024 bytes
 parent: wrote 1024 bytes to PTY
 parent: waiting for child to exit
 child: read 1022 bytes from TTY
 child: attempting to read 1024 bytes
 child: polling
 child: closing TTY
 child: exiting
 parent: closing PTY
 parent: exiting
 
 NetBSD-5 with -s 2048: still hits the 1022 bytes read limit
 
 parent: started; opening PTY and spawning child
 parent: sleeping to make sure child is ready
 child: started; open "/dev/pts/11"
 child: TTY open, starting read loop
 child: polling
 parent: writing
 parent: attempting to write 2048 bytes to PTY
 child: attempting to read 2048 bytes
 child: read 1022 bytes from TTY
 child: attempting to read 2048 bytes
 parent: wrote 2048 bytes to PTY
 parent: attempting to write 2048 bytes to PTY
 child: read 1022 bytes from TTY
 child: attempting to read 2048 bytes
 child: read 1022 bytes from TTY
 child: attempting to read 2048 bytes
 parent: wrote 2048 bytes to PTY
 parent: waiting for child to exit
 child: read 1022 bytes from TTY
 child: attempting to read 2048 bytes
 child: polling
 child: closing TTY
 child: exiting
 parent: closing PTY
 parent: exiting
 
 
 Linux with -s 512: fine
 
 parent: started; opening PTY and spawning child
 parent: sleeping to make sure child is ready
 child: started; open "/dev/pts/8"
 child: TTY open, starting read loop
 child: polling
 parent: writing
 parent: attempting to write 512 bytes to PTY
 parent: wrote 512 bytes to PTY
 parent: attempting to write 512 bytes to PTY
 parent: wrote 512 bytes to PTY
 parent: waiting for child to exit
 child: attempting to read 512 bytes
 child: read 512 bytes from TTY
 child: attempting to read 512 bytes
 child: read 512 bytes from TTY
 child: attempting to read 512 bytes
 child: polling
 child: closing TTY
 child: exiting
 parent: closing PTY
 parent: exiting
 
 Linux with -s 2048: fine
 
 parent: started; opening PTY and spawning child
 parent: sleeping to make sure child is ready
 child: started; open "/dev/pts/8"
 child: TTY open, starting read loop
 child: polling
 parent: writing
 parent: attempting to write 2048 bytes to PTY
 parent: wrote 2048 bytes to PTY
 parent: attempting to write 2048 bytes to PTY
 parent: wrote 2048 bytes to PTY
 parent: waiting for child to exit
 child: attempting to read 2048 bytes
 child: read 2048 bytes from TTY
 child: attempting to read 2048 bytes
 child: read 2048 bytes from TTY
 child: attempting to read 2048 bytes
 child: polling
 child: closing TTY
 child: exiting
 parent: closing PTY
 parent: exiting
 
 Linux with -s 4096: reaches a 4095 bytes read limit
 
 parent: started; opening PTY and spawning child
 parent: sleeping to make sure child is ready
 child: started; open "/dev/pts/8"
 child: TTY open, starting read loop
 child: polling
 parent: writing
 parent: attempting to write 4096 bytes to PTY
 parent: wrote 4096 bytes to PTY
 parent: attempting to write 4096 bytes to PTY
 parent: wrote 4096 bytes to PTY
 parent: waiting for child to exit
 child: attempting to read 4096 bytes
 child: read 4095 bytes from TTY
 child: attempting to read 4096 bytes
 child: read 4095 bytes from TTY
 child: attempting to read 4096 bytes
 child: read 2 bytes from TTY
 child: attempting to read 4096 bytes
 child: polling
 child: closing TTY
 child: exiting
 parent: closing PTY
 parent: exiting
 
 Linux with -s 8192: still hits the 4095 bytes read limit
 
 parent: started; opening PTY and spawning child
 parent: sleeping to make sure child is ready
 child: started; open "/dev/pts/8"
 child: TTY open, starting read loop
 child: polling
 parent: writing
 parent: attempting to write 8192 bytes to PTY
 parent: wrote 8192 bytes to PTY
 parent: attempting to write 8192 bytes to PTY
 parent: wrote 8192 bytes to PTY
 parent: waiting for child to exit
 child: attempting to read 8192 bytes
 child: read 4095 bytes from TTY
 child: attempting to read 8192 bytes
 child: read 4095 bytes from TTY
 child: attempting to read 8192 bytes
 child: read 4095 bytes from TTY
 child: attempting to read 8192 bytes
 child: read 4095 bytes from TTY
 child: attempting to read 8192 bytes
 child: read 4 bytes from TTY
 child: attempting to read 8192 bytes
 child: polling
 child: closing TTY
 child: exiting
 parent: closing PTY
 parent: exiting
 
 
 I did not test this program with the patch Christos proposed against
 -current yet (although I did test the some days ago using a pty-udp
 tunnel without much success, but I yet have to try with 8192 as
 suggested by Darren).  When I can I'll boot again the -current kernel
 and also run this test on it.
 
 Thanks,
 -- 
 Matt