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 09:42:26 -0400

 On Fri, 23 Sep 2011 13:30:06 +0000 (UTC)
 Matthew Mondor <mm_lists%pulsar-zone.net@localhost> wrote:
 
 >  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
 
 >  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
 
 Oh, another particularity is that there also appear to be lost bytes at
 the end; On Linux there is a last smaller read to fill in the missing
 bytes.  The larger the buffer size the more bytes are lost in our case.
 
 Thanks,
 -- 
 Matt