pty behaviour

Hi,

I figured out why screen doesn't support cut&paste of more than 300
characters.  This is the high watermark in term.

The pty_io_write implementation drops (flushes) all input if the queue
is suspended (qavail returns 0).  This will be the case when the high
watermark is reached.  Thus, if screen uses a single write to its pty
end when the text is pasted, only up to the first 300 characters are
written.

pty_io_write does in particular not suspend the write, wait on the
queue condition and continue after the queue is drained below the low
watermark and unsuspended.

I couldn't find a description of what pty's are supposed to do on
read/write.  However, screen seems to expect to be able to do it, and
screen is widely ported.  Actually, I tried to find out what screen is
trying to do (ie if it splits up the input in chunks etc), but the
code is a horrid mess (it's slowpaste option worked, though, IIRC, as
it sends input char by char).  Likewise I saw a perl pty test fail due
to this.

So, is there anything I am missing?  Shouldn't we implement
pty_io_write as any other writer, with suspending behaviour unless
O_NONBLOCK is set (if that is even possible for a pty)?

Thanks,
Marcus