so-called-hang-on-exit

[Jani Jaakkola]

On Wed, 31 Jul 2002, Markus Friedl wrote:

> so, should this go into 3.5?

I vote no, it should not. Here is why:
 
> +	/* allow data loss on pty */

And it indeed happens. After applying this patch, if I say 
'ssh -t localhost pico' and then exit pico I get a garbled screen. 
Picos screen clearing and terminal attribute resetting escape 
sequences are lost because of allowing data loss on pty (pico is just an 
example. I guess most tty programs will behave the same.).

Here is another example (my test sshd lives behind port 444):

<CLIP>
$ ssh -t localhost -p 444 exec echo blah
blah
Connection to localhost closed.
$ ssh -t localhost -p 444 exec echo blah
Connection to localhost closed.
$ ssh -t localhost -p 444 exec echo blah
blah
</CLIP>

So sometimes just 'echo blah' is lost.

My suggestion is that instead of just closing the channel when the 
session process dies, sshd should effort to empty the pty buffer before 
closing the channel. This could be implemented so that 
when the session process dies, sshd should read (and buffer) the pty 
master data until it gets EAGAIN and then close the channel. All 
pending output from dead session processes should allready be in the pty 
buffer, so first EAGAIN means that all of it has been read processed.

I guess I will attempt to implement this, but it will take some time (I 
will need to learn how session.c and serverloop.c work first).

- Jani