On Sep 11, 3:02pm, Corinna Vinschen wrote:
-- Subject: Re: [Fwd: 1.5.11-1: sftp performance problem]
>
> http://cygwin.com/acronyms/#PCYMTNQREAIYR
Sorry ... done.
> | One really annoying consequence of socketpairs for sshd is that
> | Windows-native (i.e. non-Cygwin) programs don't know how to write
> | directly to sockets on stdout (or stderr), so if you try to use
> | them via ssh, their output silently disappears.
>
> Oh lord! I tried it with `net', `ping' and `nslookup', which are roughly
> the only Windows applications I use on the command line, and all three
> have no problems. I'm wondering how the above can happen since the
> interactive application side is running in a PTY (which *is* a pipe),
> not on socketpairs.
Try it without a pty:
ssh cygwin-system-with-sshd-using-sockpairs "win32-native-command"
vs.
ssh cygwin-system-with-sshd-using-sockpairs "win32-native-command | cat"
> | I think OpenSSH uses pipes on most platforms by default, so I'm also
>
> Only on those platforms which have known problems with (or no implementation
> of) socketpairs.
OK, maybe I am misremembering, or the default changed ages ago.
I see that sshd on Linux uses socketpairs.
> | somewhat concerned that the socketpair-specific code in OpenSSH might be
> | a bit crufty.
>
> Why? Socketpairs are in the same shape as any other socket connection
> since they are using the same code. And I surely do care for socket
> operations. See the ChangeLogs. What especially do you think is "crufty"?
>
-- End of excerpt from Corinna Vinschen
My concern was about the state of the OpenSSH code base, not Cygwin, and
it was just a vague fear, based on the previous (I guess now incorrect)
[mis]understanding that OpenSSH prefers to use pipes.
> | It's not obvious to me why socketpairs would be inherently faster
> | than pipes.
It occurred to me after I wrote this that if no pipes were used at all,
then the select_pipe thread would not be spawned ... the select_socket
thread would handle everything. This might be win, but we'd need to
measure to see if the effect is significant.
And we'd still have the problem with win32-native apps, which I think
is a show-stopper for socketpairs.
--
Bob
