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Date: Thu, 8 Aug 2002 16:18:59 +0400
From: egor duda <deo AT logos-m DOT ru>
Reply-To: egor duda <cygwin AT cygwin DOT com>
Organization: deo
X-Priority: 3 (Normal)
Message-ID: <168935202570.20020808161859@logos-m.ru>
To: Laurent Pinchart <laurent DOT pinchart AT capflow DOT com>
CC: cygwin AT cygwin DOT com
Subject: Re: OpenSSH and WinCVS in Windows 9x
In-Reply-To: <200208081356.37427.laurent.pinchart@capflow.com>
References: <20020806140534 DOT 757a155a DOT steven DOT obrien2 AT ntlworld DOT com>
 <200208081138 DOT 11412 DOT laurent DOT pinchart AT capflow DOT com>
 <124926316162 DOT 20020808135052 AT logos-m DOT ru>
 <200208081356 DOT 37427 DOT laurent DOT pinchart AT capflow DOT com>
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Hi!

Thursday, 08 August, 2002 Laurent Pinchart laurent DOT pinchart AT capflow DOT com wrote:

LP> WinCVS creates the ssh process by calling CreateProcess, which has stdin and
LP> stdout redirected to pipes. The pipes are then converted to C file 
LP> descriptors, which in turn are converted to FILE pointers. Closing those 
LP> FILEs doesn't make ssh terminate.

LP> I tried to modify the WinCVS code, and closed all the pipe handles right after 
LP> creating the child process (ssh). This doesn't make the child process 
LP> terminate.

LP> I suppose that it is then a bug in OpenSSH/Cygwin. I'll try to investigate in 
LP> the OpenSSH sources. My guess is that OpenSSH calls select() on the standard 
LP> input, and fails to detect that the pipe has been closed. Once again, this 
LP> only occurs in Win98, not in Win2k.

Cygwin uses the following code to periodically probe pipe status:

(file select.cc)
static int
peek_pipe (select_record *s, bool from_select)
...
else if (!PeekNamedPipe (h, NULL, 0, NULL, (DWORD *) &n, NULL))
   {
     select_printf ("%s, PeekNamedPipe failed, %E", fh->get_name ());
     n = -1;
   }
...

Peeking into pipe for zero bytes is quite unusual, so win98 may return
something wrong here. You can probably attach with a debugger or strace
to running ssh instance and look what's going on. Maybe we'd have to
probe for at least 1 byte here. Or maybe use some totally different
approach to detect if peer's end of pipe is closed.

I vaguely remember some problems with PeekNamedPipe from times when i
patched tty stuff, but they were somewhat different.

LP> I'm not very familiar with pipes on windows, so I'd appreciate help on this 
LP> subject.

Egor.            mailto:deo AT logos-m DOT ru ICQ 5165414 FidoNet 2:5020/496.19


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