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Date: Mon, 17 Feb 2025 18:00:44 +0100
To: cygwin AT cygwin DOT com
Subject: Re: [CALL FOR TESTING] Cygwin-3.6.0
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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Hi Rainer,

On Feb 17 12:51, Rainer Emrich via Cygwin wrote:
> Hi Corinna,
> 
> Am 14.02.2025 um 20:03 schrieb Corinna Vinschen via Cygwin-announce:
> > we're planning the next major release in the next few (hopefully
> > not more than two) weeks.
> > [...]
> > At this point, we're most interested if the test release introduces
> > regressions compared to 3.5.7!
> > [...]
> 
> I'm facing a strange major issue with scp. The issue exists in all cygwin version later than 3.5.3,
> including cygwin-3.6.0-0.374.g4dd859d01c22.
> 
> If I'm copying a large file with scp I get a "connection lost" after a random couple of seconds:
> 
> scp -v large_file foobar:
> .
> .
> debug1: Sending subsystem: sftp
> debug1: pledge: fork
> large_file                                             10%   71MB   4.3MB/s   02:21 ETA
> debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
> debug1: client_input_channel_req: channel 0 rtype eow AT openssh DOT com reply 0
> debug1: channel 0: free: client-session, nchannels 1
> Transferred: sent 92266460, received 35436 bytes, in 15.3 seconds
> Bytes per second: sent 6035219.0, received 2317.9
> debug1: Exit status 11
> lost connection

In fact, I can reproduce this occassionally back to 3.5.0 and back to
OpenSSH 9.7p1.  We can't easily try this with older Cygwin versions.
It's getting increasingly hard to build older Cygwin versions due to
compiler dependencies and missing symbols.

What that means in the first place, is that this is neither a regression
from 3.5.7, nor even from 3.5.1.  Obviously I can't prove if this has
been introduced into 3.5.0, but I'd like to point out that we didn't
have any noticable change in the socket code for almost 4 years, back
during 3.3 development.

Fun fact: I can NOT reproduce the problem when using the -O option,
i. e., when using the old scp protocol.  The old protocol isn't
slower either.

Maybe that's a workaround for you?

> The strange thing, if I use strace to debug this, the cpoy succeeds:
> strace -efno strace.log scp -v large_file foobar:

This often points to a timing issue, but beats me where that could be.

> I would try to debug this further, if I had an idea how to do that.

Same here ATM, sorry.


Corinna

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