borgbackup test fail on cygwin (only) - cygwin pipe issues?

borgbackup test fail on cygwin (only) - cygwin pipe issues?

[Thomas Waldmann]

Hi,

borgbackup uses a RPC protocol via a ssh pipe to implement client/server
communication.

borg client --pipe-- ssh --tcp-- sshd --pipe-- borg serve

This works very reliable, we have tests running on linux, freebsd,
netbsd, openbsd, OS X. It even works on win10 linux subsystem.

But on Cygwin, only the local tests work, but the remote tests (which
need the pictured ssh pipe) fail or hang.

When trying to find out what's going wrong, I noticed corrupted data
coming over the pipe.

I've found some other pipe issues on the cygwin mailing list, maybe this
is related?

Our issue about this:

https://github.com/borgbackup/borg/issues/1268

Note:

I am one of the borgbackup developers, but I am not a windows developer
(and I personally don't use windows or cygwin except for testing
borgbackup on this platform).

What I could offer is to run the tests on a fixed version.

Thanks for looking into this,

Thomas

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Re: borgbackup test fail on cygwin (only) - cygwin pipe issues?

[cyg Simple]

On 1/10/2017 10:47 PM, Thomas Waldmann wrote:
> Hi,
> 
> borgbackup uses a RPC protocol via a ssh pipe to implement client/server
> communication.
> 
> borg client --pipe-- ssh --tcp-- sshd --pipe-- borg serve
> 
> This works very reliable, we have tests running on linux, freebsd,
> netbsd, openbsd, OS X. It even works on win10 linux subsystem.
> 
> But on Cygwin, only the local tests work, but the remote tests (which
> need the pictured ssh pipe) fail or hang.
> 
> When trying to find out what's going wrong, I noticed corrupted data
> coming over the pipe.
> 
> I've found some other pipe issues on the cygwin mailing list, maybe this
> is related?
> 
> Our issue about this:
> 
> https://github.com/borgbackup/borg/issues/1268
> 

Are your pipe handles in open in binary mode or text mode?  You should
always ensure they are in binary mode.

-- 
cyg Simple

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Re: borgbackup test fail on cygwin (only) - cygwin pipe issues?

[Thomas Waldmann]

>> https://github.com/borgbackup/borg/issues/1268
> 
> Are your pipe handles in open in binary mode or text mode?  You should
> always ensure they are in binary mode.

That was my first idea also.

https://github.com/borgbackup/borg/blob/1.0.9/borg/remote.py#L188 this
is the place where the ssh subprocess is forked and the pipes are set up.

There is nothing special about binary mode there, but as mentioned in
that ticket, I just tried it out to send binary data over such pipes and
it worked:

https://github.com/borgbackup/borg/issues/1268#issuecomment-239923192

(that \n should get modified to \r\n if in text mode, but it got through
"as is")


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Re: borgbackup test fail on cygwin (only) - cygwin pipe issues?

[Thomas Waldmann]

It was a bug in our code that was triggered frequently by the small
cygwin pipe buffer size of only 64kiB.

borgbackup fix/workaround see there:

https://github.com/borgbackup/borg/pull/2032

It (almost?) never happened on other OSes, due to their bigger buffers.

Note:

It would be nice to have bigger pipe buffers on cygwin, for performance
reasons.


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Re: borgbackup test fail on cygwin (only) - cygwin pipe issues?

[Thomas Waldmann]

On 01/13/2017 07:18 PM, Thomas Waldmann wrote:
> It was a bug in our code that was triggered frequently by the small
> cygwin pipe buffer size of only 64kiB.
> 
> borgbackup fix/workaround see there:
> 
> https://github.com/borgbackup/borg/pull/2032
> 
> It (almost?) never happened on other OSes, due to their bigger buffers.

Hmm, the last phrase seems not to be the real reason why it worked
there, but rather that neither Linux nor *BSD ever do partial writes on
blocking pipes.

So, should cygwin also behave that ^^^ way on blocking pipes?


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Re: borgbackup test fail on cygwin (only) - cygwin pipe issues?

[Corinna Vinschen]

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On Jan 13 20:07, Thomas Waldmann wrote:
> On 01/13/2017 07:18 PM, Thomas Waldmann wrote:
> > It was a bug in our code that was triggered frequently by the small
> > cygwin pipe buffer size of only 64kiB.
> > 
> > borgbackup fix/workaround see there:
> > 
> > https://github.com/borgbackup/borg/pull/2032
> > 
> > It (almost?) never happened on other OSes, due to their bigger buffers.
> 
> Hmm, the last phrase seems not to be the real reason why it worked
> there, but rather that neither Linux nor *BSD ever do partial writes on
> blocking pipes.
> 
> So, should cygwin also behave that ^^^ way on blocking pipes?

Yes.  I inspected the code and the current behaviout was apparently
an accident when refactoring the pipe write code.  I applied a patch
and uploaded new developer snapshots to https://cygwin.com/snapshots/
Please give them a try.


Thanks,
Corinna

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Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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