bin/164947: tee looses data when writing to non-blocking file
dds at aueb.gr
Fri Feb 10 21:20:12 UTC 2012
The following reply was made to PR bin/164947; it has been noted by GNATS.
From: Diomidis Spinellis <dds at aueb.gr>
To: Martin Cracauer <cracauer at cons.org>
Cc: freebsd-gnats-submit at freebsd.org
Subject: Re: bin/164947: tee looses data when writing to non-blocking file
Date: Fri, 10 Feb 2012 23:17:03 +0200
On 10/02/2012 23:03, Martin Cracauer wrote:
> Diomidis Spinellis wrote on Fri, Feb 10, 2012 at 10:32:02PM +0200:
>> On 10/02/2012 21:17, Martin Cracauer wrote:
>>> Diomidis Spinellis wrote on Fri, Feb 10, 2012 at 07:04:41AM +0000:
>>>>> Number: 164947
>>>> Run the following:
>>>> # bash needed for the>(...) functionality
>>>> # ssh apparently sets O_NONBLOCK
>>>> # Remove the 2>/dev/null to see tee complaining
>>>> dd count=100000 if=/dev/zero |
>>>> tee>(ssh localhost dd of=/dev/null) 2>/dev/null |
>>>> (ssh localhost dd of=/dev/null)
>>> I don't think it is ssh that is causing this. If you use a named pipe
>>> explicitly and hook ssh up to that the error doesn't appear. Seems to
>>> be something that bash is doing there.
>> I think the named pipe isolates the write fd from the ssh end. If you
>> use cat or dd instead of ssh the problem goes away.
> Do you happen to know what bash does there, exactly? I was assuming it
> is creating a named pipe behind the user's back.
It is creating a normal pipe and providing it as an argument through
ls -l /dev/fd >(wc -l)
> I noticed that if you do ssh on the "tee part" and something else on
> the end of the regular pipe then things also fail. On the other hand
> if you put the "tee part" on something else and the regular pipe on
> ssh things never seem to fail.
On 8.1 release I needed both ends to run ssh to see the problem.
BTW The problem also manifests itself on Mac OS X and Linux :-)
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