bin/164947: tee looses data when writing to non-blocking file
dds at aueb.gr
Fri Feb 10 20:50:12 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 22:32:02 +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.
> That doesn't mean I am opposed to handling EAGAIN.
> The way I normally do it is a simple retry loop, not using select.
> I'm aware of the tradeoffs, so far I was always better off not
> investing a second system call into every retry.
I agree this can be cheaper for many cases, but it can become very
expensive for long waits.
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