Date: Fri, 10 Feb 2012 20:50:12 GMT From: Diomidis Spinellis <dds@aueb.gr> To: freebsd-bugs@FreeBSD.org Subject: Re: bin/164947: tee looses data when writing to non-blocking file descriptors Message-ID: <201202102050.q1AKoCe6064490@freefall.freebsd.org>
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The following reply was made to PR bin/164947; it has been noted by GNATS. From: Diomidis Spinellis <dds@aueb.gr> To: Martin Cracauer <cracauer@cons.org> Cc: freebsd-gnats-submit@freebsd.org Subject: Re: bin/164947: tee looses data when writing to non-blocking file descriptors 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 [...] >>> How-To-Repeat: >> Run the following: >> #!/usr/local/bin/bash >> # 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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