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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri, 4 Jan 2019 13:59:16 +0100
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Subject: Re: [Qemu-devel] [PULL v4 00/35] Misc patches for 2018-12-21
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>

On 04/01/19 12:31, Peter Maydell wrote:
> I'll give this a go, but I think this will not necessarily be
> sufficient if some program invoked by make sets the O_NONBLOCK flag,
> and then make later in the same run tries to output and gets EINTR.
> Perhaps it would be better to put it in the test harness that
> invokes test binaries, so as to clear the flag as soon
> as possible? It could also then in theory print a warning
> if a test case had put stdin/stdout into non-blocking mode.

Aha, you gave me the clue I needed. :)  gtester redirected stdin/out/err
to /dev/null.

In the new harness, stdout is piped into tap-driver.pl, but everything
else is left in place.  Leaving stderr should be safe, while stdin is
the most likely culprit.  Adding </dev/null to the test invocation
should fix it; I'll send a new pull request either today or next Monday.

> (The semantics of O_NONBLOCK here seem to me to be completely
> broken. But they are what they are...)

Yes, and F_SETFL is not the only "interesting" fcntl in this respect;
fortunately QEMU is not using F_SETOWN anymore!

Paolo