Re: dd: reblock failure -- sporadic failures

[Jim Meyering]

Pádraig Brady <address@hidden> wrote:
> Jim Meyering wrote:
>> diff --git a/tests/dd/reblock b/tests/dd/reblock
>> index 542529a..ef9e036 100755
>> --- a/tests/dd/reblock
>> +++ b/tests/dd/reblock
>> @@ -44,7 +44,10 @@ sed 's/,.*//' err > k && mv k err
>>  compare err exp-reblock || fail=1
>>
>>  # Demonstrate that bs=N supersedes even following ibs= and obs= settings.
>> -(echo x; sleep .1; echo y) | dd bs=3 ibs=1 obs=1 > out 2> err || fail=1
>> +# Choosing a delay of 0.1 would result in an occasional lost race where
>> +# the consumer's first read would consume 3 bytes rather than the expected 
>> 2.
>> +# Not wanting to sleep a full second, I'll raise that to 0.3.
>> +(printf ab; sleep .3; printf cd) | dd bs=3 ibs=1 obs=1 > out 2> err || 
>> fail=1
>>  sed 's/,.*//' err > k && mv k err
>>  compare err exp-no-reblock || fail=1
>
> Doesn't the same logic need to be applied to both tests in this file,
> as they both expect 2 short reads?

Yes.  Good point.

> Hmm, I wonder is there a way to get the producer
> to wait until the consumer is ready.
> I think both open()s on a fifo block on each other,
> so the following would cause `printf ab` to happen
> after dd has executed open(), which might help?
>
> mkfifo dd.fifo
> dd ibs=3 obs=3 if=dd.fifo > out 2> err&
> (printf ab; sleep .1; printf cd) > dd.fifo
> wait #for dd to complete
> sed 's/,.*//' err > k && mv k err
> compare err exp-no-reblock || fail=1

Good idea.
That looks like a more reliable solution.
Do you feel like writing the patch?