freebsd-src/bin/dd/ref.obs_zeroes

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Reorganize the handling all-zeroes terminal block in sparse mode The intent of the previous code in that case was to force an explicit write, but the implementation was incorrect, and as a result the write was never performed. This new implementation instead uses ftruncate(2) to extend the file with a trailing hole. Also introduce regression tests for these cases. PR: 189284 (original PR whose fix introduced this bug) PR: 207092 Differential Revision: D5248 Reviewed by: sobomax,kib MFC after: 2 weeks 2016-02-18 08:44:16 +00:00			`00000000 41 42 43 44 45 46 47 48 00 00 00 00 00 00 00 00 \|ABCDEFGH........\|`
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