Re: [Patch v1 2/3] t5318: replace use of /dev/zero with generate_zero_bytes

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

> Eric Sunshine <sunshine@sunshineco.com> writes:
>
>> On Sat, Feb 9, 2019 at 2:00 PM <randall.s.becker@rogers.com> wrote:
>>> This change removes the dependency on /dev/zero with generate_zero_bytes
>>> appending NUL values to blocks generating wrong signatures for test cases.
>>
>> This commit message says what the patch does but not _why_. At
>> minimum, it should explain that /dev/zero is not available on all
>> platforms, therefore, not portable, and (perhaps) cite NonStop as an
>> example.
>
> Does sombody want to do the honors?  [PATCH 1/3] would become wasted
> effort until that happens.  On the other hand, if this is not urgent
> (it is only urgent for those without /dev/zero, and to others it may
> be distraction/disruption this close to the final release to add
> increased risk of fat finger mistakes), obviously I can wait.

So, before I lose the access to my primary screen (I was told that
somehow I need to reimage the workstation today X-<), here is what I
have now.

-- >8 --
From: "Randall S. Becker" <rsbecker@nexbridge.com>
Date: Sat, 9 Feb 2019 13:59:29 -0500
Subject: [PATCH] t5318: replace use of /dev/zero with generate_zero_bytes

There are platforms (e.g. NonStop) that lack /dev/zero; use the
generate_zero_bytes helper we just introduced to append stream
of NULs at the end of the file.

The original, even though it uses "dd seek=... count=..." to make it
look like it is overwriting the middle part of an existing file, has
truncated the file before this step with another use of "dd", which
may make it tricky to see why this rewrite is a correct one.

Signed-off-by: Randall S. Becker <rsbecker@nexbridge.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t5318-commit-graph.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 16d10ebce8..d4bd1522fe 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -383,7 +383,7 @@ corrupt_graph_and_verify() {
 	cp $objdir/info/commit-graph commit-graph-backup &&
 	printf "$data" | dd of="$objdir/info/commit-graph" bs=1 seek="$pos" conv=notrunc &&
 	dd of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=0 &&
-	dd if=/dev/zero of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=$(($orig_size - $zero_pos)) &&
+	generate_zero_bytes $(($orig_size - $zero_pos)) >>"$objdir/info/commit-graph" &&
 	test_must_fail git commit-graph verify 2>test_err &&
 	grep -v "^+" test_err >err &&
 	test_i18ngrep "$grepstr" err
-- 
2.21.0-rc0-36-ge9bd4aa026