Re: [PATCH v8] read-cache: call verify_hdr() in a background thread

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

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

> git@jeffhostetler.com writes:
>
>> From: Jeff Hostetler <jeffhost@microsoft.com>
>>
>> Version 8 of this patch converts the unit test to use
>> perl to corrupt the index checksum (rather than altering
>> a filename) and also verifies the fsck error message as
>> suggested in response to v7 on the mailing list.
>>
>> If there are no other suggestions, I think this version
>> should be considered final.
>
> Oops.  The earlier one has already been in 'master' for a few days.
> Let's make this an incremental update.  
>
> Is the description in the following something you are OK with (so
> that I can add your sign-off)?
>
> Thanks.

By the way, I said I am fine with the two-liner version in Dscho's
message, but I am also OK with this version that does not use a
separate dd and instead does everything in a single invocation of
Perl.  As long as you've tested this version, there is no point
replacing it with yet another one.

Thanks.

> -- >8 --
> From: Jeff Hostetler <jeffhost@microsoft.com>
> Date: Tue, 25 Apr 2017 18:41:09 +0000
> Subject: t1450: avoid use of "sed" on the index, which is a binary file
>
> The previous step added a path zzzzzzzz to the index, and then used
> "sed" to replace this string to yyyyyyyy to create a test case where
> the checksum at the end of the file does not match the contents.
>
> Unfortunately, use of "sed" on a non-text file is not portable.
> Instead, use a Perl script that seeks to the end and modifies the
> last byte of the file (where we _know_ stores the trailing
> checksum).
>
>
> ---
>  t/t1450-fsck.sh | 33 ++++++++++++++++++++++++++-------
>  1 file changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
> index 677e15a7a4..eff1cd68e9 100755
> --- a/t/t1450-fsck.sh
> +++ b/t/t1450-fsck.sh
> @@ -689,16 +689,35 @@ test_expect_success 'bogus head does not fallback to all heads' '
>  	! grep $blob out
>  '
>  
> +# Corrupt the checksum on the index.
> +# Add 1 to the last byte in the SHA.
> +corrupt_index_checksum () {
> +    perl -w -e '
> +	use Fcntl ":seek";
> +	open my $fh, "+<", ".git/index" or die "open: $!";
> +	binmode $fh;
> +	seek $fh, -1, SEEK_END or die "seek: $!";
> +	read $fh, my $in_byte, 1 or die "read: $!";
> +
> +	$in_value = unpack("C", $in_byte);
> +	$out_value = ($in_value + 1) & 255;
> +
> +	$out_byte = pack("C", $out_value);
> +
> +	seek $fh, -1, SEEK_END or die "seek: $!";
> +	print $fh $out_byte;
> +	close $fh or die "close: $!";
> +    '
> +}
> +
> +# Corrupt the checksum on the index and then
> +# verify that only fsck notices.
>  test_expect_success 'detect corrupt index file in fsck' '
>  	cp .git/index .git/index.backup &&
>  	test_when_finished "mv .git/index.backup .git/index" &&
> -	echo zzzzzzzz >zzzzzzzz &&
> -	git add zzzzzzzz &&
> -	sed -e "s/zzzzzzzz/yyyyyyyy/" .git/index >.git/index.yyy &&
> -	mv .git/index.yyy .git/index &&
> -	# Confirm that fsck detects invalid checksum
> -	test_must_fail git fsck --cache &&
> -	# Confirm that status no longer complains about invalid checksum
> +	corrupt_index_checksum &&
> +	test_must_fail git fsck --cache 2>expect &&
> +	grep "bad index file" expect &&
>  	git status
>  '
>