Re: [PATCH v3 15/24] midx: write object offsets

> On Thu, Jul 5, 2018 at 8:54 PM Derrick Stolee <stolee@gmail.com> wrote:
>> The final pair of chunks for the multi-pack-index file stores the object
>> offsets. We default to using 32-bit offsets as in the pack-index version
>> 1 format, but if there exists an offset larger than 32-bits, we use a
>> trick similar to the pack-index version 2 format by storing all offsets
>> at least 2^31 in a 64-bit table; we use the 32-bit table to point into
>> that 64-bit table as necessary.
>>
>> We only store these 64-bit offsets if necessary, so create a test that
>> manipulates a version 2 pack-index to fake a large offset. This allows
>> us to test that the large offset table is created, but the data does not
>> match the actual packfile offsets. The multi-pack-index offset does match
>> the (corrupted) pack-index offset, so a future feature will compare these
>> offsets during a 'verify' step.
>>
>> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
>> ---
>> diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
>> @@ -6,25 +6,28 @@ test_description='multi-pack-indexes'
>> +# usage: corrupt_data <file> <pos> [<data>]
>> +corrupt_data() {
> Style: corrupt_data () {
>
>> +       file=$1
>> +       pos=$2
>> +       data="${3:-\0}"
>> +       printf "$data" | dd of="$file" bs=1 seek="$pos" conv=notrunc
>> +}
>> +
>> +# Force 64-bit offsets by manipulating the idx file.
>> +# This makes the IDX file _incorrect_ so be careful to clean up after!
>> +test_expect_success 'force some 64-bit offsets with pack-objects' '
>> +       mkdir objects64 &&
>> +       mkdir objects64/pack &&
>> +       pack64=$(git pack-objects --index-version=2,0x40 objects64/pack/test-64 <obj-list) &&
>> +       idx64=objects64/pack/test-64-$pack64.idx &&
>> +       chmod u+w $idx64 &&
> I guess you don't have to worry about the POSIXPERM prerequisite here
> because the file is already writable on Windows, right?