reftable: write correct max_update_index to header In 297c09eabb (refs: allow multiple reflog entries for the same refname, 2024-12-16), the reftable backend learned to handle multiple reflog entries within the same transaction. This was done modifying the `update_index` for reflogs with multiple indices. During writing the logs, the `max_update_index` of the writer was modified to ensure the limits were raised to the modified `update_index`s. However, since ref entries are written before the modification to the `max_update_index`, if there are multiple blocks to be written, the reftable backend writes the header with the old `max_update_index`. When all logs are finally written, the footer will be written with the new `min_update_index`. This causes a mismatch between the header and the footer and causes the reftable file to be corrupted. The existing tests only spawn a single block and since headers are lazily written with the first block, the tests didn't capture this bug. To fix the issue, the appropriate `max_update_index` limit must be set even before the first block is written. Add a `max_index` field to the transaction which holds the `max_index` within all its updates, then propagate this value to the reftable backend, wherein this is used to the set the `max_update_index` correctly. Add a test which creates a few thousand reference updates with multiple reflog entries, which should trigger the bug. Reported-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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