Rocksdb can not ingest .SST under linux with readonly prermissions (0444)

[socketpair]

RocksDB: Ingesting diff FAILED: IO error: While open a file for appending: /var/cache/ideco/content-filter-backend/db_v2/000366.sst: Permission denied

While doing atandard ingesting function
i.e. after moving (rename()) original .sst file into DB directory it tries to open() it with O_APPEND and fails. Yes, it, does not change the file (does not write). but opens with ability to append. for unknown reason. I consider it a bug.

IngestExternalFileOptions ifo;
    ifo.failed_move_fall_back_to_copy = false;
    ifo.move_files = true;
    ifo.verify_checksums_before_ingest = false; // as default
    ifo.verify_file_checksum = false; // speedup
    ifo.write_global_seqno = false; // we are the new project.
db->IngestExternalFile({ sst_file }, ifo);

rocksdb-9.3.1-2.fc41.x86_64