find_zero_byte_in_word(9)

💖 NAME 💖

hey bestie, welcome to find_zero_byte_in_word(9) from the Kernel API Manual — this one is literally about finding the array index of the first zero byte in a word-sized range of reference counters. lowkey iconic 💅

✨ SYNOPSIS ✨

slab_block_number find_zero_byte_in_word (const u8 *word_ptr ,
slab_block_number start_index , slab_block_number fail_index );

🎀 ARGUMENTS 🎀

• word_ptr — a pointer to the eight counter bytes to check, periodt.
• start_index — the array index that corresponds to word_ptr[0].
• fail_index — the array index to return if no zero byte is found. your fallback bestie 🫶

🦋 DESCRIPTION 🦋

okay so real talk: the search does no bounds checking. none. zero. the function relies on the array being sufficiently padded — that's the whole safety situation, bestie 🚨

🌸 RETURN 🌸

it returns the array index of the first zero byte in the word, or the value passed as fail_index if no zero byte was found. that's it, that's the return 💖

🔥 SEE ALSO 🔥

Kernel file ./drivers/md/dm-vdo/slab-depot.c is the home base for all this. the whole squad is:

• get_lock(9), must_make_entries_to_flush(9), is_reaping(9), initialize_tail_block(9)
• initialize_journal_state(9), block_is_full(9), is_slab_journal_blank(9), mark_slab_journal_dirty(9), compute_fullness_hint(9)
• check_summary_drain_complete(9), notify_summary_waiters(9), finish_updating_slab_summary_block(9), finish_update(9), handle_write_error(9), launch_write(9), update_slab_summary_entry(9)
• finish_reaping(9), complete_reaping(9), handle_flush_error(9), flush_for_reaping(9), reap_slab_journal(9), adjust_slab_journal_block_reference(9), release_journal_locks(9)
• update_tail_block_location(9), reopen_slab_journal(9), complete_write(9), write_slab_journal_block(9), commit_tail(9), encode_slab_journal_entry(9), expand_journal_point(9), add_entry(9)
• vdo_attempt_replay_into_slab(9), requires_reaping(9), launch_reference_block_write(9), finish_reference_block_write(9), get_reference_counters_for_block(9), pack_reference_block(9), handle_io_error(9), write_reference_block(9)
• reference_count_to_status(9), dirty_block(9), get_reference_block(9), slab_block_number_from_pbn(9), get_reference_counter(9), adjust_free_block_count(9), increment_for_data(9), decrement_for_data(9), increment_for_block_map(9)
• update_reference_count(9), add_entry_from_waiter(9), is_next_entry_a_block_map_increment(9), add_entries(9), reset_search_cursor(9), advance_search_cursor(9)
• vdo_adjust_reference_count_for_rebuild(9), replay_reference_count_change(9), find_free_block(9), search_current_reference_block(9), search_reference_blocks(9), make_provisional_reference(9), dirty_all_reference_blocks(9)
• match_bytes(9), count_valid_references(9), unpack_reference_block(9), finish_reference_block_load(9), load_reference_block_group(9), load_reference_blocks(9)
• drain_slab(9), read_slab_journal_tail(9), load_slab_journal(9), get_next_slab(9), has_slabs_to_scrub(9), uninitialize_scrubber_vio(9), finish_scrubbing(9), slab_scrubbed(9), abort_scrubbing(9), handle_scrubber_error(9), apply_block_entries(9), apply_journal_entries(9), start_scrubbing(9), scrub_next_slab(9), scrub_slabs(9), get_depot_slab_iterator(9), next_slab(9)
• abort_waiter(9), vdo_acquire_provisional_reference(9), open_slab(9), vdo_enqueue_clean_slab_waiter(9), vdo_modify_reference_count(9), vdo_notify_slab_journals_are_recovered(9), make_slab(9), allocate_slabs(9), vdo_abandon_new_slabs(9)
• release_recovery_journal_lock(9), prepare_for_tail_block_commit(9), schedule_tail_block_commit(9), initialize_slab_scrubber(9), initialize_slab_summary_block(9), vdo_decode_slab_depot(9), vdo_free_slab_depot(9), vdo_record_slab_depot(9), vdo_allocate_reference_counters(9), get_slab_number(9), vdo_get_slab(9), vdo_get_increment_limit(9), vdo_is_physical_data_block(9), vdo_get_slab_depot_allocated_blocks(9), vdo_get_slab_depot_data_blocks(9)
• finish_combining_zones(9), combine_summaries(9), finish_loading_summary(9), load_slab_summary(9), vdo_load_slab_depot(9), vdo_prepare_slab_depot_to_allocate(9), vdo_update_slab_depot_size(9), vdo_prepare_to_grow_slab_depot(9)
• finish_registration(9), vdo_use_new_slabs(9), stop_scrubbing(9), vdo_drain_slab_depot(9), resume_scrubbing(9), vdo_resume_slab_depot(9), vdo_commit_oldest_slab_journal_tail_blocks(9), vdo_scrub_all_unrecovered_slabs(9)
• get_block_allocator_statistics(9), get_ref_counts_statistics(9), get_slab_journal_statistics(9), vdo_get_slab_depot_statistics(9), vdo_dump_slab_depot(9)

💌 okay that's the page! this one is from ./drivers/md/dm-vdo, dated October 2026, and it's chillin' in the Kernel API Manual as find_zero_byte_in_word(9). mwah 💋