Function space_map_iterate

freebsd/contrib/openzfs/module/zfs/space_map.c:85–191

* Iterate through the space map, invoking the callback on each (non-debug) * space map entry. Stop after reading 'end' bytes of the space map. */

 * space map entry. Stop after reading 'end' bytes of the space map.
 */
int
space_map_iterate(space_map_t *sm, uint64_t end, sm_cb_t callback, void *arg)
{
	uint64_t blksz = sm->sm_blksz;

	ASSERT3U(blksz, !=, 0);
	ASSERT3U(end, <=, space_map_length(sm));
	ASSERT0(P2PHASE(end, sizeof (uint64_t)));

	dmu_prefetch(sm->sm_os, space_map_object(sm), 0, 0, end,
	    ZIO_PRIORITY_SYNC_READ);

	int error = 0;
	uint64_t txg = 0, sync_pass = 0;
	for (uint64_t block_base = 0; block_base < end && error == 0;
	    block_base += blksz) {
		dmu_buf_t *db;
		error = dmu_buf_hold(sm->sm_os, space_map_object(sm),
		    block_base, FTAG, &db, DMU_READ_PREFETCH);
		if (error != 0)
			return (error);

		uint64_t *block_start = db->db_data;
		uint64_t block_length = MIN(end - block_base, blksz);
		uint64_t *block_end = block_start +
		    (block_length / sizeof (uint64_t));

		VERIFY0(P2PHASE(block_length, sizeof (uint64_t)));
		VERIFY3U(block_length, !=, 0);
		ASSERT3U(blksz, ==, db->db_size);

		for (uint64_t *block_cursor = block_start;
		    block_cursor < block_end && error == 0; block_cursor++) {
			uint64_t e = *block_cursor;

			if (sm_entry_is_debug(e)) {
				/*
				 * Debug entries are only needed to record the
				 * current TXG and sync pass if available.
				 *
				 * Note though that sometimes there can be
				 * debug entries that are used as padding
				 * at the end of space map blocks in-order
				 * to not split a double-word entry in the
				 * middle between two blocks. These entries
				 * have their TXG field set to 0 and we
				 * skip them without recording the TXG.
				 * [see comment in space_map_write_seg()]
				 */
				uint64_t e_txg = SM_DEBUG_TXG_DECODE(e);
				if (e_txg != 0) {
					txg = e_txg;
					sync_pass = SM_DEBUG_SYNCPASS_DECODE(e);
				} else {
					ASSERT0(SM_DEBUG_SYNCPASS_DECODE(e));
				}
				continue;
			}