Function dbuf_assign_arcbuf

freebsd/contrib/openzfs/module/zfs/dbuf.c:2661–2725

* Directly assign a provided arc buf to a given dbuf if it's not referenced * by anybody except our caller. Otherwise copy arcbuf's contents to dbuf. */

 * by anybody except our caller. Otherwise copy arcbuf's contents to dbuf.
 */
void
dbuf_assign_arcbuf(dmu_buf_impl_t *db, arc_buf_t *buf, dmu_tx_t *tx)
{
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));
	ASSERT(db->db_blkid != DMU_BONUS_BLKID);
	ASSERT(db->db_level == 0);
	ASSERT3U(dbuf_is_metadata(db), ==, arc_is_metadata(buf));
	ASSERT(buf != NULL);
	ASSERT3U(arc_buf_lsize(buf), ==, db->db.db_size);
	ASSERT(tx->tx_txg != 0);

	arc_return_buf(buf, db);
	ASSERT(arc_released(buf));

	mutex_enter(&db->db_mtx);

	while (db->db_state == DB_READ || db->db_state == DB_FILL)
		cv_wait(&db->db_changed, &db->db_mtx);

	ASSERT(db->db_state == DB_CACHED || db->db_state == DB_UNCACHED);

	if (db->db_state == DB_CACHED &&
	    zfs_refcount_count(&db->db_holds) - 1 > db->db_dirtycnt) {
		/*
		 * In practice, we will never have a case where we have an
		 * encrypted arc buffer while additional holds exist on the
		 * dbuf. We don't handle this here so we simply assert that
		 * fact instead.
		 */
		ASSERT(!arc_is_encrypted(buf));
		mutex_exit(&db->db_mtx);
		(void) dbuf_dirty(db, tx);
		bcopy(buf->b_data, db->db.db_data, db->db.db_size);
		arc_buf_destroy(buf, db);
		return;
	}

	if (db->db_state == DB_CACHED) {
		dbuf_dirty_record_t *dr = list_head(&db->db_dirty_records);

		ASSERT(db->db_buf != NULL);
		if (dr != NULL && dr->dr_txg == tx->tx_txg) {
			ASSERT(dr->dt.dl.dr_data == db->db_buf);

			if (!arc_released(db->db_buf)) {
				ASSERT(dr->dt.dl.dr_override_state ==
				    DR_OVERRIDDEN);
				arc_release(db->db_buf, db);
			}
			dr->dt.dl.dr_data = buf;
			arc_buf_destroy(db->db_buf, db);
		} else if (dr == NULL || dr->dt.dl.dr_data != db->db_buf) {
			arc_release(db->db_buf, db);
			arc_buf_destroy(db->db_buf, db);
		}
		db->db_buf = NULL;
	}
	ASSERT(db->db_buf == NULL);