This extension defines a facility for plugins to get information about the block length (the sample_count parameter of LV2_Descriptor::run) and port buffer sizes, as well as several features which can be used to restrict the block length.
This extension defines features and properties but has no special purpose API of its own. The host provides all the relevant information to the plugin as options.
To require restrictions on the block length, plugins can require additional features: bufsz:boundedBlockLength, bufsz:powerOf2BlockLength, and bufsz:fixedBlockLength. These features are data-only, that is they merely indicate a restriction and do not carry any data or API.