Filecoin Proving Subsystem

The Filecoin Proving Subsystem (or FPS) provides the storage proofs required by the Filecoin protocol. It is implemented entirely in Rust, as a series of partially inter-dependent crates – some of which export C bindings to the supported API.

There are currently several different crates:

• Storage Proofs (storage-proofs) A library for constructing storage proofs – including non-circuit proofs, corresponding SNARK circuits, and a method of combining them.

• Storage Proofs Core (storage-proofs-core) A set of common primitives used throughout the other storage-proofs sub-crates, including crypto, merkle tree, hashing and gadget interfaces.

• Storage Proofs PoRep (storage-proofs-porep) storage-proofs-porep is intended to serve as a reference implementation for Proof-of-Replication (PoRep), while also performing the heavy lifting for filecoin-proofs.

  Primary Components:

  • PoR (Proof-of-Retrievability: Merkle inclusion proof)
  • DrgPoRep (Depth Robust Graph Proof-of-Replication)
  • StackedDrgPoRep

• Storage Proofs PoSt (storage-proofs-post) storage-proofs-post is intended to serve as a reference implementation for Proof-of-Space-time (PoSt), for filecoin-proofs.

  Primary Components:

  • PoSt (Proof-of-Spacetime)

• Filecoin Proofs (filecoin-proofs) A wrapper around storage-proofs, providing an FFI-exported API callable from C (and in practice called by lotus via cgo). Filecoin-specific values of setup parameters are included here.

Security Audits

rust-fil-proofs has undergone a SNARK proofs security audit performed by Dr. Jean-Philippe Aumasson and Antony Vennard and been deemed free of critical or major security issues. In addition to the security analysis, the document provides the audit goals, methodology, functionality descriptions and finally observations on what could be improved. All known issues have been resolved to date.

Design Notes

Earlier in the design process, we considered implementing what has become the FPS in Go – as a wrapper around potentially multiple SNARK circuit libraries. We eventually decided to use bellman – a library developed by Zcash, which supports efficient pedersen hashing inside of SNARKs. Having made that decision, it was natural and efficient to implement the entire subsystem in Rust. We considered the benefits (self-contained codebase, ability to rely on static typing across layers) and costs (developer ramp-up, sometimes unwieldiness of borrow-checker) as part of that larger decision and determined that the overall project benefits (in particular ability to build on Zcash’s work) outweighed the costs.

We also considered whether the FPS should be implemented as a standalone binary accessed from Filecoin nodes either as a single-invocation CLI or as a long-running daemon process. Bundling the FPS as an FFI dependency was chosen for both the simplicity of having a Filecoin node deliverable as a single monolithic binary, and for the (perceived) relative development simplicity of the API implementation.

If at any point it were to become clear that the FFI approach is irredeemably problematic, the option of moving to a standalone FPS remains. However, the majority of technical problems associated with calling from Go into Rust are now solved, even while allowing for a high degree of runtime configurability. Therefore, continuing down the same path we have already invested in, and have begun to reap rewards from, seems likely.

Install and configure Rust

NOTE: If you have installed rust-fil-proofs incidentally, as a submodule of lotus, then you may already have installed Rust.

The instructions below assume you have independently installed rust-fil-proofs in order to test, develop, or experiment with it.

Install Rust using rustup.

Build

NOTE: rust-fil-proofs can only be built for and run on 64-bit platforms; building will panic if the target architecture is not 64-bits.

Before building you will need OpenCL to be installed, on Ubuntu this can be achieved with apt install ocl-icd-opencl-dev. Other system dependencies such as 'gcc/clang', 'wall' and 'cmake' are also required.

> cargo build --release --all

Test

> cargo test --all

Benchmarks

The main benchmarking tool is called benchy. benchy has several subcommands, including merkleproofs, prodbench, winning_post and window_post. You can run them with various configuration options, but some examples are below:

> cargo run --release--bin benchy -- merkleproofs --size 2
> cargo run --release--bin benchy -- winning-post --size 2
> cargo run --release--bin benchy -- window-post --size 2
> cargo run --release--bin benchy -- prodbench

There is also a bench called gpu-cpu-test:

> cargo run --release --bin gpu-cpu-test

Some results are displayed at the command line, or alternatively written as JSON files. Logging can be enabled using the RUST_LOG=trace option (see more Logging options in the Logging section below).

Note: On macOS you need gtime (brew install gnu-time), as the built in time command is not enough.

Logging

For better logging with backtraces on errors, developers should use expects rather than expect on Result<T, E> and Option<T>.

The crate use log for logging, which by default does not log at all. In order to log output crates like fil_logger can be used.

For example

fn main() {
    fil_logger::init();
}

and then when running the code setting

> RUST_LOG=filecoin_proofs=info

will enable all logging.

For advanced/verbose/debug logging, you can use the code setting

> RUST_LOG=trace

Settings

Further down in this README, various settings are described that can be adjusted by the end-user. These settings are summarized in rust-fil-proofs.config.toml.sample and this configuration file can be used directly if copied to ./rust-fil-proofs.config.toml. Alternatively, each setting can be set by using environment variables of the form "FIL_PROOFS_", in all caps. For example, to set rows_to_discard to the value 2, you would set FIL_PROOFS_ROWS_TO_DISCARD=2 in your environment.

Any configuration setting that is not specified has a reasonable default already chosen.

To verify current environment settings, you can run:

cargo run --bin settings

Parameter File Location

Filecoin proof parameter files are expected to be located in /var/tmp/filecoin-proof-parameters. If they are located in an alternate location, you can point the system to that location using an environment variable

FIL_PROOFS_PARAMETER_CACHE=/path/to/parameters

Optimizing for either speed or memory during replication

While replicating and generating the Merkle Trees (MT) for the proof at the same time there will always be a time-memory trade-off to consider, we present here strategies to optimize one at the cost of the other.

Speed

One of the most computational expensive operations during replication (besides the encoding itself) is the generation of the indexes of the (expansion) parents in the Stacked graph, implemented through a Feistel cipher (used as a pseudorandom permutation). To reduce that time we provide a caching mechanism to generate them only once and reuse them throughout replication (across the different layers). Already built into the system it can be activated with the environmental variable

FIL_PROOFS_MAXIMIZE_CACHING=1

To check that it's working you can inspect the replication log to find using parents cache of unlimited size. As the log indicates, we don't have a fine grain control at the moment so it either stores all parents or none. This cache will add about 1.5x the entire sector size to the disk cache used during replication, and a configurable sliding window of cached data is used as memory overhead. This setting is very recommended as it has a considerable impact on replication time.

You can also verify if the cache is working by inspecting the time each layer takes to encode, encoding, layer: in the log, where the first two layers, forward and reverse, will take more time than the rest to populate the cache while the remaining 8 should see a considerable time drop.

Note that this setting is enabled by default. It can be disabled by setting the value to 0.

A related setting that can also be tuned is the SDR parents cache size. This value is defaulted to 2048 nodes, which is the equivalent of 112KiB of resident memory (where each cached node consists of DEGREE (base + exp = 6 + 8) x 4 byte elements = 56 bytes in length). Given that the cache is now located on disk, it is memory mapped when accessed in window sizes related to this variable. This default was chosen to minimize memory while still allowing efficient access to the cache. If you would like to experiment with alternate sizes, you can modify the environment variable

FIL_PROOFS_SDR_PARENTS_CACHE_SIZE=2048

Increasing this value will increase the amount of resident RAM used.

Lastly, the parent's cache data is located on disk by default in /var/tmp/filecoin-parents. To modify this location, use the environment variable

FIL_PROOFS_PARENT_CACHE=/path/to/parent/cache

Using the above, the cache data would be located at /path/to/parent/cache/filecoin-parents.

Alternatively, use FIL_PROOFS_CACHE_DIR=/path/to/parent/cache, in which the parent cache will be located in $FIL_PROOFS_CACHE_DIR/filecoin-parents. Note that if you're using FIL_PROOFS_CACHE_DIR, it must be set through the environment and cannot be set using the configuration file. This setting has no effect if FIL_PROOFS_PARENT_CACHE is also specified.

GPU Usage

We can now optionally build the column hashed tree 'tree_c' using the GPU with noticeable speed-up over the CPU. To activate the GPU for this, use the environment variable

FIL_PROOFS_USE_GPU_COLUMN_BUILDER=1

We can optionally also build 'tree_r_last' using the GPU, which provides at least a 2x speed-up over the CPU. To activate the GPU for this, use the environment variable

FIL_PROOFS_USE_GPU_TREE_BUILDER=1

Note that both of these GPU options can and should be enabled if a supported GPU is available.

Advanced GPU Usage

If using the GPU to build tree_c (using FIL_PROOFS_USE_GPU_COLUMN_BUILDER=1), two experimental variables can be tested for local optimization of your hardware. First, you can set

FIL_PROOFS_MAX_GPU_COLUMN_BATCH_SIZE=X

The default value for this is 400,000, which means that we compile 400,000 columns at once and pass them in batches to the GPU. Each column is a "single node x the number of layers" (e.g. a 32GiB sector has 11 layers, so each column consists of 11 nodes). This value is used as both a reasonable default, but it's also measured that it takes about as much time to compile this size batch as it does for the GPU to consume it (using the 2080ti for testing), which we do in parallel for maximized throughput. Changing this value may exhaust GPU RAM if set too large, or may decrease performance if set too low. This setting is made available for your experimentation during this step.

The second variable that may affect performance is the size of the parallel write buffers when storing the tree data returned from the GPU. This value is set to a reasonable default of 262,144, but you may adjust it as needed if an individual performance benefit can be achieved. To adjust this value, use the environment variable

FIL_PROOFS_COLUMN_WRITE_BATCH_SIZE=Y

A similar option for building 'tree_r_last' exists. The default batch size is 700,000 tree nodes. To adjust this, use the environment variable

FIL_PROOFS_MAX_GPU_TREE_BATCH_SIZE=Z

Memory

At the moment the default configuration is set to reduce memory consumption as much as possible so there's not much to do from the user side. We are now storing Merkle trees on disk, which were the main source of memory consumption. You should expect a maximum RSS between 1-2 sector sizes, if you experience peaks beyond that range please report an issue (you can check the max RSS with the /usr/bin/time -v command).

Advanced Storage Tuning

With respect to the 'tree_r_last' cached Merkle Trees persisted on disk, a value is exposed for tuning the amount of storage space required. Cached merkle trees are like normal merkle trees, except we discard some number of rows above the base level. There is a trade-off in discarding too much data, which may result in rebuilding almost the entire tree when it's needed. The other extreme is discarding too few rows, which results in higher utilization of disk space. The default value is chosen to carefully balance this trade-off, but you may tune it as needed for your local hardware configuration. To adjust this value, use the environment variable

FIL_PROOFS_ROWS_TO_DISCARD=N

Note that if you modify this value and seal sectors using it, it CANNOT be modified without updating all previously sealed sectors (or alternatively, discarding all previously sealed sectors). A tool is provided for this conversion, but it's considered an expensive operation and should be carefully planned and completed before restarting any nodes with the new setting. The reason for this is because all 'tree_r_last' trees must be rebuilt from the sealed replica file(s) with the new target value of FIL_PROOFS_ROWS_TO_DISCARD in order to make sure that the system is consistent.

Adjusting this setting is NOT recommended unless you understand the implications of modification.

Generate Documentation

First, navigate to the rust-fil-proofs directory.

• If you cloned rust-fil-proofs manually, it will be wherever you cloned it:

> git clone https://github.com/filecoin-project/rust-fil-proofs.git
> cd rust-fil-proofs

For documentation corresponding to the latest source, you should clone rust-fil-proofs yourself.

Now, generate the documentation:

> cargo doc --all --no-deps

View the docs by pointing your browser at: …/rust-fil-proofs/target/doc/proofs/index.html.

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API Reference

The FPS is accessed from lotus via FFI calls to its API, which is the union of the APIs of its constituents:

The source of truth defining the FPS APIs is a separate repository of Rust source code. View the source directly:

• filecoin-proofs-api

The above referenced repository contains the consumer facing API and it provides a versioned wrapper around the rust-fil-proofs repository's internal APIs. End users should not be using the internal APIs of rust-fil-proofs directly, as they are subject to change outside of the formal API provided.

To generate the API documentation locally, follow the instructions to generate documentation above. Then navigate to:

• Filecoin Proofs API: …/rust-filecoin-proofs-api/target/doc/filecoin_proofs_api/index.html

• Go implementation of filecoin-proofs sectorbuilder API and associated interface structures.

Building for Arm64

In order to build for arm64 the current requirements are

• nightly rust compiler

Example for building filecoin-proofs

$ rustup +nightly target add aarch64-unknown-linux-gnu
$ cargo +nightly build -p filecoin-proofs --release --target aarch64-unknown-linux-gnu

Contributing

See Contributing

License

The Filecoin Project is dual-licensed under Apache 2.0 and MIT terms:

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)