openstack/liberasurecode
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liberasurecode/README.md
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liberasurecode
==============
liberasurecode is an Erasure Code API library written in C with pluggable Erasure Code backends.
----
Highlights
==========
* Unified Erasure Coding interface for common storage workloads.
* Pluggable Erasure Code backends - As of v1.0, liberasurecode supports the following backends:
- 'Jerasure' - Erasure Coding library that supports Reed-Solomon, Cauchy backends [1]
- 'ISA-L' - Intel Storage Acceleration Library - SIMD accelerated Erasure Coding backends [2]
- 'SHSS' - NTT Lab Japan's hybrid Erasure Coding backend [4]
- 'Flat XOR HD' - built-in to liberasurecode, based on [3]
- 'NULL' template backend implemented to help future backend writers
* True 'plugin' architecture - liberasurecode uses Dynamically Loaded (DL) libraries to realize a true 'plugin' architecture. This also allows one to build liberasurecode indepdendent of the Erasure Code backend libraries.
* Cross-platform - liberasurecode is known to work on Linux (Fedora/Debian flavors), Solaris, BSD and Darwin/Mac OS X.
* Community support - Developed alongside Erasure Code authority Kevin Greenan, liberasurecode is an actively maintained open-source project with growing community involvement (Openstack Swift, Ceph, PyECLib, NTT Labs).
----
License
==========
liberasurecode is distributed under the terms of the **BSD** license.
----
Active Users
====================
* PyECLib - Python EC library: https://pypi.python.org/pypi/PyECLib
* Openstack Swift Object Store - https://wiki.openstack.org/wiki/Swift
----
liberasurecode API Definition
=============================
``` c
/* liberasurecode frontend API functions */
/**
* Create a liberasurecode instance and return a descriptor
* for use with EC operations (encode, decode, reconstruct)
*
* @param id - one of the supported backends as
* defined by ec_backend_id_t
* @param ec_args - arguments to the EC backend
* arguments common to all backends
* k - number of data fragments
* m - number of parity fragments
* w - word size, in bits
* hd - hamming distance (=m for Reed-Solomon)
* ct - fragment checksum type (stored with the fragment metadata)
* backend-specific arguments
* null_args - arguments for the null backend
* flat_xor_hd, jerasure do not require any special args
*
* @return liberasurecode instance descriptor (int > 0)
*/
int liberasurecode_instance_create(const ec_backend_id_t id,
struct ec_args *args);
/**
* Close a liberasurecode instance
*
* @param desc - liberasurecode descriptor to close
*
* @return 0 on success, otherwise non-zero error code
*/
int liberasurecode_instance_destroy(int desc);
/**
* Erasure encode a data buffer
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param orig_data - data to encode
* @param orig_data_size - length of data to encode
* @param encoded_data - pointer to _output_ array (char **) of k data
* fragments (char *), allocated by the callee
* @param encoded_parity - pointer to _output_ array (char **) of m parity
* fragments (char *), allocated by the callee
* @param fragment_len - pointer to _output_ length of each fragment, assuming
* all fragments are the same length
*
* @return 0 on success, -error code otherwise
*/
int liberasurecode_encode(int desc,
const char *orig_data, uint64_t orig_data_size, /* input */
char ***encoded_data, char ***encoded_parity, /* output */
uint64_t *fragment_len); /* output */
/**
* Cleanup structures allocated by librasurecode_encode
*
* The caller has no context, so cannot safely free memory
* allocated by liberasurecode, so it must pass the
* deallocation responsibility back to liberasurecode.
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param encoded_data - (char **) array of k data
* fragments (char *), allocated by liberasurecode_encode
* @param encoded_parity - (char **) array of m parity
* fragments (char *), allocated by liberasurecode_encode
*
* @return 0 in success; -error otherwise
*/
int liberasurecode_encode_cleanup(int desc, char **encoded_data,
char **encoded_parity);
/**
* Reconstruct original data from a set of k encoded fragments
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param fragments - erasure encoded fragments (> = k)
* @param num_fragments - number of fragments being passed in
* @param fragment_len - length of each fragment (assume they are the same)
* @param force_metadata_checks - force fragment metadata checks (default: 0)
* @param out_data - _output_ pointer to decoded data
* @param out_data_len - _output_ length of decoded output
* (both output data pointers are allocated by liberasurecode,
* caller invokes liberasurecode_decode_clean() after it has
* read decoded data in 'out_data')
*
* @return 0 on success, -error code otherwise
*/
int liberasurecode_decode(int desc,
char **available_fragments, /* input */
int num_fragments, uint64_t fragment_len, /* input */
int force_metadata_checks, /* input */
char **out_data, uint64_t *out_data_len); /* output */
/**
* Cleanup structures allocated by librasurecode_decode
*
* The caller has no context, so cannot safely free memory
* allocated by liberasurecode, so it must pass the
* deallocation responsibility back to liberasurecode.
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param data - (char *) buffer of data decoded by librasurecode_decode
*
* @return 0 on success; -error otherwise
*/
int liberasurecode_decode_cleanup(int desc, char *data);
/**
* Reconstruct a missing fragment from a subset of available fragments
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param available_fragments - erasure encoded fragments
* @param num_fragments - number of fragments being passed in
* @param fragment_len - size in bytes of the fragments
* @param destination_idx - missing idx to reconstruct
* @param out_fragment - output of reconstruct
*
* @return 0 on success, -error code otherwise
*/
int liberasurecode_reconstruct_fragment(int desc,
char **available_fragments, /* input */
int num_fragments, uint64_t fragment_len, /* input */
int destination_idx, /* input */
char* out_fragment); /* output */
/**
* Return a list of lists with valid rebuild indexes given
* a list of missing indexes.
*
* @desc: liberasurecode instance descriptor (obtained with
* liberasurecode_instance_create)
* @fragments_to_reconstruct list of indexes to reconstruct
* @fragments_to_exclude list of indexes to exclude from
* reconstruction equation
* @fragments_needed list of fragments needed to reconstruct
* fragments in fragments_to_reconstruct
*
* @return 0 on success, non-zero on error
*/
int liberasurecode_fragments_needed(int desc,
int *fragments_to_reconstruct,
int *fragments_to_exclude,
int *fragments_needed);
```
Erasure Code Fragment Checksum Types Supported
----------------------------------------------
``` c
/* Checksum types supported for fragment metadata stored in each fragment */
typedef enum {
CHKSUM_NONE = 0, /* "none" (default) */
CHKSUM_CRC32 = 1, /* "crc32" */
CHKSUM_TYPES_MAX,
} ec_checksum_type_t;
```
Erasure Code Fragment Checksum API
----------------------------------
``` c
struct __attribute__((__packed__))
fragment_metadata
{
uint32_t idx; /* 4 */
uint32_t size; /* 4 */
uint32_t frag_backend_metadata_size; /* 4 */
uint64_t orig_data_size; /* 8 */
uint8_t chksum_type; /* 1 */
uint32_t chksum[LIBERASURECODE_MAX_CHECKSUM_LEN]; /* 32 */
uint8_t chksum_mismatch; /* 1 */
uint8_t backend_id; /* 1 */
uint32_t backend_version; /* 4 */
} fragment_metadata_t;
#define FRAGSIZE_2_BLOCKSIZE(fragment_size) \
(fragment_size - sizeof(fragment_header_t))
/**
* Get opaque metadata for a fragment. The metadata is opaque to the
* client, but meaningful to the underlying library. It is used to verify
* stripes in verify_stripe_metadata().
*
* @param fragment - fragment data pointer
* @param fragment_metadata - pointer to allocated buffer of size at least
* sizeof(struct fragment_metadata) to hold fragment metadata struct
*
* @return 0 on success, non-zero on error
*/
//EDL: This needs to be implemented
int liberasurecode_get_fragment_metadata(char *fragment,
fragment_metadata_t *fragment_metadata);
/**
* Verify that the specified pointer points to a well formed fragment that can
* be processed by both this instance of liberasurecode and the specified
* backend.
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param fragment - fragment to verify
*
* @return 1 if fragment validation fails, 0 otherwise.
*/
int is_invalid_fragment(int desc, char *fragment);
/**
* Verify a subset of fragments generated by encode()
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param fragments - fragments part of the EC stripe to verify
* @param num_fragments - number of fragments part of the EC stripe
*
* @return 1 if stripe checksum verification is successful, 0 otherwise
*/
int liberasurecode_verify_stripe_metadata(int desc,
char **fragments, int num_fragments);
/* ==~=*=~===~=*=~==~=*=~== liberasurecode Helpers ==~*==~=*=~==~=~=*=~==~= */
/**
* This computes the aligned size of a buffer passed into
* the encode function. The encode function must pad fragments
* to be algined with the word size (w) and the last fragment also
* needs to be aligned. This computes the sum of the algined fragment
* sizes for a given buffer to encode.
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param data_len - original data length in bytes
*
* @return aligned length, or -error code on error
*/
int liberasurecode_get_aligned_data_size(int desc, uint64_t data_len);
/**
* This will return the minimum encode size, which is the minimum
* buffer size that can be encoded.
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
*
* @return minimum data length length, or -error code on error
*/
int liberasurecode_get_minimum_encode_size(int desc);
/**
* This will return the fragment size, which is each fragment data
* length the backend will allocate when encoding.
*
* @param desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @param data_len - original data length in bytes
*
* @return fragment size - sizeof(fragment_header) + size
* + frag_backend_metadata_size
*/
int liberasurecode_get_fragment_size(int desc, int data_len);
```
----
Build and Install
=================
To build the liberasurecode repository, perform the following from the
top-level directory:
``` sh
$ ./autogen.sh
$ ./configure
$ make
$ make test
$ sudo make install
```
----
Code organization
=================
```
|-- include
| +-- erasurecode
| | +-- erasurecode.h --> liberasurecode frontend API header
| | +-- erasurecode_backend.h --> liberasurecode backend API header
| +-- xor_codes --> headers for the built-in XOR codes
|
|-- src
| |-- erasurecode.c --> liberasurecode API implementation
| | (frontend + backend)
| |-- backends
| | +-- null
| | +--- null.c --> 'null' erasure code backend (template backend)
| | +-- xor
| | +--- flat_xor_hd.c --> 'flat_xor_hd' erasure code backend (built-in)
| | +-- jerasure
| | +-- jerasure_rs_cauchy.c --> 'jerasure_rs_vand' erasure code backend (jerasure.org)
| | +-- jerasure_rs_vand.c --> 'jerasure_rs_cauchy' erasure code backend (jerasure.org)
| | +-- isa-l
| | +-- isa_l_rs_vand.c --> 'isa_l_rs_vand' erasure code backend (Intel)
| | +-- shss
| | +-- shss.c --> 'shss' erasure code backend (NTT Labs)
| |
| |-- builtin
| | +-- xor_codes --> XOR HD code backend, built-in erasure
| | | code implementation (shared library)
| | +-- xor_code.c
| | +-- xor_hd_code.c
| |
| +-- utils
| +-- chksum --> fragment checksum utils for erasure
| +-- alg_sig.c coded fragments
| +-- crc32.c
|
|-- doc --> API Documentation
| +-- Doxyfile
| +-- html
|
|--- test --> Test routines
| +-- builtin
| | +-- xor_codes
| +-- liberasurecode_test.c
| +-- utils
|
|-- autogen.sh
|-- configure.ac
|-- Makefile.am
|-- README
|-- NEWS
|-- COPYING
|-- AUTHORS
|-- INSTALL
+-- ChangeLog
```
---
References
==========
[1] Jerasure, C library that supports erasure coding in storage applications, http://jerasure.org
[2] Intel(R) Storage Acceleration Library (Open Source Version), https://01.org/intel%C2%AE-storage-acceleration-library-open-source-version
[3] Greenan, Kevin M et al, "Flat XOR-based erasure codes in storage systems", http://www.kaymgee.com/Kevin_Greenan/Publications_files/greenan-msst10.pdf
[4] Kota Tsuyuzaki <tsuyuzaki.kota@lab.ntt.co.jp>, Ryuta Kon <kon.ryuta@po.ntts.co.jp>, "NTT SHSS Erasure Coding backend"
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