## Introduction
. . .
| o | |
| . |.-. .-. .--..-. .--.. . .--..-. .-..-. .-.| .-.
| | | )(.-' | ( ) `--.| | | (.-'( ( )( |(.-'
`--' `-'`-' `--'' `-'`-`--'`--`-' `--'`-'`-' `-'`-`--'
liberasurecode is an Erasure Code API library written in C. The goal of
this project is to provide a unified Erasure Coding interface with
'pluggable' Erasure Code backends.
As of v0.9.10, liberasurecode supports 'Jerasure' (Reed-Solomon, Cauchy),
'Flat XOR HD' backends. A template 'NULL' backend is implemented to help
future backend writers.
liberasurecode is designed around Dynamically Loaded (DL) libraries to
realize a true 'plugin' architecture. This also allows one to build
liberasurecode indepdendent of the Erasure Code backend libraries.
liberasurecode is known to work on Linux (Fedora/Debian flavors), Solaris,
BSD and Darwin/Mac OS X.
liberasurecode is distributed under the terms of the BSD license.
## liberasurecode Frontend API
/* =~=*=~==~=*=~==~=*=~= Supported EC backends =~=*=~==~=*=~==~=*=~==~=*=~== */
typedef enum {
EC_BACKEND_NULL = 0,
EC_BACKEND_JERASURE_RS_VAND = 1,
EC_BACKEND_JERASURE_RS_CAUCHY = 2,
EC_BACKEND_FLAT_XOR_HD = 3,
EC_BACKENDS_MAX,
} ec_backend_id_t;
#ifndef EC_BACKENDS_SUPPORTED
#define EC_BACKENDS_SUPPORTED
/* Supported EC backends */
static const char *ec_backend_names[EC_BACKENDS_MAX] = {
"null",
"jerasure_rs_vand",
"jerasure_rs_cauchy",
"flat_xor_hd",
};
#endif // EC_BACKENDS_SUPPORTED
/* ~=*=~==~=*=~= EC Fragment metadata - supported checksum types ~=*=~==~=*=~ */
/* Checksum types supported for fragment metadata stored in each fragment */
typedef enum {
CHKSUM_NONE = 0,
CHKSUM_CRC32 = 1,
CHKSUM_MD5 = 2,
CHKSUM_TYPES_MAX,
} ec_checksum_type_t;
#ifndef EC_CHKSUM_TYPES_SUPPORTED
#define EC_CHKSUM_TYPES_SUPPORTED
/* Supported EC backends */
static const char *ec_chksum_types[CHKSUM_TYPES_MAX] = {
"none",
"crc32",
"md5",
};
#endif // EC_CHKSUM_TYPES_SUPPORTED
/* =~=*=~==~=*=~== EC Arguments - Common and backend-specific =~=*=~==~=*=~== */
/**
* Common and backend-specific args
* to be passed to liberasurecode_instance_create()
*/
struct ec_args {
int k; /* number of data fragments */
int m; /* number of parity fragments */
int w; /* word size, in bits (optional) */
int hd; /* hamming distance (=m for Reed-Solomon) */
union {
struct {
uint64_t arg1; /* sample arg */
} null_args; /* args specific to the null codes */
struct {
uint64_t x, y; /* reserved for future expansion */
uint64_t z, a; /* reserved for future expansion */
} reserved;
} priv_args1;
void *priv_args2; /** flexible placeholder for
* future backend args */
ec_checksum_type_t ct; /* fragment checksum type */
};
/* =~=*=~==~=*=~== liberasurecode frontend API functions =~=*=~==~=~=*=~==~= */
/* liberasurecode frontend API functions */
/**
* Returns a list of EC backends implemented/enabled - the user
* should always rely on the return from this function as this
* set of backends can be different from the names listed in
* ec_backend_names above.
*
* @param num_backends - pointer to int, size of list returned
*
* @return list of EC backends implemented
*/
const char ** liberasurecode_supported_backends(int *num_backends);
/**
* Returns a list of checksum types supported for fragment data, stored in
* individual fragment headers as part of fragment metadata
*
* @param num_checksum_types - pointer to int, size of list returned
*
* @return list of checksum types supported for fragment data
*/
const char ** liberasurecode_supported_checksum_types(int *num_checksum_types);
/**
* Create a liberasurecode instance and return a descriptor
* for use with EC operations (encode, decode, reconstruct)
*
* @param backend_name - one of the supported backends as
* defined by ec_backend_names
* @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 char *backend_name,
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 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 */
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);
/* ==~=*=~==~=*=~== liberasurecode fragment metadata routines ==~*==~=*=~==~ */
#define LIBERASURECODE_MAX_CHECKSUM_LEN 8
typedef struct __attribute__((__packed__))
fragment_metadata
{
uint32_t idx; /* 4 */
uint32_t 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 */
} 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 desc - liberasurecode descriptor/handle
* from liberasurecode_instance_create()
* @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
*/
int liberasurecode_get_fragment_metadata(int desc,
char *fragment, fragment_metadata_t *fragment_metadata);
/**
* 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);
/* ==~=*=~===~=*=~==~=*=~== liberasurecode Error codes =~=*=~==~=~=*=~==~== */
/* Error codes */
typedef enum {
EBACKENDNOTSUPP = 200,
EECMETHODNOTIMPL = 201,
EBACKENDINITERR = 202,
EBACKENDINUSE = 203,
EBACKENDNOTAVAIL = 204,
} LIBERASURECODE_ERROR_CODES;
/* =~=*=~==~=*=~==~=*=~==~=*=~===~=*=~==~=*=~===~=*=~==~=*=~===~=*=~==~=*=~= */
```
## 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
│ │ └── xor
│ │ └─── flat_xor_hd.c --> 'flat_xor_hd' erasure code backend
│ │ └── jerasure
│ │ ├── jerasure_rs_cauchy.c --> 'jerasure_rs_vand' erasure code backend
│ │ └── jerasure_rs_vand.c --> 'jerasure_rs_cauchy' erasure code backend
| |
│ ├── 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
```
## Build
To build the liberasurecode repository, perform the following from the
top-level directory:
`$ ./autogen.sh`
`$ ./configure`
`$ make`
`$ make test`
`$ sudo make install`
--