README -> README.md

Signed-off-by: Tushar Gohad <tushar.gohad@intel.com>

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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 v0.9.10, liberasurecode supports 'Jerasure' (Reed-Solomon, Cauchy), 'Flat XOR HD' backends.  A template 'NULL' backend is implemented to help future backend writers.  Also on the horizon is the support for - Intel Storage Acceleration Library (ISA-L) EC backend.

+

+ * 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).

+

+----

+

+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

+=============================

+----

+

+Backend Support

+---------------

+

+``` c

+/* =~=*=~==~=*=~==~=*=~= 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;

+

+/* Supported EC backends */

+static const char *ec_backend_names[EC_BACKENDS_MAX] = {

+    "null",

+    "jerasure_rs_vand",

+    "jerasure_rs_cauchy",

+    "flat_xor_hd",

+};

+```

+

+----

+

+Erasure Code Fragment Checksum Support

+--------------------------------------

+

+``` c

+

+/* ~=*=~==~=*=~= 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;

+

+/* Supported checksum types */

+static const char *ec_chksum_types[CHKSUM_TYPES_MAX] = {

+    "none",

+    "crc32",

+    "md5",

+};

+```

+----

+

+User Arguments

+--------------

+

+``` c

+/* =~=*=~==~=*=~== 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 */

+};

+```

+

+---

+

+User-facing API Functions

+-------------------------

+

+``` c

+/* =~=*=~==~=*=~== 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);

+```

+----

+

+Error Codes

+-----------

+

+``` c

+/* ==~=*=~===~=*=~==~=*=~== liberasurecode Error codes =~=*=~==~=~=*=~==~== */

+

+/* Error codes */

+typedef enum {

+    EBACKENDNOTSUPP  = 200,

+    EECMETHODNOTIMPL = 201,

+    EBACKENDINITERR  = 202,

+    EBACKENDINUSE    = 203,

+    EBACKENDNOTAVAIL = 204,

+} LIBERASURECODE_ERROR_CODES;

+

+/* =~=*=~==~=*=~==~=*=~==~=*=~===~=*=~==~=*=~===~=*=~==~=*=~===~=*=~==~=*=~= */

+```

+---

+

+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

+  │   │   └── 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

+```

+---

+