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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).
+
+----
+
+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"