--- /dev/null
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph distributed storage system
+ *
+ * Copyright (C) 2013 Cloudwatt <libre.licensing@cloudwatt.com>
+ *
+ * Author: Loic Dachary <loic@dachary.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ */
+
+#ifndef CEPH_ERASURE_CODE_EXAMPLE_H
+#define CEPH_ERASURE_CODE_EXAMPLE_H
+
+#include <unistd.h>
+#include <errno.h>
+#include <algorithm>
+#include <sstream>
+
+#include "crush/CrushWrapper.h"
+#include "osd/osd_types.h"
+#include "erasure-code/ErasureCode.h"
+
+#define FIRST_DATA_CHUNK 0
+#define SECOND_DATA_CHUNK 1
+#define DATA_CHUNKS 2u
+
+#define CODING_CHUNK 2
+#define CODING_CHUNKS 1u
+
+#define MINIMUM_TO_RECOVER 2u
+
+class ErasureCodeExample : public ErasureCode {
+public:
+ ~ErasureCodeExample() override {}
+
+ int create_rule(const string &name,
+ CrushWrapper &crush,
+ ostream *ss) const override {
+ return crush.add_simple_rule(name, "default", "host", "",
+ "indep", pg_pool_t::TYPE_ERASURE, ss);
+ }
+
+ int minimum_to_decode(const set<int> &want_to_read,
+ const set<int> &available_chunks,
+ set<int> *minimum) override {
+ if (includes(available_chunks.begin(), available_chunks.end(),
+ want_to_read.begin(), want_to_read.end())) {
+ *minimum = want_to_read;
+ return 0;
+ } else if (available_chunks.size() >= MINIMUM_TO_RECOVER) {
+ *minimum = available_chunks;
+ return 0;
+ } else {
+ return -EIO;
+ }
+ }
+
+ int minimum_to_decode_with_cost(const set<int> &want_to_read,
+ const map<int, int> &available,
+ set<int> *minimum) override {
+ //
+ // If one chunk is more expensive to fetch than the others,
+ // recover it instead. For instance, if the cost reflects the
+ // time it takes for a chunk to be retrieved from a remote
+ // OSD and if CPU is cheap, it could make sense to recover
+ // instead of fetching the chunk.
+ //
+ map<int, int> c2c(available);
+ if (c2c.size() > DATA_CHUNKS) {
+ if (c2c[FIRST_DATA_CHUNK] > c2c[SECOND_DATA_CHUNK] &&
+ c2c[FIRST_DATA_CHUNK] > c2c[CODING_CHUNK])
+ c2c.erase(FIRST_DATA_CHUNK);
+ else if(c2c[SECOND_DATA_CHUNK] > c2c[FIRST_DATA_CHUNK] &&
+ c2c[SECOND_DATA_CHUNK] > c2c[CODING_CHUNK])
+ c2c.erase(SECOND_DATA_CHUNK);
+ else if(c2c[CODING_CHUNK] > c2c[FIRST_DATA_CHUNK] &&
+ c2c[CODING_CHUNK] > c2c[SECOND_DATA_CHUNK])
+ c2c.erase(CODING_CHUNK);
+ }
+ set <int> available_chunks;
+ for (map<int, int>::const_iterator i = c2c.begin();
+ i != c2c.end();
+ ++i)
+ available_chunks.insert(i->first);
+ return minimum_to_decode(want_to_read, available_chunks, minimum);
+ }
+
+ unsigned int get_chunk_count() const override {
+ return DATA_CHUNKS + CODING_CHUNKS;
+ }
+
+ unsigned int get_data_chunk_count() const override {
+ return DATA_CHUNKS;
+ }
+
+ unsigned int get_chunk_size(unsigned int object_size) const override {
+ return ( object_size / DATA_CHUNKS ) + 1;
+ }
+
+ int encode(const set<int> &want_to_encode,
+ const bufferlist &in,
+ map<int, bufferlist> *encoded) override {
+ //
+ // make sure all data chunks have the same length, allocating
+ // padding if necessary.
+ //
+ unsigned int chunk_length = get_chunk_size(in.length());
+ bufferlist out(in);
+ unsigned int width = get_chunk_count() * get_chunk_size(in.length());
+ bufferptr pad(width - in.length());
+ pad.zero(0, get_data_chunk_count());
+ out.push_back(pad);
+ //
+ // compute the coding chunk with first chunk ^ second chunk
+ //
+ char *p = out.c_str();
+ for (unsigned i = 0; i < chunk_length; i++)
+ p[i + CODING_CHUNK * chunk_length] =
+ p[i + FIRST_DATA_CHUNK * chunk_length] ^
+ p[i + SECOND_DATA_CHUNK * chunk_length];
+ //
+ // populate the bufferlist with bufferptr pointing
+ // to chunk boundaries
+ //
+ const bufferptr &ptr = out.front();
+ for (set<int>::iterator j = want_to_encode.begin();
+ j != want_to_encode.end();
+ ++j) {
+ bufferptr chunk(ptr, (*j) * chunk_length, chunk_length);
+ (*encoded)[*j].push_front(chunk);
+ }
+ return 0;
+ }
+
+ int encode_chunks(const set<int> &want_to_encode,
+ map<int, bufferlist> *encoded) override {
+ ceph_abort();
+ return 0;
+ }
+
+ int decode(const set<int> &want_to_read,
+ const map<int, bufferlist> &chunks,
+ map<int, bufferlist> *decoded) override {
+ //
+ // All chunks have the same size
+ //
+ unsigned chunk_length = (*chunks.begin()).second.length();
+ for (set<int>::iterator i = want_to_read.begin();
+ i != want_to_read.end();
+ ++i) {
+ if (chunks.find(*i) != chunks.end()) {
+ //
+ // If the chunk is available, just copy the bufferptr pointer
+ // to the decoded argument.
+ //
+ (*decoded)[*i] = chunks.find(*i)->second;
+ } else if(chunks.size() != 2) {
+ //
+ // If a chunk is missing and there are not enough chunks
+ // to recover, abort.
+ //
+ return -ERANGE;
+ } else {
+ //
+ // No matter what the missing chunk is, XOR of the other
+ // two recovers it.
+ //
+ map<int, bufferlist>::const_iterator k = chunks.begin();
+ const char *a = k->second.front().c_str();
+ ++k;
+ const char *b = k->second.front().c_str();
+ bufferptr chunk(chunk_length);
+ char *c = chunk.c_str();
+ for (unsigned j = 0; j < chunk_length; j++) {
+ c[j] = a[j] ^ b[j];
+ }
+ (*decoded)[*i].push_front(chunk);
+ }
+ }
+ return 0;
+ }
+
+ int decode_chunks(const set<int> &want_to_read,
+ const map<int, bufferlist> &chunks,
+ map<int, bufferlist> *decoded) override {
+ ceph_abort();
+ return 0;
+ }
+
+ const vector<int> &get_chunk_mapping() const override {
+ static vector<int> mapping;
+ return mapping;
+ }
+
+};
+
+#endif
Code Review / stor4nfv.git / blobdiff