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1 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
2 // vim: ts=8 sw=2 smarttab
4 * Ceph distributed storage system
6 * Copyright (C) 2013 Cloudwatt <libre.licensing@cloudwatt.com>
8 * Author: Loic Dachary <loic@dachary.org>
10 * This library is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU Lesser General Public
12 * License as published by the Free Software Foundation; either
13 * version 2.1 of the License, or (at your option) any later version.
17 #ifndef CEPH_ERASURE_CODE_EXAMPLE_H
18 #define CEPH_ERASURE_CODE_EXAMPLE_H
25 #include "crush/CrushWrapper.h"
26 #include "osd/osd_types.h"
27 #include "erasure-code/ErasureCode.h"
29 #define FIRST_DATA_CHUNK 0
30 #define SECOND_DATA_CHUNK 1
31 #define DATA_CHUNKS 2u
33 #define CODING_CHUNK 2
34 #define CODING_CHUNKS 1u
36 #define MINIMUM_TO_RECOVER 2u
38 class ErasureCodeExample
: public ErasureCode
{
40 ~ErasureCodeExample() override
{}
42 int create_ruleset(const string
&name
,
44 ostream
*ss
) const override
{
45 return crush
.add_simple_rule(name
, "default", "host",
46 "indep", pg_pool_t::TYPE_ERASURE
, ss
);
49 int minimum_to_decode(const set
<int> &want_to_read
,
50 const set
<int> &available_chunks
,
51 set
<int> *minimum
) override
{
52 if (includes(available_chunks
.begin(), available_chunks
.end(),
53 want_to_read
.begin(), want_to_read
.end())) {
54 *minimum
= want_to_read
;
56 } else if (available_chunks
.size() >= MINIMUM_TO_RECOVER
) {
57 *minimum
= available_chunks
;
64 int minimum_to_decode_with_cost(const set
<int> &want_to_read
,
65 const map
<int, int> &available
,
66 set
<int> *minimum
) override
{
68 // If one chunk is more expensive to fetch than the others,
69 // recover it instead. For instance, if the cost reflects the
70 // time it takes for a chunk to be retrieved from a remote
71 // OSD and if CPU is cheap, it could make sense to recover
72 // instead of fetching the chunk.
74 map
<int, int> c2c(available
);
75 if (c2c
.size() > DATA_CHUNKS
) {
76 if (c2c
[FIRST_DATA_CHUNK
] > c2c
[SECOND_DATA_CHUNK
] &&
77 c2c
[FIRST_DATA_CHUNK
] > c2c
[CODING_CHUNK
])
78 c2c
.erase(FIRST_DATA_CHUNK
);
79 else if(c2c
[SECOND_DATA_CHUNK
] > c2c
[FIRST_DATA_CHUNK
] &&
80 c2c
[SECOND_DATA_CHUNK
] > c2c
[CODING_CHUNK
])
81 c2c
.erase(SECOND_DATA_CHUNK
);
82 else if(c2c
[CODING_CHUNK
] > c2c
[FIRST_DATA_CHUNK
] &&
83 c2c
[CODING_CHUNK
] > c2c
[SECOND_DATA_CHUNK
])
84 c2c
.erase(CODING_CHUNK
);
86 set
<int> available_chunks
;
87 for (map
<int, int>::const_iterator i
= c2c
.begin();
90 available_chunks
.insert(i
->first
);
91 return minimum_to_decode(want_to_read
, available_chunks
, minimum
);
94 unsigned int get_chunk_count() const override
{
95 return DATA_CHUNKS
+ CODING_CHUNKS
;
98 unsigned int get_data_chunk_count() const override
{
102 unsigned int get_chunk_size(unsigned int object_size
) const override
{
103 return ( object_size
/ DATA_CHUNKS
) + 1;
106 int encode(const set
<int> &want_to_encode
,
107 const bufferlist
&in
,
108 map
<int, bufferlist
> *encoded
) override
{
110 // make sure all data chunks have the same length, allocating
111 // padding if necessary.
113 unsigned int chunk_length
= get_chunk_size(in
.length());
115 unsigned int width
= get_chunk_count() * get_chunk_size(in
.length());
116 bufferptr
pad(width
- in
.length());
117 pad
.zero(0, get_data_chunk_count());
120 // compute the coding chunk with first chunk ^ second chunk
122 char *p
= out
.c_str();
123 for (unsigned i
= 0; i
< chunk_length
; i
++)
124 p
[i
+ CODING_CHUNK
* chunk_length
] =
125 p
[i
+ FIRST_DATA_CHUNK
* chunk_length
] ^
126 p
[i
+ SECOND_DATA_CHUNK
* chunk_length
];
128 // populate the bufferlist with bufferptr pointing
129 // to chunk boundaries
131 const bufferptr
&ptr
= out
.front();
132 for (set
<int>::iterator j
= want_to_encode
.begin();
133 j
!= want_to_encode
.end();
135 bufferptr
chunk(ptr
, (*j
) * chunk_length
, chunk_length
);
136 (*encoded
)[*j
].push_front(chunk
);
141 int encode_chunks(const set
<int> &want_to_encode
,
142 map
<int, bufferlist
> *encoded
) override
{
147 int decode(const set
<int> &want_to_read
,
148 const map
<int, bufferlist
> &chunks
,
149 map
<int, bufferlist
> *decoded
) override
{
151 // All chunks have the same size
153 unsigned chunk_length
= (*chunks
.begin()).second
.length();
154 for (set
<int>::iterator i
= want_to_read
.begin();
155 i
!= want_to_read
.end();
157 if (chunks
.find(*i
) != chunks
.end()) {
159 // If the chunk is available, just copy the bufferptr pointer
160 // to the decoded argument.
162 (*decoded
)[*i
] = chunks
.find(*i
)->second
;
163 } else if(chunks
.size() != 2) {
165 // If a chunk is missing and there are not enough chunks
166 // to recover, abort.
171 // No matter what the missing chunk is, XOR of the other
174 map
<int, bufferlist
>::const_iterator k
= chunks
.begin();
175 const char *a
= k
->second
.front().c_str();
177 const char *b
= k
->second
.front().c_str();
178 bufferptr
chunk(chunk_length
);
179 char *c
= chunk
.c_str();
180 for (unsigned j
= 0; j
< chunk_length
; j
++) {
183 (*decoded
)[*i
].push_front(chunk
);
189 int decode_chunks(const set
<int> &want_to_read
,
190 const map
<int, bufferlist
> &chunks
,
191 map
<int, bufferlist
> *decoded
) override
{
196 const vector
<int> &get_chunk_mapping() const override
{
197 static vector
<int> mapping
;