1 /* LBS: An LFS-inspired filesystem backup system
2 * Copyright (C) 2006 Michael Vrable
4 * Backup data is stored in a collection of objects, which are grouped together
5 * into segments for storage purposes. This implementation of the object store
6 * is built on top of libtar, and represents segments as TAR files and objects
7 * as files within them. */
27 /* In memory datatype to represent key/value pairs of information, such as file
28 * metadata. Currently implemented as map<string, string>. */
29 typedef std::map<std::string, std::string> dictionary;
31 /* IOException will be thrown if an error occurs while reading or writing in
32 * one of the I/O wrappers. Depending upon the context; this may be fatal or
33 * not--typically, errors reading/writing the store will be serious, but errors
34 * reading an individual file are less so. */
35 class IOException : public std::exception {
39 explicit IOException(const std::string &err) { error = err; }
40 virtual ~IOException() throw () { }
41 std::string getError() const { return error; }
44 /* A simple wrapper around a single TAR file to represent a segment. Objects
45 * may only be written out all at once, since the tar header must be written
46 * first; incremental writing is not supported. */
49 Tarfile(const std::string &path, const std::string &segment);
52 void write_object(int id, const char *data, size_t len);
54 // Return an estimate of the size of the file.
55 size_t size_estimate() { return size; }
57 void internal_write_object(const std::string &path,
58 const char *data, size_t len);
62 std::string segment_name;
66 class TarSegmentStore {
68 // New segments will be stored in the given directory.
69 TarSegmentStore(const std::string &path) { this->path = path; }
70 ~TarSegmentStore() { sync(); }
72 // Writes an object to segment in the store, and returns the name
73 // (segment/object) to refer to it. The optional parameter group can be
74 // used to control object placement; objects with different group
75 // parameters are kept in separate segments.
76 ObjectReference write_object(const char *data, size_t len,
77 const std::string &group = "");
79 // Ensure all segments have been fully written.
85 std::string name; // UUID
86 int count; // Objects written to this segment
90 std::map<std::string, struct segment_info *> segments;
92 // Ensure that all segments in the given group have been fully written.
93 void close_segment(const std::string &group);
95 // Parse an object reference string and return just the segment name
97 std::string object_reference_to_segment(const std::string &object);
100 /* An in-memory representation of an object, which can be incrementally built
101 * before it is written out to a segment. */
107 // If an object is placed in a group, it will be written out to segments
108 // only containing other objects in the same group. A group name is simply
110 //std::string get_group() const { return group; }
111 void set_group(const std::string &g) { group = g; }
113 // Data in an object must be written all at once, and cannot be generated
114 // incrementally. Data can be an arbitrary block of binary data of any
115 // size. The pointer to the data need only remain valid until write() is
117 void set_data(const char *d, size_t len) { data = d; data_len = len; }
119 // Write an object to a segment, thus making it permanent. This function
120 // can be called at most once.
121 void write(TarSegmentStore *store);
123 // Compute the checksum of an object, and include it in the object
124 // reference. This should be called after write(), and the data specified
125 // by set_data() must remain valid through the call to checksum().
128 // An object is assigned a permanent name once it has been written to a
129 // segment. Until that time, its name cannot be determined.
130 std::string get_name() const { return ref.to_string(); }
131 ObjectReference get_ref() { return ref; }
142 #endif // _LBS_STORE_H