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 int spawn_filter(int fd_out);
53 void write_object(int id, const char *data, size_t len);
55 // Return an estimate of the size of the file.
56 size_t size_estimate();
58 void internal_write_object(const std::string &path,
59 const char *data, size_t len);
63 std::string segment_name;
67 int real_fd, filter_fd;
71 class TarSegmentStore {
73 // New segments will be stored in the given directory.
74 TarSegmentStore(const std::string &path) { this->path = path; }
75 ~TarSegmentStore() { sync(); }
77 // Writes an object to segment in the store, and returns the name
78 // (segment/object) to refer to it. The optional parameter group can be
79 // used to control object placement; objects with different group
80 // parameters are kept in separate segments.
81 ObjectReference write_object(const char *data, size_t len,
82 const std::string &group = "");
84 // Ensure all segments have been fully written.
87 // Dump statistics to stdout about how much data has been written
93 std::string name; // UUID
94 int count; // Objects written to this segment
98 std::map<std::string, struct segment_info *> segments;
100 // Ensure that all segments in the given group have been fully written.
101 void close_segment(const std::string &group);
103 // Parse an object reference string and return just the segment name
105 std::string object_reference_to_segment(const std::string &object);
108 /* An in-memory representation of an object, which can be incrementally built
109 * before it is written out to a segment. */
115 // If an object is placed in a group, it will be written out to segments
116 // only containing other objects in the same group. A group name is simply
118 //std::string get_group() const { return group; }
119 void set_group(const std::string &g) { group = g; }
121 // Data in an object must be written all at once, and cannot be generated
122 // incrementally. Data can be an arbitrary block of binary data of any
123 // size. The pointer to the data need only remain valid until write() is
125 void set_data(const char *d, size_t len) { data = d; data_len = len; }
127 // Write an object to a segment, thus making it permanent. This function
128 // can be called at most once.
129 void write(TarSegmentStore *store);
131 // Compute the checksum of an object, and include it in the object
132 // reference. This should be called after write(), and the data specified
133 // by set_data() must remain valid through the call to checksum().
136 // An object is assigned a permanent name once it has been written to a
137 // segment. Until that time, its name cannot be determined.
138 std::string get_name() const { return ref.to_string(); }
139 ObjectReference get_ref() { return ref; }
150 /* Program through which segment data is piped before being written to file. */
151 extern const char *filter_program;
153 /* Extension which should be appended to segments written out (.tar is already
154 * included; this adds to it) */
155 extern const char *filter_extension;
157 #endif // _LBS_STORE_H