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[thirdparty/git.git] / pack-revindex.h
1 #ifndef PACK_REVINDEX_H
2 #define PACK_REVINDEX_H
3
4 /**
5 * A revindex allows converting efficiently between three properties
6 * of an object within a pack:
7 *
8 * - index position: the numeric position within the list of sorted object ids
9 * found in the .idx file
10 *
11 * - pack position: the numeric position within the list of objects in their
12 * order within the actual .pack file (i.e., 0 is the first object in the
13 * .pack, 1 is the second, and so on)
14 *
15 * - offset: the byte offset within the .pack file at which the object contents
16 * can be found
17 *
18 * The revindex can also be used with a multi-pack index (MIDX). In this
19 * setting:
20 *
21 * - index position refers to an object's numeric position within the MIDX
22 *
23 * - pack position refers to an object's position within a non-existent pack
24 * described by the MIDX. The pack structure is described in
25 * gitformat-pack(5).
26 *
27 * It is effectively a concatanation of all packs in the MIDX (ordered by
28 * their numeric ID within the MIDX) in their original order within each
29 * pack), removing duplicates, and placing the preferred pack (if any)
30 * first.
31 */
32
33
34 #define RIDX_SIGNATURE 0x52494458 /* "RIDX" */
35 #define RIDX_VERSION 1
36
37 #define GIT_TEST_WRITE_REV_INDEX "GIT_TEST_WRITE_REV_INDEX"
38 #define GIT_TEST_REV_INDEX_DIE_IN_MEMORY "GIT_TEST_REV_INDEX_DIE_IN_MEMORY"
39
40 struct packed_git;
41 struct multi_pack_index;
42
43 /*
44 * load_pack_revindex populates the revindex's internal data-structures for the
45 * given pack, returning zero on success and a negative value otherwise.
46 *
47 * If a '.rev' file is present it is mmap'd, and pointers are assigned into it
48 * (instead of using the in-memory variant).
49 */
50 int load_pack_revindex(struct packed_git *p);
51
52 /*
53 * load_midx_revindex loads the '.rev' file corresponding to the given
54 * multi-pack index by mmap-ing it and assigning pointers in the
55 * multi_pack_index to point at it.
56 *
57 * A negative number is returned on error.
58 */
59 int load_midx_revindex(struct multi_pack_index *m);
60
61 /*
62 * Frees resources associated with a multi-pack reverse index.
63 *
64 * A negative number is returned on error.
65 */
66 int close_midx_revindex(struct multi_pack_index *m);
67
68 /*
69 * offset_to_pack_pos converts an object offset to a pack position. This
70 * function returns zero on success, and a negative number otherwise. The
71 * parameter 'pos' is usable only on success.
72 *
73 * If the reverse index has not yet been loaded, this function loads it lazily,
74 * and returns an negative number if an error was encountered.
75 *
76 * This function runs in time O(log N) with the number of objects in the pack.
77 */
78 int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos);
79
80 /*
81 * pack_pos_to_index converts the given pack-relative position 'pos' by
82 * returning an index-relative position.
83 *
84 * If the reverse index has not yet been loaded, or the position is out of
85 * bounds, this function aborts.
86 *
87 * This function runs in constant time.
88 */
89 uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos);
90
91 /*
92 * pack_pos_to_offset converts the given pack-relative position 'pos' into a
93 * pack offset. For a pack with 'N' objects, asking for position 'N' will return
94 * the total size (in bytes) of the pack.
95 *
96 * If the reverse index has not yet been loaded, or the position is out of
97 * bounds, this function aborts.
98 *
99 * This function runs in constant time under both in-memory and on-disk reverse
100 * indexes, but an additional step is taken to consult the corresponding .idx
101 * file when using the on-disk format.
102 */
103 off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos);
104
105 /*
106 * pack_pos_to_midx converts the object at position "pos" within the MIDX
107 * pseudo-pack into a MIDX position.
108 *
109 * If the reverse index has not yet been loaded, or the position is out of
110 * bounds, this function aborts.
111 *
112 * This function runs in constant time.
113 */
114 uint32_t pack_pos_to_midx(struct multi_pack_index *m, uint32_t pos);
115
116 /*
117 * midx_to_pack_pos converts from the MIDX-relative position at "at" to the
118 * corresponding pack position.
119 *
120 * If the reverse index has not yet been loaded, or the position is out of
121 * bounds, this function aborts.
122 *
123 * This function runs in time O(log N) with the number of objects in the MIDX.
124 */
125 int midx_to_pack_pos(struct multi_pack_index *midx, uint32_t at, uint32_t *pos);
126
127 #endif