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