diff options
Diffstat (limited to 'Documentation/technical')
| -rw-r--r-- | Documentation/technical/api-argv-array.txt | 8 | ||||
| -rw-r--r-- | Documentation/technical/api-builtin.txt | 13 | ||||
| -rw-r--r-- | Documentation/technical/api-hash.txt | 52 | ||||
| -rw-r--r-- | Documentation/technical/api-hashmap.txt | 234 | ||||
| -rw-r--r-- | Documentation/technical/api-parse-options.txt | 4 | ||||
| -rw-r--r-- | Documentation/technical/api-run-command.txt | 7 | ||||
| -rw-r--r-- | Documentation/technical/api-strbuf.txt | 13 | ||||
| -rw-r--r-- | Documentation/technical/bitmap-format.txt | 164 | ||||
| -rw-r--r-- | Documentation/technical/http-protocol.txt | 6 |
9 files changed, 429 insertions, 72 deletions
diff --git a/Documentation/technical/api-argv-array.txt b/Documentation/technical/api-argv-array.txt index a6b7d83..1a79781 100644 --- a/Documentation/technical/api-argv-array.txt +++ b/Documentation/technical/api-argv-array.txt @@ -53,11 +53,3 @@ Functions `argv_array_clear`:: Free all memory associated with the array and return it to the initial, empty state. - -`argv_array_detach`:: - Detach the argv array from the `struct argv_array`, transferring - ownership of the allocated array and strings. - -`argv_array_free_detached`:: - Free the memory allocated by a `struct argv_array` that was later - detached and is now no longer needed. diff --git a/Documentation/technical/api-builtin.txt b/Documentation/technical/api-builtin.txt index e3d6e7a..22a39b9 100644 --- a/Documentation/technical/api-builtin.txt +++ b/Documentation/technical/api-builtin.txt @@ -22,11 +22,14 @@ Git: where options is the bitwise-or of: `RUN_SETUP`:: - - Make sure there is a Git directory to work on, and if there is a - work tree, chdir to the top of it if the command was invoked - in a subdirectory. If there is no work tree, no chdir() is - done. + If there is not a Git directory to work on, abort. If there + is a work tree, chdir to the top of it if the command was + invoked in a subdirectory. If there is no work tree, no + chdir() is done. + +`RUN_SETUP_GENTLY`:: + If there is a Git directory, chdir as per RUN_SETUP, otherwise, + don't chdir anywhere. `USE_PAGER`:: diff --git a/Documentation/technical/api-hash.txt b/Documentation/technical/api-hash.txt deleted file mode 100644 index e5061e0..0000000 --- a/Documentation/technical/api-hash.txt +++ /dev/null @@ -1,52 +0,0 @@ -hash API -======== - -The hash API is a collection of simple hash table functions. Users are expected -to implement their own hashing. - -Data Structures ---------------- - -`struct hash_table`:: - - The hash table structure. The `array` member points to the hash table - entries. The `size` member counts the total number of valid and invalid - entries in the table. The `nr` member keeps track of the number of - valid entries. - -`struct hash_table_entry`:: - - An opaque structure representing an entry in the hash table. The `hash` - member is the entry's hash key and the `ptr` member is the entry's - value. - -Functions ---------- - -`init_hash`:: - - Initialize the hash table. - -`free_hash`:: - - Release memory associated with the hash table. - -`insert_hash`:: - - Insert a pointer into the hash table. If an entry with that hash - already exists, a pointer to the existing entry's value is returned. - Otherwise NULL is returned. This allows callers to implement - chaining, etc. - -`lookup_hash`:: - - Lookup an entry in the hash table. If an entry with that hash exists - the entry's value is returned. Otherwise NULL is returned. - -`for_each_hash`:: - - Call a function for each entry in the hash table. The function is - expected to take the entry's value as its only argument and return an - int. If the function returns a negative int the loop is aborted - immediately. Otherwise, the return value is accumulated and the sum - returned upon completion of the loop. diff --git a/Documentation/technical/api-hashmap.txt b/Documentation/technical/api-hashmap.txt new file mode 100644 index 0000000..b977ae8 --- /dev/null +++ b/Documentation/technical/api-hashmap.txt @@ -0,0 +1,234 @@ +hashmap API +=========== + +The hashmap API is a generic implementation of hash-based key-value mappings. + +Data Structures +--------------- + +`struct hashmap`:: + + The hash table structure. ++ +The `size` member keeps track of the total number of entries. The `cmpfn` +member is a function used to compare two entries for equality. The `table` and +`tablesize` members store the hash table and its size, respectively. + +`struct hashmap_entry`:: + + An opaque structure representing an entry in the hash table, which must + be used as first member of user data structures. Ideally it should be + followed by an int-sized member to prevent unused memory on 64-bit + systems due to alignment. ++ +The `hash` member is the entry's hash code and the `next` member points to the +next entry in case of collisions (i.e. if multiple entries map to the same +bucket). + +`struct hashmap_iter`:: + + An iterator structure, to be used with hashmap_iter_* functions. + +Types +----- + +`int (*hashmap_cmp_fn)(const void *entry, const void *entry_or_key, const void *keydata)`:: + + User-supplied function to test two hashmap entries for equality. Shall + return 0 if the entries are equal. ++ +This function is always called with non-NULL `entry` / `entry_or_key` +parameters that have the same hash code. When looking up an entry, the `key` +and `keydata` parameters to hashmap_get and hashmap_remove are always passed +as second and third argument, respectively. Otherwise, `keydata` is NULL. + +Functions +--------- + +`unsigned int strhash(const char *buf)`:: +`unsigned int strihash(const char *buf)`:: +`unsigned int memhash(const void *buf, size_t len)`:: +`unsigned int memihash(const void *buf, size_t len)`:: + + Ready-to-use hash functions for strings, using the FNV-1 algorithm (see + http://www.isthe.com/chongo/tech/comp/fnv). ++ +`strhash` and `strihash` take 0-terminated strings, while `memhash` and +`memihash` operate on arbitrary-length memory. ++ +`strihash` and `memihash` are case insensitive versions. + +`void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function, size_t initial_size)`:: + + Initializes a hashmap structure. ++ +`map` is the hashmap to initialize. ++ +The `equals_function` can be specified to compare two entries for equality. +If NULL, entries are considered equal if their hash codes are equal. ++ +If the total number of entries is known in advance, the `initial_size` +parameter may be used to preallocate a sufficiently large table and thus +prevent expensive resizing. If 0, the table is dynamically resized. + +`void hashmap_free(struct hashmap *map, int free_entries)`:: + + Frees a hashmap structure and allocated memory. ++ +`map` is the hashmap to free. ++ +If `free_entries` is true, each hashmap_entry in the map is freed as well +(using stdlib's free()). + +`void hashmap_entry_init(void *entry, unsigned int hash)`:: + + Initializes a hashmap_entry structure. ++ +`entry` points to the entry to initialize. ++ +`hash` is the hash code of the entry. + +`void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)`:: + + Returns the hashmap entry for the specified key, or NULL if not found. ++ +`map` is the hashmap structure. ++ +`key` is a hashmap_entry structure (or user data structure that starts with +hashmap_entry) that has at least been initialized with the proper hash code +(via `hashmap_entry_init`). ++ +If an entry with matching hash code is found, `key` and `keydata` are passed +to `hashmap_cmp_fn` to decide whether the entry matches the key. + +`void *hashmap_get_next(const struct hashmap *map, const void *entry)`:: + + Returns the next equal hashmap entry, or NULL if not found. This can be + used to iterate over duplicate entries (see `hashmap_add`). ++ +`map` is the hashmap structure. ++ +`entry` is the hashmap_entry to start the search from, obtained via a previous +call to `hashmap_get` or `hashmap_get_next`. + +`void hashmap_add(struct hashmap *map, void *entry)`:: + + Adds a hashmap entry. This allows to add duplicate entries (i.e. + separate values with the same key according to hashmap_cmp_fn). ++ +`map` is the hashmap structure. ++ +`entry` is the entry to add. + +`void *hashmap_put(struct hashmap *map, void *entry)`:: + + Adds or replaces a hashmap entry. If the hashmap contains duplicate + entries equal to the specified entry, only one of them will be replaced. ++ +`map` is the hashmap structure. ++ +`entry` is the entry to add or replace. ++ +Returns the replaced entry, or NULL if not found (i.e. the entry was added). + +`void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)`:: + + Removes a hashmap entry matching the specified key. If the hashmap + contains duplicate entries equal to the specified key, only one of + them will be removed. ++ +`map` is the hashmap structure. ++ +`key` is a hashmap_entry structure (or user data structure that starts with +hashmap_entry) that has at least been initialized with the proper hash code +(via `hashmap_entry_init`). ++ +If an entry with matching hash code is found, `key` and `keydata` are +passed to `hashmap_cmp_fn` to decide whether the entry matches the key. ++ +Returns the removed entry, or NULL if not found. + +`void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)`:: +`void *hashmap_iter_next(struct hashmap_iter *iter)`:: +`void *hashmap_iter_first(struct hashmap *map, struct hashmap_iter *iter)`:: + + Used to iterate over all entries of a hashmap. ++ +`hashmap_iter_init` initializes a `hashmap_iter` structure. ++ +`hashmap_iter_next` returns the next hashmap_entry, or NULL if there are no +more entries. ++ +`hashmap_iter_first` is a combination of both (i.e. initializes the iterator +and returns the first entry, if any). + +Usage example +------------- + +Here's a simple usage example that maps long keys to double values. +------------ +struct hashmap map; + +struct long2double { + struct hashmap_entry ent; /* must be the first member! */ + long key; + double value; +}; + +static int long2double_cmp(const struct long2double *e1, const struct long2double *e2, const void *unused) +{ + return !(e1->key == e2->key); +} + +void long2double_init(void) +{ + hashmap_init(&map, (hashmap_cmp_fn) long2double_cmp, 0); +} + +void long2double_free(void) +{ + hashmap_free(&map, 1); +} + +static struct long2double *find_entry(long key) +{ + struct long2double k; + hashmap_entry_init(&k, memhash(&key, sizeof(long))); + k.key = key; + return hashmap_get(&map, &k, NULL); +} + +double get_value(long key) +{ + struct long2double *e = find_entry(key); + return e ? e->value : 0; +} + +void set_value(long key, double value) +{ + struct long2double *e = find_entry(key); + if (!e) { + e = malloc(sizeof(struct long2double)); + hashmap_entry_init(e, memhash(&key, sizeof(long))); + e->key = key; + hashmap_add(&map, e); + } + e->value = value; +} +------------ + +Using variable-sized keys +------------------------- + +The `hashmap_entry_get` and `hashmap_entry_remove` functions expect an ordinary +`hashmap_entry` structure as key to find the correct entry. If the key data is +variable-sized (e.g. a FLEX_ARRAY string) or quite large, it is undesirable +to create a full-fledged entry structure on the heap and copy all the key data +into the structure. + +In this case, the `keydata` parameter can be used to pass +variable-sized key data directly to the comparison function, and the `key` +parameter can be a stripped-down, fixed size entry structure allocated on the +stack. + +See test-hashmap.c for an example using arbitrary-length strings as keys. diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt index be50cf4..1f2db31 100644 --- a/Documentation/technical/api-parse-options.txt +++ b/Documentation/technical/api-parse-options.txt @@ -160,10 +160,6 @@ There are some macros to easily define options: `int_var` is set to `integer` with `--option`, and reset to zero with `--no-option`. -`OPT_SET_PTR(short, long, &ptr_var, description, ptr)`:: - Introduce a boolean option. - If used, set `ptr_var` to `ptr`. - `OPT_STRING(short, long, &str_var, arg_str, description)`:: Introduce an option with string argument. The string argument is put into `str_var`. diff --git a/Documentation/technical/api-run-command.txt b/Documentation/technical/api-run-command.txt index 5d7d7f2..69510ae 100644 --- a/Documentation/technical/api-run-command.txt +++ b/Documentation/technical/api-run-command.txt @@ -109,6 +109,13 @@ terminated), of which .argv[0] is the program name to run (usually without a path). If the command to run is a git command, set argv[0] to the command name without the 'git-' prefix and set .git_cmd = 1. +Note that the ownership of the memory pointed to by .argv stays with the +caller, but it should survive until `finish_command` completes. If the +.argv member is NULL, `start_command` will point it at the .args +`argv_array` (so you may use one or the other, but you must use exactly +one). The memory in .args will be cleaned up automatically during +`finish_command` (or during `start_command` when it is unsuccessful). + The members .in, .out, .err are used to redirect stdin, stdout, stderr as follows: diff --git a/Documentation/technical/api-strbuf.txt b/Documentation/technical/api-strbuf.txt index 3350d97..5069018 100644 --- a/Documentation/technical/api-strbuf.txt +++ b/Documentation/technical/api-strbuf.txt @@ -121,10 +121,23 @@ Functions * Related to the contents of the buffer +`strbuf_trim`:: + + Strip whitespace from the beginning and end of a string. + Equivalent to performing `strbuf_rtrim()` followed by `strbuf_ltrim()`. + `strbuf_rtrim`:: Strip whitespace from the end of a string. +`strbuf_ltrim`:: + + Strip whitespace from the beginning of a string. + +`strbuf_tolower`:: + + Lowercase each character in the buffer using `tolower`. + `strbuf_cmp`:: Compare two buffers. Returns an integer less than, equal to, or greater diff --git a/Documentation/technical/bitmap-format.txt b/Documentation/technical/bitmap-format.txt new file mode 100644 index 0000000..f8c18a0 --- /dev/null +++ b/Documentation/technical/bitmap-format.txt @@ -0,0 +1,164 @@ +GIT bitmap v1 format +==================== + + - A header appears at the beginning: + + 4-byte signature: {'B', 'I', 'T', 'M'} + + 2-byte version number (network byte order) + The current implementation only supports version 1 + of the bitmap index (the same one as JGit). + + 2-byte flags (network byte order) + + The following flags are supported: + + - BITMAP_OPT_FULL_DAG (0x1) REQUIRED + This flag must always be present. It implies that the bitmap + index has been generated for a packfile with full closure + (i.e. where every single object in the packfile can find + its parent links inside the same packfile). This is a + requirement for the bitmap index format, also present in JGit, + that greatly reduces the complexity of the implementation. + + - BITMAP_OPT_HASH_CACHE (0x4) + If present, the end of the bitmap file contains + `N` 32-bit name-hash values, one per object in the + pack. The format and meaning of the name-hash is + described below. + + 4-byte entry count (network byte order) + + The total count of entries (bitmapped commits) in this bitmap index. + + 20-byte checksum + + The SHA1 checksum of the pack this bitmap index belongs to. + + - 4 EWAH bitmaps that act as type indexes + + Type indexes are serialized after the hash cache in the shape + of four EWAH bitmaps stored consecutively (see Appendix A for + the serialization format of an EWAH bitmap). + + There is a bitmap for each Git object type, stored in the following + order: + + - Commits + - Trees + - Blobs + - Tags + + In each bitmap, the `n`th bit is set to true if the `n`th object + in the packfile is of that type. + + The obvious consequence is that the OR of all 4 bitmaps will result + in a full set (all bits set), and the AND of all 4 bitmaps will + result in an empty bitmap (no bits set). + + - N entries with compressed bitmaps, one for each indexed commit + + Where `N` is the total amount of entries in this bitmap index. + Each entry contains the following: + + - 4-byte object position (network byte order) + The position **in the index for the packfile** where the + bitmap for this commit is found. + + - 1-byte XOR-offset + The xor offset used to compress this bitmap. For an entry + in position `x`, a XOR offset of `y` means that the actual + bitmap representing this commit is composed by XORing the + bitmap for this entry with the bitmap in entry `x-y` (i.e. + the bitmap `y` entries before this one). + + Note that this compression can be recursive. In order to + XOR this entry with a previous one, the previous entry needs + to be decompressed first, and so on. + + The hard-limit for this offset is 160 (an entry can only be + xor'ed against one of the 160 entries preceding it). This + number is always positive, and hence entries are always xor'ed + with **previous** bitmaps, not bitmaps that will come afterwards + in the index. + + - 1-byte flags for this bitmap + At the moment the only available flag is `0x1`, which hints + that this bitmap can be re-used when rebuilding bitmap indexes + for the repository. + + - The compressed bitmap itself, see Appendix A. + +== Appendix A: Serialization format for an EWAH bitmap + +Ewah bitmaps are serialized in the same protocol as the JAVAEWAH +library, making them backwards compatible with the JGit +implementation: + + - 4-byte number of bits of the resulting UNCOMPRESSED bitmap + + - 4-byte number of words of the COMPRESSED bitmap, when stored + + - N x 8-byte words, as specified by the previous field + + This is the actual content of the compressed bitmap. + + - 4-byte position of the current RLW for the compressed + bitmap + +All words are stored in network byte order for their corresponding +sizes. + +The compressed bitmap is stored in a form of run-length encoding, as +follows. It consists of a concatenation of an arbitrary number of +chunks. Each chunk consists of one or more 64-bit words + + H L_1 L_2 L_3 .... L_M + +H is called RLW (run length word). It consists of (from lower to higher +order bits): + + - 1 bit: the repeated bit B + + - 32 bits: repetition count K (unsigned) + + - 31 bits: literal word count M (unsigned) + +The bitstream represented by the above chunk is then: + + - K repetitions of B + + - The bits stored in `L_1` through `L_M`. Within a word, bits at + lower order come earlier in the stream than those at higher + order. + +The next word after `L_M` (if any) must again be a RLW, for the next +chunk. For efficient appending to the bitstream, the EWAH stores a +pointer to the last RLW in the stream. + + +== Appendix B: Optional Bitmap Sections + +These sections may or may not be present in the `.bitmap` file; their +presence is indicated by the header flags section described above. + +Name-hash cache +--------------- + +If the BITMAP_OPT_HASH_CACHE flag is set, the end of the bitmap contains +a cache of 32-bit values, one per object in the pack. The value at +position `i` is the hash of the pathname at which the `i`th object +(counting in index order) in the pack can be found. This can be fed +into the delta heuristics to compare objects with similar pathnames. + +The hash algorithm used is: + + hash = 0; + while ((c = *name++)) + if (!isspace(c)) + hash = (hash >> 2) + (c << 24); + +Note that this hashing scheme is tied to the BITMAP_OPT_HASH_CACHE flag. +If implementations want to choose a different hashing scheme, they are +free to do so, but MUST allocate a new header flag (because comparing +hashes made under two different schemes would be pointless). diff --git a/Documentation/technical/http-protocol.txt b/Documentation/technical/http-protocol.txt index 544373b..59be59b 100644 --- a/Documentation/technical/http-protocol.txt +++ b/Documentation/technical/http-protocol.txt @@ -374,7 +374,7 @@ C: Send one `$GIT_URL/git-upload-pack` request: C: 0000 The stream is organized into "commands", with each command -appearing by itself in a pkt-line. Within a command line +appearing by itself in a pkt-line. Within a command line, the text leading up to the first space is the command name, and the remainder of the line to the first LF is the value. Command lines are terminated with an LF as the last byte of @@ -500,7 +500,7 @@ TODO: Document this further. References ---------- -link:http://www.ietf.org/rfc/rfc1738.txt[RFC 1738: Uniform Resource Locators (URL)] -link:http://www.ietf.org/rfc/rfc2616.txt[RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1] +http://www.ietf.org/rfc/rfc1738.txt[RFC 1738: Uniform Resource Locators (URL)] +http://www.ietf.org/rfc/rfc2616.txt[RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1] link:technical/pack-protocol.html link:technical/protocol-capabilities.html |