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git/commit.h
Nguyễn Thái Ngọc Duy 58babfffde shallow.c: the 8 steps to select new commits for .git/shallow
Suppose a fetch or push is requested between two shallow repositories
(with no history deepening or shortening). A pack that contains
necessary objects is transferred over together with .git/shallow of
the sender. The receiver has to determine whether it needs to update
.git/shallow if new refs needs new shallow comits.

The rule here is avoid updating .git/shallow by default. But we don't
want to waste the received pack. If the pack contains two refs, one
needs new shallow commits installed in .git/shallow and one does not,
we keep the latter and reject/warn about the former.

Even if .git/shallow update is allowed, we only add shallow commits
strictly necessary for the former ref (remember the sender can send
more shallow commits than necessary) and pay attention not to
accidentally cut the receiver history short (no history shortening is
asked for)

So the steps to figure out what ref need what new shallow commits are:

1. Split the sender shallow commit list into "ours" and "theirs" list
   by has_sha1_file. Those that exist in current repo in "ours", the
   remaining in "theirs".

2. Check the receiver .git/shallow, remove from "ours" the ones that
   also exist in .git/shallow.

3. Fetch the new pack. Either install or unpack it.

4. Do has_sha1_file on "theirs" list again. Drop the ones that fail
   has_sha1_file. Obviously the new pack does not need them.

5. If the pack is kept, remove from "ours" the ones that do not exist
   in the new pack.

6. Walk the new refs to answer the question "what shallow commits,
   both ours and theirs, are required in .git/shallow in order to add
   this ref?". Shallow commits not associated to any refs are removed
   from their respective list.

7. (*) Check reachability (from the current refs) of all remaining
   commits in "ours". Those reachable are removed. We do not want to
   cut any part of our (reachable) history. We only check up
   commits. True reachability test is done by
   check_everything_connected() at the end as usual.

8. Combine the final "ours" and "theirs" and add them all to
   .git/shallow. Install new refs. The case where some hook rejects
   some refs on a push is explained in more detail in the push
   patches.

Of these steps, #6 and #7 are expensive. Both require walking through
some commits, or in the worst case all commits. And we rather avoid
them in at least common case, where the transferred pack does not
contain any shallow commits that the sender advertises. Let's look at
each scenario:

1) the sender has longer history than the receiver

   All shallow commits from the sender will be put into "theirs" list
   at step 1 because none of them exists in current repo. In the
   common case, "theirs" becomes empty at step 4 and exit early.

2) the sender has shorter history than the receiver

   All shallow commits from the sender are likely in "ours" list at
   step 1. In the common case, if the new pack is kept, we could empty
   "ours" and exit early at step 5.

   If the pack is not kept, we hit the expensive step 6 then exit
   after "ours" is emptied. There'll be only a handful of objects to
   walk in fast-forward case. If it's forced update, we may need to
   walk to the bottom.

3) the sender has same .git/shallow as the receiver

   This is similar to case 2 except that "ours" should be emptied at
   step 2 and exit early.

A fetch after "clone --depth=X" is case 1. A fetch after "clone" (from
a shallow repo) is case 3. Luckily they're cheap for the common case.

A push from "clone --depth=X" falls into case 2, which is expensive.
Some more work may be done at the sender/client side to avoid more
work on the server side: if the transferred pack does not contain any
shallow commits, send-pack should not send any shallow commits to the
receive-pack, effectively turning it into a normal push and avoid all
steps.

This patch implements all steps except #3, already handled by
fetch-pack and receive-pack, #6 and #7, which has their own patch due
to their size.

(*) in previous versions step 7 was put before step 3. I reorder it so
    that the common case that keeps the pack does not need to walk
    commits at all. In future if we implement faster commit
    reachability check (maybe with the help of pack bitmaps or commit
    cache), step 7 could become cheap and be moved up before 6 again.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2013-12-10 16:14:16 -08:00

296 lines
9.8 KiB
C

#ifndef COMMIT_H
#define COMMIT_H
#include "object.h"
#include "tree.h"
#include "strbuf.h"
#include "decorate.h"
#include "gpg-interface.h"
#include "string-list.h"
struct commit_list {
struct commit *item;
struct commit_list *next;
};
struct commit {
struct object object;
void *util;
unsigned int index;
unsigned long date;
struct commit_list *parents;
struct tree *tree;
char *buffer;
};
extern int save_commit_buffer;
extern const char *commit_type;
/* While we can decorate any object with a name, it's only used for commits.. */
extern struct decoration name_decoration;
struct name_decoration {
struct name_decoration *next;
int type;
char name[1];
};
struct commit *lookup_commit(const unsigned char *sha1);
struct commit *lookup_commit_reference(const unsigned char *sha1);
struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
int quiet);
struct commit *lookup_commit_reference_by_name(const char *name);
/*
* Look up object named by "sha1", dereference tag as necessary,
* get a commit and return it. If "sha1" does not dereference to
* a commit, use ref_name to report an error and die.
*/
struct commit *lookup_commit_or_die(const unsigned char *sha1, const char *ref_name);
int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size);
int parse_commit(struct commit *item);
/* Find beginning and length of commit subject. */
int find_commit_subject(const char *commit_buffer, const char **subject);
struct commit_list *commit_list_insert(struct commit *item,
struct commit_list **list);
struct commit_list **commit_list_append(struct commit *commit,
struct commit_list **next);
unsigned commit_list_count(const struct commit_list *l);
struct commit_list *commit_list_insert_by_date(struct commit *item,
struct commit_list **list);
void commit_list_sort_by_date(struct commit_list **list);
/* Shallow copy of the input list */
struct commit_list *copy_commit_list(struct commit_list *list);
void free_commit_list(struct commit_list *list);
/* Commit formats */
enum cmit_fmt {
CMIT_FMT_RAW,
CMIT_FMT_MEDIUM,
CMIT_FMT_DEFAULT = CMIT_FMT_MEDIUM,
CMIT_FMT_SHORT,
CMIT_FMT_FULL,
CMIT_FMT_FULLER,
CMIT_FMT_ONELINE,
CMIT_FMT_EMAIL,
CMIT_FMT_USERFORMAT,
CMIT_FMT_UNSPECIFIED
};
struct pretty_print_context {
/*
* Callers should tweak these to change the behavior of pp_* functions.
*/
enum cmit_fmt fmt;
int abbrev;
const char *subject;
const char *after_subject;
int preserve_subject;
enum date_mode date_mode;
unsigned date_mode_explicit:1;
int need_8bit_cte;
char *notes_message;
struct reflog_walk_info *reflog_info;
const char *output_encoding;
struct string_list *mailmap;
int color;
struct ident_split *from_ident;
/*
* Fields below here are manipulated internally by pp_* functions and
* should not be counted on by callers.
*/
struct string_list in_body_headers;
};
struct userformat_want {
unsigned notes:1;
};
extern int has_non_ascii(const char *text);
struct rev_info; /* in revision.h, it circularly uses enum cmit_fmt */
extern char *logmsg_reencode(const struct commit *commit,
char **commit_encoding,
const char *output_encoding);
extern void logmsg_free(char *msg, const struct commit *commit);
extern void get_commit_format(const char *arg, struct rev_info *);
extern const char *format_subject(struct strbuf *sb, const char *msg,
const char *line_separator);
extern void userformat_find_requirements(const char *fmt, struct userformat_want *w);
extern void format_commit_message(const struct commit *commit,
const char *format, struct strbuf *sb,
const struct pretty_print_context *context);
extern void pretty_print_commit(struct pretty_print_context *pp,
const struct commit *commit,
struct strbuf *sb);
extern void pp_commit_easy(enum cmit_fmt fmt, const struct commit *commit,
struct strbuf *sb);
void pp_user_info(struct pretty_print_context *pp,
const char *what, struct strbuf *sb,
const char *line, const char *encoding);
void pp_title_line(struct pretty_print_context *pp,
const char **msg_p,
struct strbuf *sb,
const char *encoding,
int need_8bit_cte);
void pp_remainder(struct pretty_print_context *pp,
const char **msg_p,
struct strbuf *sb,
int indent);
/** Removes the first commit from a list sorted by date, and adds all
* of its parents.
**/
struct commit *pop_most_recent_commit(struct commit_list **list,
unsigned int mark);
struct commit *pop_commit(struct commit_list **stack);
void clear_commit_marks(struct commit *commit, unsigned int mark);
void clear_commit_marks_many(int nr, struct commit **commit, unsigned int mark);
void clear_commit_marks_for_object_array(struct object_array *a, unsigned mark);
enum rev_sort_order {
REV_SORT_IN_GRAPH_ORDER = 0,
REV_SORT_BY_COMMIT_DATE,
REV_SORT_BY_AUTHOR_DATE
};
/*
* Performs an in-place topological sort of list supplied.
*
* invariant of resulting list is:
* a reachable from b => ord(b) < ord(a)
* sort_order further specifies:
* REV_SORT_IN_GRAPH_ORDER: try to show a commit on a single-parent
* chain together.
* REV_SORT_BY_COMMIT_DATE: show eligible commits in committer-date order.
*/
void sort_in_topological_order(struct commit_list **, enum rev_sort_order);
struct commit_graft {
unsigned char sha1[20];
int nr_parent; /* < 0 if shallow commit */
unsigned char parent[FLEX_ARRAY][20]; /* more */
};
typedef int (*each_commit_graft_fn)(const struct commit_graft *, void *);
struct commit_graft *read_graft_line(char *buf, int len);
int register_commit_graft(struct commit_graft *, int);
struct commit_graft *lookup_commit_graft(const unsigned char *sha1);
extern struct commit_list *get_merge_bases(struct commit *rev1, struct commit *rev2, int cleanup);
extern struct commit_list *get_merge_bases_many(struct commit *one, int n, struct commit **twos, int cleanup);
extern struct commit_list *get_octopus_merge_bases(struct commit_list *in);
/* largest positive number a signed 32-bit integer can contain */
#define INFINITE_DEPTH 0x7fffffff
struct sha1_array;
struct ref;
extern int register_shallow(const unsigned char *sha1);
extern int unregister_shallow(const unsigned char *sha1);
extern int for_each_commit_graft(each_commit_graft_fn, void *);
extern int is_repository_shallow(void);
extern struct commit_list *get_shallow_commits(struct object_array *heads,
int depth, int shallow_flag, int not_shallow_flag);
extern void check_shallow_file_for_update(void);
extern void set_alternate_shallow_file(const char *path);
extern int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
const struct sha1_array *extra);
extern void setup_alternate_shallow(struct lock_file *shallow_lock,
const char **alternate_shallow_file,
const struct sha1_array *extra);
extern char *setup_temporary_shallow(const struct sha1_array *extra);
extern void advertise_shallow_grafts(int);
struct shallow_info {
struct sha1_array *shallow;
int *ours, nr_ours;
int *theirs, nr_theirs;
struct sha1_array *ref;
};
extern void prepare_shallow_info(struct shallow_info *, struct sha1_array *);
extern void clear_shallow_info(struct shallow_info *);
extern void remove_nonexistent_theirs_shallow(struct shallow_info *);
extern void remove_nonexistent_ours_in_pack(struct shallow_info *,
struct packed_git *);
int is_descendant_of(struct commit *, struct commit_list *);
int in_merge_bases(struct commit *, struct commit *);
int in_merge_bases_many(struct commit *, int, struct commit **);
extern int interactive_add(int argc, const char **argv, const char *prefix, int patch);
extern int run_add_interactive(const char *revision, const char *patch_mode,
const struct pathspec *pathspec);
static inline int single_parent(struct commit *commit)
{
return commit->parents && !commit->parents->next;
}
struct commit_list *reduce_heads(struct commit_list *heads);
struct commit_extra_header {
struct commit_extra_header *next;
char *key;
char *value;
size_t len;
};
extern void append_merge_tag_headers(struct commit_list *parents,
struct commit_extra_header ***tail);
extern int commit_tree(const struct strbuf *msg, unsigned char *tree,
struct commit_list *parents, unsigned char *ret,
const char *author, const char *sign_commit);
extern int commit_tree_extended(const struct strbuf *msg, unsigned char *tree,
struct commit_list *parents, unsigned char *ret,
const char *author, const char *sign_commit,
struct commit_extra_header *);
extern struct commit_extra_header *read_commit_extra_headers(struct commit *, const char **);
extern void free_commit_extra_headers(struct commit_extra_header *extra);
struct merge_remote_desc {
struct object *obj; /* the named object, could be a tag */
const char *name;
};
#define merge_remote_util(commit) ((struct merge_remote_desc *)((commit)->util))
/*
* Given "name" from the command line to merge, find the commit object
* and return it, while storing merge_remote_desc in its ->util field,
* to allow callers to tell if we are told to merge a tag.
*/
struct commit *get_merge_parent(const char *name);
extern int parse_signed_commit(const unsigned char *sha1,
struct strbuf *message, struct strbuf *signature);
extern void print_commit_list(struct commit_list *list,
const char *format_cur,
const char *format_last);
/*
* Check the signature of the given commit. The result of the check is stored
* in sig->check_result, 'G' for a good signature, 'U' for a good signature
* from an untrusted signer, 'B' for a bad signature and 'N' for no signature
* at all. This may allocate memory for sig->gpg_output, sig->gpg_status,
* sig->signer and sig->key.
*/
extern void check_commit_signature(const struct commit* commit, struct signature_check *sigc);
int compare_commits_by_commit_date(const void *a_, const void *b_, void *unused);
#endif /* COMMIT_H */