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git/diff.h
Junio C Hamano fb63d7f889 git-add: make the entry stat-clean after re-adding the same contents 
Earlier in commit 0781b8a9b2
(add_file_to_index: skip rehashing if the cached stat already
matches), add_file_to_index() were taught not to re-add the path
if it already matches the index.

The change meant well, but was not executed quite right.  It
used ie_modified() to see if the file on the work tree is really
different from the index, and skipped adding the contents if the
function says "not modified".

This was wrong.  There are three possible comparison results
between the index and the file in the work tree:

 - with lstat(2) we _know_ they are different.  E.g. if the
   length or the owner in the cached stat information is
   different from the length we just obtained from lstat(2), we
   can tell the file is modified without looking at the actual
   contents.

 - with lstat(2) we _know_ they are the same.  The same length,
   the same owner, the same everything (but this has a twist, as
   described below).

 - we cannot tell from lstat(2) information alone and need to go
   to the filesystem to actually compare.

The last case arises from what we call 'racy git' situation,
that can be caused with this sequence:

    $ echo hello >file
    $ git add file
    $ echo aeiou >file ;# the same length

If the second "echo" is done within the same filesystem
timestamp granularity as the first "echo", then the timestamp
recorded by "git add" and the timestamp we get from lstat(2)
will be the same, and we can mistakenly say the file is not
modified.  The path is called 'racily clean'.  We need to
reliably detect racily clean paths are in fact modified.

To solve this problem, when we write out the index, we mark the
index entry that has the same timestamp as the index file itself
(that is the time from the point of view of the filesystem) to
tell any later code that does the lstat(2) comparison not to
trust the cached stat info, and ie_modified() then actually goes
to the filesystem to compare the contents for such a path.

That's all good, but it should not be used for this "git add"
optimization, as the goal of "git add" is to actually update the
path in the index and make it stat-clean.  With the false
optimization, we did _not_ cause any data loss (after all, what
we failed to do was only to update the cached stat information),
but it made the following sequence leave the file stat dirty:

    $ echo hello >file
    $ git add file
    $ echo hello >file ;# the same contents
    $ git add file

The solution is not to use ie_modified() which goes to the
filesystem to see if it is really clean, but instead use
ie_match_stat() with "assume racily clean paths are dirty"
option, to force re-adding of such a path.

There was another problem with "git add -u".  The codepath
shares the same issue when adding the paths that are found to be
modified, but in addition, it asked "git diff-files" machinery
run_diff_files() function (which is "git diff-files") to list
the paths that are modified.  But "git diff-files" machinery
uses the same ie_modified() call so that it does not report
racily clean _and_ actually clean paths as modified, which is
not what we want.

The patch allows the callers of run_diff_files() to pass the
same "assume racily clean paths are dirty" option, and makes
"git-add -u" codepath to use that option, to discover and re-add
racily clean _and_ actually clean paths.

We could further optimize on top of this patch to differentiate
the case where the path really needs re-adding (i.e. the content
of the racily clean entry was indeed different) and the case
where only the cached stat information needs to be refreshed
(i.e. the racily clean entry was actually clean), but I do not
think it is worth it.

This patch applies to maint and all the way up.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-11-10 00:37:39 -08:00

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/*
* Copyright (C) 2005 Junio C Hamano
*/
#ifndef DIFF_H
#define DIFF_H
#include "tree-walk.h"
struct rev_info;
struct diff_options;
struct diff_queue_struct;
typedef void (*change_fn_t)(struct diff_options *options,
unsigned old_mode, unsigned new_mode,
const unsigned char *old_sha1,
const unsigned char *new_sha1,
const char *base, const char *path);
typedef void (*add_remove_fn_t)(struct diff_options *options,
int addremove, unsigned mode,
const unsigned char *sha1,
const char *base, const char *path);
typedef void (*diff_format_fn_t)(struct diff_queue_struct *q,
struct diff_options *options, void *data);
#define DIFF_FORMAT_RAW 0x0001
#define DIFF_FORMAT_DIFFSTAT 0x0002
#define DIFF_FORMAT_NUMSTAT 0x0004
#define DIFF_FORMAT_SUMMARY 0x0008
#define DIFF_FORMAT_PATCH 0x0010
#define DIFF_FORMAT_SHORTSTAT 0x0020
/* These override all above */
#define DIFF_FORMAT_NAME 0x0100
#define DIFF_FORMAT_NAME_STATUS 0x0200
#define DIFF_FORMAT_CHECKDIFF 0x0400
/* Same as output_format = 0 but we know that -s flag was given
* and we should not give default value to output_format.
*/
#define DIFF_FORMAT_NO_OUTPUT 0x0800
#define DIFF_FORMAT_CALLBACK 0x1000
struct diff_options {
const char *filter;
const char *orderfile;
const char *pickaxe;
const char *single_follow;
unsigned recursive:1,
tree_in_recursive:1,
binary:1,
text:1,
full_index:1,
silent_on_remove:1,
find_copies_harder:1,
follow_renames:1,
color_diff:1,
color_diff_words:1,
has_changes:1,
quiet:1,
no_index:1,
allow_external:1,
exit_with_status:1;
int context;
int break_opt;
int detect_rename;
int skip_stat_unmatch;
int line_termination;
int output_format;
int pickaxe_opts;
int rename_score;
int reverse_diff;
int rename_limit;
int setup;
int abbrev;
const char *msg_sep;
const char *stat_sep;
long xdl_opts;
int stat_width;
int stat_name_width;
/* this is set by diffcore for DIFF_FORMAT_PATCH */
int found_changes;
int nr_paths;
const char **paths;
int *pathlens;
change_fn_t change;
add_remove_fn_t add_remove;
diff_format_fn_t format_callback;
void *format_callback_data;
};
enum color_diff {
DIFF_RESET = 0,
DIFF_PLAIN = 1,
DIFF_METAINFO = 2,
DIFF_FRAGINFO = 3,
DIFF_FILE_OLD = 4,
DIFF_FILE_NEW = 5,
DIFF_COMMIT = 6,
DIFF_WHITESPACE = 7,
};
const char *diff_get_color(int diff_use_color, enum color_diff ix);
extern const char mime_boundary_leader[];
extern void diff_tree_setup_paths(const char **paths, struct diff_options *);
extern void diff_tree_release_paths(struct diff_options *);
extern int diff_tree(struct tree_desc *t1, struct tree_desc *t2,
const char *base, struct diff_options *opt);
extern int diff_tree_sha1(const unsigned char *old, const unsigned char *new,
const char *base, struct diff_options *opt);
extern int diff_root_tree_sha1(const unsigned char *new, const char *base,
struct diff_options *opt);
struct combine_diff_path {
struct combine_diff_path *next;
int len;
char *path;
unsigned int mode;
unsigned char sha1[20];
struct combine_diff_parent {
char status;
unsigned int mode;
unsigned char sha1[20];
} parent[FLEX_ARRAY];
};
#define combine_diff_path_size(n, l) \
(sizeof(struct combine_diff_path) + \
sizeof(struct combine_diff_parent) * (n) + (l) + 1)
extern void show_combined_diff(struct combine_diff_path *elem, int num_parent,
int dense, struct rev_info *);
extern void diff_tree_combined(const unsigned char *sha1, const unsigned char parent[][20], int num_parent, int dense, struct rev_info *rev);
extern void diff_tree_combined_merge(const unsigned char *sha1, int, struct rev_info *);
extern void diff_addremove(struct diff_options *,
int addremove,
unsigned mode,
const unsigned char *sha1,
const char *base,
const char *path);
extern void diff_change(struct diff_options *,
unsigned mode1, unsigned mode2,
const unsigned char *sha1,
const unsigned char *sha2,
const char *base, const char *path);
extern void diff_unmerge(struct diff_options *,
const char *path,
unsigned mode,
const unsigned char *sha1);
#define DIFF_SETUP_REVERSE 1
#define DIFF_SETUP_USE_CACHE 2
#define DIFF_SETUP_USE_SIZE_CACHE 4
extern int git_diff_ui_config(const char *var, const char *value);
extern void diff_setup(struct diff_options *);
extern int diff_opt_parse(struct diff_options *, const char **, int);
extern int diff_setup_done(struct diff_options *);
#define DIFF_DETECT_RENAME 1
#define DIFF_DETECT_COPY 2
#define DIFF_PICKAXE_ALL 1
#define DIFF_PICKAXE_REGEX 2
extern void diffcore_std(struct diff_options *);
#define COMMON_DIFF_OPTIONS_HELP \
"\ncommon diff options:\n" \
" -z output diff-raw with lines terminated with NUL.\n" \
" -p output patch format.\n" \
" -u synonym for -p.\n" \
" --patch-with-raw\n" \
" output both a patch and the diff-raw format.\n" \
" --stat show diffstat instead of patch.\n" \
" --numstat show numeric diffstat instead of patch.\n" \
" --patch-with-stat\n" \
" output a patch and prepend its diffstat.\n" \
" --name-only show only names of changed files.\n" \
" --name-status show names and status of changed files.\n" \
" --full-index show full object name on index lines.\n" \
" --abbrev=<n> abbreviate object names in diff-tree header and diff-raw.\n" \
" -R swap input file pairs.\n" \
" -B detect complete rewrites.\n" \
" -M detect renames.\n" \
" -C detect copies.\n" \
" --find-copies-harder\n" \
" try unchanged files as candidate for copy detection.\n" \
" -l<n> limit rename attempts up to <n> paths.\n" \
" -O<file> reorder diffs according to the <file>.\n" \
" -S<string> find filepair whose only one side contains the string.\n" \
" --pickaxe-all\n" \
" show all files diff when -S is used and hit is found.\n" \
" -a --text treat all files as text.\n"
extern int diff_queue_is_empty(void);
extern void diff_flush(struct diff_options*);
/* diff-raw status letters */
#define DIFF_STATUS_ADDED 'A'
#define DIFF_STATUS_COPIED 'C'
#define DIFF_STATUS_DELETED 'D'
#define DIFF_STATUS_MODIFIED 'M'
#define DIFF_STATUS_RENAMED 'R'
#define DIFF_STATUS_TYPE_CHANGED 'T'
#define DIFF_STATUS_UNKNOWN 'X'
#define DIFF_STATUS_UNMERGED 'U'
/* these are not diff-raw status letters proper, but used by
* diffcore-filter insn to specify additional restrictions.
*/
#define DIFF_STATUS_FILTER_AON '*'
#define DIFF_STATUS_FILTER_BROKEN 'B'
extern const char *diff_unique_abbrev(const unsigned char *, int);
/* do not report anything on removed paths */
#define DIFF_SILENT_ON_REMOVED 01
/* report racily-clean paths as modified */
#define DIFF_RACY_IS_MODIFIED 02
extern int run_diff_files(struct rev_info *revs, unsigned int option);
extern int setup_diff_no_index(struct rev_info *revs,
int argc, const char ** argv, int nongit, const char *prefix);
extern int run_diff_files_cmd(struct rev_info *revs, int argc, const char **argv);
extern int run_diff_index(struct rev_info *revs, int cached);
extern int do_diff_cache(const unsigned char *, struct diff_options *);
extern int diff_flush_patch_id(struct diff_options *, unsigned char *);
#endif /* DIFF_H */
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