This repository has been archived by the owner on Nov 9, 2017. It is now read-only.
forked from git-for-windows/git
/
git-fast-import.txt
1125 lines (943 loc) · 43.3 KB
/
git-fast-import.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
git-fast-import(1)
==================
NAME
----
git-fast-import - Backend for fast Git data importers
SYNOPSIS
--------
frontend | 'git fast-import' [options]
DESCRIPTION
-----------
This program is usually not what the end user wants to run directly.
Most end users want to use one of the existing frontend programs,
which parses a specific type of foreign source and feeds the contents
stored there to 'git-fast-import'.
fast-import reads a mixed command/data stream from standard input and
writes one or more packfiles directly into the current repository.
When EOF is received on standard input, fast import writes out
updated branch and tag refs, fully updating the current repository
with the newly imported data.
The fast-import backend itself can import into an empty repository (one that
has already been initialized by 'git-init') or incrementally
update an existing populated repository. Whether or not incremental
imports are supported from a particular foreign source depends on
the frontend program in use.
OPTIONS
-------
--date-format=<fmt>::
Specify the type of dates the frontend will supply to
fast-import within `author`, `committer` and `tagger` commands.
See ``Date Formats'' below for details about which formats
are supported, and their syntax.
--force::
Force updating modified existing branches, even if doing
so would cause commits to be lost (as the new commit does
not contain the old commit).
--max-pack-size=<n>::
Maximum size of each output packfile, expressed in MiB.
The default is 4096 (4 GiB) as that is the maximum allowed
packfile size (due to file format limitations). Some
importers may wish to lower this, such as to ensure the
resulting packfiles fit on CDs.
--depth=<n>::
Maximum delta depth, for blob and tree deltification.
Default is 10.
--active-branches=<n>::
Maximum number of branches to maintain active at once.
See ``Memory Utilization'' below for details. Default is 5.
--export-marks=<file>::
Dumps the internal marks table to <file> when complete.
Marks are written one per line as `:markid SHA-1`.
Frontends can use this file to validate imports after they
have been completed, or to save the marks table across
incremental runs. As <file> is only opened and truncated
at checkpoint (or completion) the same path can also be
safely given to \--import-marks.
--import-marks=<file>::
Before processing any input, load the marks specified in
<file>. The input file must exist, must be readable, and
must use the same format as produced by \--export-marks.
Multiple options may be supplied to import more than one
set of marks. If a mark is defined to different values,
the last file wins.
--export-pack-edges=<file>::
After creating a packfile, print a line of data to
<file> listing the filename of the packfile and the last
commit on each branch that was written to that packfile.
This information may be useful after importing projects
whose total object set exceeds the 4 GiB packfile limit,
as these commits can be used as edge points during calls
to 'git-pack-objects'.
--quiet::
Disable all non-fatal output, making fast-import silent when it
is successful. This option disables the output shown by
\--stats.
--stats::
Display some basic statistics about the objects fast-import has
created, the packfiles they were stored into, and the
memory used by fast-import during this run. Showing this output
is currently the default, but can be disabled with \--quiet.
Performance
-----------
The design of fast-import allows it to import large projects in a minimum
amount of memory usage and processing time. Assuming the frontend
is able to keep up with fast-import and feed it a constant stream of data,
import times for projects holding 10+ years of history and containing
100,000+ individual commits are generally completed in just 1-2
hours on quite modest (~$2,000 USD) hardware.
Most bottlenecks appear to be in foreign source data access (the
source just cannot extract revisions fast enough) or disk IO (fast-import
writes as fast as the disk will take the data). Imports will run
faster if the source data is stored on a different drive than the
destination Git repository (due to less IO contention).
Development Cost
----------------
A typical frontend for fast-import tends to weigh in at approximately 200
lines of Perl/Python/Ruby code. Most developers have been able to
create working importers in just a couple of hours, even though it
is their first exposure to fast-import, and sometimes even to Git. This is
an ideal situation, given that most conversion tools are throw-away
(use once, and never look back).
Parallel Operation
------------------
Like 'git-push' or 'git-fetch', imports handled by fast-import are safe to
run alongside parallel `git repack -a -d` or `git gc` invocations,
or any other Git operation (including 'git-prune', as loose objects
are never used by fast-import).
fast-import does not lock the branch or tag refs it is actively importing.
After the import, during its ref update phase, fast-import tests each
existing branch ref to verify the update will be a fast-forward
update (the commit stored in the ref is contained in the new
history of the commit to be written). If the update is not a
fast-forward update, fast-import will skip updating that ref and instead
prints a warning message. fast-import will always attempt to update all
branch refs, and does not stop on the first failure.
Branch updates can be forced with \--force, but its recommended that
this only be used on an otherwise quiet repository. Using \--force
is not necessary for an initial import into an empty repository.
Technical Discussion
--------------------
fast-import tracks a set of branches in memory. Any branch can be created
or modified at any point during the import process by sending a
`commit` command on the input stream. This design allows a frontend
program to process an unlimited number of branches simultaneously,
generating commits in the order they are available from the source
data. It also simplifies the frontend programs considerably.
fast-import does not use or alter the current working directory, or any
file within it. (It does however update the current Git repository,
as referenced by `GIT_DIR`.) Therefore an import frontend may use
the working directory for its own purposes, such as extracting file
revisions from the foreign source. This ignorance of the working
directory also allows fast-import to run very quickly, as it does not
need to perform any costly file update operations when switching
between branches.
Input Format
------------
With the exception of raw file data (which Git does not interpret)
the fast-import input format is text (ASCII) based. This text based
format simplifies development and debugging of frontend programs,
especially when a higher level language such as Perl, Python or
Ruby is being used.
fast-import is very strict about its input. Where we say SP below we mean
*exactly* one space. Likewise LF means one (and only one) linefeed.
Supplying additional whitespace characters will cause unexpected
results, such as branch names or file names with leading or trailing
spaces in their name, or early termination of fast-import when it encounters
unexpected input.
Stream Comments
~~~~~~~~~~~~~~~
To aid in debugging frontends fast-import ignores any line that
begins with `#` (ASCII pound/hash) up to and including the line
ending `LF`. A comment line may contain any sequence of bytes
that does not contain an LF and therefore may be used to include
any detailed debugging information that might be specific to the
frontend and useful when inspecting a fast-import data stream.
Date Formats
~~~~~~~~~~~~
The following date formats are supported. A frontend should select
the format it will use for this import by passing the format name
in the \--date-format=<fmt> command line option.
`raw`::
This is the Git native format and is `<time> SP <offutc>`.
It is also fast-import's default format, if \--date-format was
not specified.
+
The time of the event is specified by `<time>` as the number of
seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is
written as an ASCII decimal integer.
+
The local offset is specified by `<offutc>` as a positive or negative
offset from UTC. For example EST (which is 5 hours behind UTC)
would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''.
The local offset does not affect `<time>`; it is used only as an
advisement to help formatting routines display the timestamp.
+
If the local offset is not available in the source material, use
``+0000'', or the most common local offset. For example many
organizations have a CVS repository which has only ever been accessed
by users who are located in the same location and timezone. In this
case a reasonable offset from UTC could be assumed.
+
Unlike the `rfc2822` format, this format is very strict. Any
variation in formatting will cause fast-import to reject the value.
`rfc2822`::
This is the standard email format as described by RFC 2822.
+
An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git
parser is accurate, but a little on the lenient side. It is the
same parser used by 'git-am' when applying patches
received from email.
+
Some malformed strings may be accepted as valid dates. In some of
these cases Git will still be able to obtain the correct date from
the malformed string. There are also some types of malformed
strings which Git will parse wrong, and yet consider valid.
Seriously malformed strings will be rejected.
+
Unlike the `raw` format above, the timezone/UTC offset information
contained in an RFC 2822 date string is used to adjust the date
value to UTC prior to storage. Therefore it is important that
this information be as accurate as possible.
+
If the source material uses RFC 2822 style dates,
the frontend should let fast-import handle the parsing and conversion
(rather than attempting to do it itself) as the Git parser has
been well tested in the wild.
+
Frontends should prefer the `raw` format if the source material
already uses UNIX-epoch format, can be coaxed to give dates in that
format, or its format is easily convertible to it, as there is no
ambiguity in parsing.
`now`::
Always use the current time and timezone. The literal
`now` must always be supplied for `<when>`.
+
This is a toy format. The current time and timezone of this system
is always copied into the identity string at the time it is being
created by fast-import. There is no way to specify a different time or
timezone.
+
This particular format is supplied as its short to implement and
may be useful to a process that wants to create a new commit
right now, without needing to use a working directory or
'git-update-index'.
+
If separate `author` and `committer` commands are used in a `commit`
the timestamps may not match, as the system clock will be polled
twice (once for each command). The only way to ensure that both
author and committer identity information has the same timestamp
is to omit `author` (thus copying from `committer`) or to use a
date format other than `now`.
Commands
~~~~~~~~
fast-import accepts several commands to update the current repository
and control the current import process. More detailed discussion
(with examples) of each command follows later.
`commit`::
Creates a new branch or updates an existing branch by
creating a new commit and updating the branch to point at
the newly created commit.
`tag`::
Creates an annotated tag object from an existing commit or
branch. Lightweight tags are not supported by this command,
as they are not recommended for recording meaningful points
in time.
`reset`::
Reset an existing branch (or a new branch) to a specific
revision. This command must be used to change a branch to
a specific revision without making a commit on it.
`blob`::
Convert raw file data into a blob, for future use in a
`commit` command. This command is optional and is not
needed to perform an import.
`checkpoint`::
Forces fast-import to close the current packfile, generate its
unique SHA-1 checksum and index, and start a new packfile.
This command is optional and is not needed to perform
an import.
`progress`::
Causes fast-import to echo the entire line to its own
standard output. This command is optional and is not needed
to perform an import.
`commit`
~~~~~~~~
Create or update a branch with a new commit, recording one logical
change to the project.
....
'commit' SP <ref> LF
mark?
('author' SP <name> SP LT <email> GT SP <when> LF)?
'committer' SP <name> SP LT <email> GT SP <when> LF
data
('from' SP <committish> LF)?
('merge' SP <committish> LF)?
(filemodify | filedelete | filecopy | filerename | filedeleteall)*
LF?
....
where `<ref>` is the name of the branch to make the commit on.
Typically branch names are prefixed with `refs/heads/` in
Git, so importing the CVS branch symbol `RELENG-1_0` would use
`refs/heads/RELENG-1_0` for the value of `<ref>`. The value of
`<ref>` must be a valid refname in Git. As `LF` is not valid in
a Git refname, no quoting or escaping syntax is supported here.
A `mark` command may optionally appear, requesting fast-import to save a
reference to the newly created commit for future use by the frontend
(see below for format). It is very common for frontends to mark
every commit they create, thereby allowing future branch creation
from any imported commit.
The `data` command following `committer` must supply the commit
message (see below for `data` command syntax). To import an empty
commit message use a 0 length data. Commit messages are free-form
and are not interpreted by Git. Currently they must be encoded in
UTF-8, as fast-import does not permit other encodings to be specified.
Zero or more `filemodify`, `filedelete`, `filecopy`, `filerename`
and `filedeleteall` commands
may be included to update the contents of the branch prior to
creating the commit. These commands may be supplied in any order.
However it is recommended that a `filedeleteall` command precede
all `filemodify`, `filecopy` and `filerename` commands in the same
commit, as `filedeleteall`
wipes the branch clean (see below).
The `LF` after the command is optional (it used to be required).
`author`
^^^^^^^^
An `author` command may optionally appear, if the author information
might differ from the committer information. If `author` is omitted
then fast-import will automatically use the committer's information for
the author portion of the commit. See below for a description of
the fields in `author`, as they are identical to `committer`.
`committer`
^^^^^^^^^^^
The `committer` command indicates who made this commit, and when
they made it.
Here `<name>` is the person's display name (for example
``Com M Itter'') and `<email>` is the person's email address
(``cm@example.com''). `LT` and `GT` are the literal less-than (\x3c)
and greater-than (\x3e) symbols. These are required to delimit
the email address from the other fields in the line. Note that
`<name>` is free-form and may contain any sequence of bytes, except
`LT` and `LF`. It is typically UTF-8 encoded.
The time of the change is specified by `<when>` using the date format
that was selected by the \--date-format=<fmt> command line option.
See ``Date Formats'' above for the set of supported formats, and
their syntax.
`from`
^^^^^^
The `from` command is used to specify the commit to initialize
this branch from. This revision will be the first ancestor of the
new commit.
Omitting the `from` command in the first commit of a new branch
will cause fast-import to create that commit with no ancestor. This
tends to be desired only for the initial commit of a project.
If the frontend creates all files from scratch when making a new
branch, a `merge` command may be used instead of `from` to start
the commit with an empty tree.
Omitting the `from` command on existing branches is usually desired,
as the current commit on that branch is automatically assumed to
be the first ancestor of the new commit.
As `LF` is not valid in a Git refname or SHA-1 expression, no
quoting or escaping syntax is supported within `<committish>`.
Here `<committish>` is any of the following:
* The name of an existing branch already in fast-import's internal branch
table. If fast-import doesn't know the name, its treated as a SHA-1
expression.
* A mark reference, `:<idnum>`, where `<idnum>` is the mark number.
+
The reason fast-import uses `:` to denote a mark reference is this character
is not legal in a Git branch name. The leading `:` makes it easy
to distinguish between the mark 42 (`:42`) and the branch 42 (`42`
or `refs/heads/42`), or an abbreviated SHA-1 which happened to
consist only of base-10 digits.
+
Marks must be declared (via `mark`) before they can be used.
* A complete 40 byte or abbreviated commit SHA-1 in hex.
* Any valid Git SHA-1 expression that resolves to a commit. See
``SPECIFYING REVISIONS'' in linkgit:git-rev-parse[1] for details.
The special case of restarting an incremental import from the
current branch value should be written as:
----
from refs/heads/branch^0
----
The `{caret}0` suffix is necessary as fast-import does not permit a branch to
start from itself, and the branch is created in memory before the
`from` command is even read from the input. Adding `{caret}0` will force
fast-import to resolve the commit through Git's revision parsing library,
rather than its internal branch table, thereby loading in the
existing value of the branch.
`merge`
^^^^^^^
Includes one additional ancestor commit. If the `from` command is
omitted when creating a new branch, the first `merge` commit will be
the first ancestor of the current commit, and the branch will start
out with no files. An unlimited number of `merge` commands per
commit are permitted by fast-import, thereby establishing an n-way merge.
However Git's other tools never create commits with more than 15
additional ancestors (forming a 16-way merge). For this reason
it is suggested that frontends do not use more than 15 `merge`
commands per commit; 16, if starting a new, empty branch.
Here `<committish>` is any of the commit specification expressions
also accepted by `from` (see above).
`filemodify`
^^^^^^^^^^^^
Included in a `commit` command to add a new file or change the
content of an existing file. This command has two different means
of specifying the content of the file.
External data format::
The data content for the file was already supplied by a prior
`blob` command. The frontend just needs to connect it.
+
....
'M' SP <mode> SP <dataref> SP <path> LF
....
+
Here `<dataref>` can be either a mark reference (`:<idnum>`)
set by a prior `blob` command, or a full 40-byte SHA-1 of an
existing Git blob object.
Inline data format::
The data content for the file has not been supplied yet.
The frontend wants to supply it as part of this modify
command.
+
....
'M' SP <mode> SP 'inline' SP <path> LF
data
....
+
See below for a detailed description of the `data` command.
In both formats `<mode>` is the type of file entry, specified
in octal. Git only supports the following modes:
* `100644` or `644`: A normal (not-executable) file. The majority
of files in most projects use this mode. If in doubt, this is
what you want.
* `100755` or `755`: A normal, but executable, file.
* `120000`: A symlink, the content of the file will be the link target.
* `160000`: A gitlink, SHA-1 of the object refers to a commit in
another repository. Git links can only be specified by SHA or through
a commit mark. They are used to implement submodules.
In both formats `<path>` is the complete path of the file to be added
(if not already existing) or modified (if already existing).
A `<path>` string must use UNIX-style directory separators (forward
slash `/`), may contain any byte other than `LF`, and must not
start with double quote (`"`).
If an `LF` or double quote must be encoded into `<path>` shell-style
quoting should be used, e.g. `"path/with\n and \" in it"`.
The value of `<path>` must be in canonical form. That is it must not:
* contain an empty directory component (e.g. `foo//bar` is invalid),
* end with a directory separator (e.g. `foo/` is invalid),
* start with a directory separator (e.g. `/foo` is invalid),
* contain the special component `.` or `..` (e.g. `foo/./bar` and
`foo/../bar` are invalid).
It is recommended that `<path>` always be encoded using UTF-8.
`filedelete`
^^^^^^^^^^^^
Included in a `commit` command to remove a file or recursively
delete an entire directory from the branch. If the file or directory
removal makes its parent directory empty, the parent directory will
be automatically removed too. This cascades up the tree until the
first non-empty directory or the root is reached.
....
'D' SP <path> LF
....
here `<path>` is the complete path of the file or subdirectory to
be removed from the branch.
See `filemodify` above for a detailed description of `<path>`.
`filecopy`
^^^^^^^^^^^^
Recursively copies an existing file or subdirectory to a different
location within the branch. The existing file or directory must
exist. If the destination exists it will be completely replaced
by the content copied from the source.
....
'C' SP <path> SP <path> LF
....
here the first `<path>` is the source location and the second
`<path>` is the destination. See `filemodify` above for a detailed
description of what `<path>` may look like. To use a source path
that contains SP the path must be quoted.
A `filecopy` command takes effect immediately. Once the source
location has been copied to the destination any future commands
applied to the source location will not impact the destination of
the copy.
`filerename`
^^^^^^^^^^^^
Renames an existing file or subdirectory to a different location
within the branch. The existing file or directory must exist. If
the destination exists it will be replaced by the source directory.
....
'R' SP <path> SP <path> LF
....
here the first `<path>` is the source location and the second
`<path>` is the destination. See `filemodify` above for a detailed
description of what `<path>` may look like. To use a source path
that contains SP the path must be quoted.
A `filerename` command takes effect immediately. Once the source
location has been renamed to the destination any future commands
applied to the source location will create new files there and not
impact the destination of the rename.
Note that a `filerename` is the same as a `filecopy` followed by a
`filedelete` of the source location. There is a slight performance
advantage to using `filerename`, but the advantage is so small
that it is never worth trying to convert a delete/add pair in
source material into a rename for fast-import. This `filerename`
command is provided just to simplify frontends that already have
rename information and don't want bother with decomposing it into a
`filecopy` followed by a `filedelete`.
`filedeleteall`
^^^^^^^^^^^^^^^
Included in a `commit` command to remove all files (and also all
directories) from the branch. This command resets the internal
branch structure to have no files in it, allowing the frontend
to subsequently add all interesting files from scratch.
....
'deleteall' LF
....
This command is extremely useful if the frontend does not know
(or does not care to know) what files are currently on the branch,
and therefore cannot generate the proper `filedelete` commands to
update the content.
Issuing a `filedeleteall` followed by the needed `filemodify`
commands to set the correct content will produce the same results
as sending only the needed `filemodify` and `filedelete` commands.
The `filedeleteall` approach may however require fast-import to use slightly
more memory per active branch (less than 1 MiB for even most large
projects); so frontends that can easily obtain only the affected
paths for a commit are encouraged to do so.
`mark`
~~~~~~
Arranges for fast-import to save a reference to the current object, allowing
the frontend to recall this object at a future point in time, without
knowing its SHA-1. Here the current object is the object creation
command the `mark` command appears within. This can be `commit`,
`tag`, and `blob`, but `commit` is the most common usage.
....
'mark' SP ':' <idnum> LF
....
where `<idnum>` is the number assigned by the frontend to this mark.
The value of `<idnum>` is expressed as an ASCII decimal integer.
The value 0 is reserved and cannot be used as
a mark. Only values greater than or equal to 1 may be used as marks.
New marks are created automatically. Existing marks can be moved
to another object simply by reusing the same `<idnum>` in another
`mark` command.
`tag`
~~~~~
Creates an annotated tag referring to a specific commit. To create
lightweight (non-annotated) tags see the `reset` command below.
....
'tag' SP <name> LF
'from' SP <committish> LF
'tagger' SP <name> SP LT <email> GT SP <when> LF
data
....
where `<name>` is the name of the tag to create.
Tag names are automatically prefixed with `refs/tags/` when stored
in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would
use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the
corresponding ref as `refs/tags/RELENG-1_0-FINAL`.
The value of `<name>` must be a valid refname in Git and therefore
may contain forward slashes. As `LF` is not valid in a Git refname,
no quoting or escaping syntax is supported here.
The `from` command is the same as in the `commit` command; see
above for details.
The `tagger` command uses the same format as `committer` within
`commit`; again see above for details.
The `data` command following `tagger` must supply the annotated tag
message (see below for `data` command syntax). To import an empty
tag message use a 0 length data. Tag messages are free-form and are
not interpreted by Git. Currently they must be encoded in UTF-8,
as fast-import does not permit other encodings to be specified.
Signing annotated tags during import from within fast-import is not
supported. Trying to include your own PGP/GPG signature is not
recommended, as the frontend does not (easily) have access to the
complete set of bytes which normally goes into such a signature.
If signing is required, create lightweight tags from within fast-import with
`reset`, then create the annotated versions of those tags offline
with the standard 'git-tag' process.
`reset`
~~~~~~~
Creates (or recreates) the named branch, optionally starting from
a specific revision. The reset command allows a frontend to issue
a new `from` command for an existing branch, or to create a new
branch from an existing commit without creating a new commit.
....
'reset' SP <ref> LF
('from' SP <committish> LF)?
LF?
....
For a detailed description of `<ref>` and `<committish>` see above
under `commit` and `from`.
The `LF` after the command is optional (it used to be required).
The `reset` command can also be used to create lightweight
(non-annotated) tags. For example:
====
reset refs/tags/938
from :938
====
would create the lightweight tag `refs/tags/938` referring to
whatever commit mark `:938` references.
`blob`
~~~~~~
Requests writing one file revision to the packfile. The revision
is not connected to any commit; this connection must be formed in
a subsequent `commit` command by referencing the blob through an
assigned mark.
....
'blob' LF
mark?
data
....
The mark command is optional here as some frontends have chosen
to generate the Git SHA-1 for the blob on their own, and feed that
directly to `commit`. This is typically more work than its worth
however, as marks are inexpensive to store and easy to use.
`data`
~~~~~~
Supplies raw data (for use as blob/file content, commit messages, or
annotated tag messages) to fast-import. Data can be supplied using an exact
byte count or delimited with a terminating line. Real frontends
intended for production-quality conversions should always use the
exact byte count format, as it is more robust and performs better.
The delimited format is intended primarily for testing fast-import.
Comment lines appearing within the `<raw>` part of `data` commands
are always taken to be part of the body of the data and are therefore
never ignored by fast-import. This makes it safe to import any
file/message content whose lines might start with `#`.
Exact byte count format::
The frontend must specify the number of bytes of data.
+
....
'data' SP <count> LF
<raw> LF?
....
+
where `<count>` is the exact number of bytes appearing within
`<raw>`. The value of `<count>` is expressed as an ASCII decimal
integer. The `LF` on either side of `<raw>` is not
included in `<count>` and will not be included in the imported data.
+
The `LF` after `<raw>` is optional (it used to be required) but
recommended. Always including it makes debugging a fast-import
stream easier as the next command always starts in column 0
of the next line, even if `<raw>` did not end with an `LF`.
Delimited format::
A delimiter string is used to mark the end of the data.
fast-import will compute the length by searching for the delimiter.
This format is primarily useful for testing and is not
recommended for real data.
+
....
'data' SP '<<' <delim> LF
<raw> LF
<delim> LF
LF?
....
+
where `<delim>` is the chosen delimiter string. The string `<delim>`
must not appear on a line by itself within `<raw>`, as otherwise
fast-import will think the data ends earlier than it really does. The `LF`
immediately trailing `<raw>` is part of `<raw>`. This is one of
the limitations of the delimited format, it is impossible to supply
a data chunk which does not have an LF as its last byte.
+
The `LF` after `<delim> LF` is optional (it used to be required).
`checkpoint`
~~~~~~~~~~~~
Forces fast-import to close the current packfile, start a new one, and to
save out all current branch refs, tags and marks.
....
'checkpoint' LF
LF?
....
Note that fast-import automatically switches packfiles when the current
packfile reaches \--max-pack-size, or 4 GiB, whichever limit is
smaller. During an automatic packfile switch fast-import does not update
the branch refs, tags or marks.
As a `checkpoint` can require a significant amount of CPU time and
disk IO (to compute the overall pack SHA-1 checksum, generate the
corresponding index file, and update the refs) it can easily take
several minutes for a single `checkpoint` command to complete.
Frontends may choose to issue checkpoints during extremely large
and long running imports, or when they need to allow another Git
process access to a branch. However given that a 30 GiB Subversion
repository can be loaded into Git through fast-import in about 3 hours,
explicit checkpointing may not be necessary.
The `LF` after the command is optional (it used to be required).
`progress`
~~~~~~~~~~
Causes fast-import to print the entire `progress` line unmodified to
its standard output channel (file descriptor 1) when the command is
processed from the input stream. The command otherwise has no impact
on the current import, or on any of fast-import's internal state.
....
'progress' SP <any> LF
LF?
....
The `<any>` part of the command may contain any sequence of bytes
that does not contain `LF`. The `LF` after the command is optional.
Callers may wish to process the output through a tool such as sed to
remove the leading part of the line, for example:
====
frontend | git fast-import | sed 's/^progress //'
====
Placing a `progress` command immediately after a `checkpoint` will
inform the reader when the `checkpoint` has been completed and it
can safely access the refs that fast-import updated.
Crash Reports
-------------
If fast-import is supplied invalid input it will terminate with a
non-zero exit status and create a crash report in the top level of
the Git repository it was importing into. Crash reports contain
a snapshot of the internal fast-import state as well as the most
recent commands that lead up to the crash.
All recent commands (including stream comments, file changes and
progress commands) are shown in the command history within the crash
report, but raw file data and commit messages are excluded from the
crash report. This exclusion saves space within the report file
and reduces the amount of buffering that fast-import must perform
during execution.
After writing a crash report fast-import will close the current
packfile and export the marks table. This allows the frontend
developer to inspect the repository state and resume the import from
the point where it crashed. The modified branches and tags are not
updated during a crash, as the import did not complete successfully.
Branch and tag information can be found in the crash report and
must be applied manually if the update is needed.
An example crash:
====
$ cat >in <<END_OF_INPUT
# my very first test commit
commit refs/heads/master
committer Shawn O. Pearce <spearce> 19283 -0400
# who is that guy anyway?
data <<EOF
this is my commit
EOF
M 644 inline .gitignore
data <<EOF
.gitignore
EOF
M 777 inline bob
END_OF_INPUT
$ git fast-import <in
fatal: Corrupt mode: M 777 inline bob
fast-import: dumping crash report to .git/fast_import_crash_8434
$ cat .git/fast_import_crash_8434
fast-import crash report:
fast-import process: 8434
parent process : 1391
at Sat Sep 1 00:58:12 2007
fatal: Corrupt mode: M 777 inline bob
Most Recent Commands Before Crash
---------------------------------
# my very first test commit
commit refs/heads/master
committer Shawn O. Pearce <spearce> 19283 -0400
# who is that guy anyway?
data <<EOF
M 644 inline .gitignore
data <<EOF
* M 777 inline bob
Active Branch LRU
-----------------
active_branches = 1 cur, 5 max
pos clock name
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1) 0 refs/heads/master
Inactive Branches
-----------------
refs/heads/master:
status : active loaded dirty
tip commit : 0000000000000000000000000000000000000000
old tree : 0000000000000000000000000000000000000000
cur tree : 0000000000000000000000000000000000000000
commit clock: 0
last pack :
-------------------
END OF CRASH REPORT
====
Tips and Tricks
---------------
The following tips and tricks have been collected from various
users of fast-import, and are offered here as suggestions.
Use One Mark Per Commit
~~~~~~~~~~~~~~~~~~~~~~~
When doing a repository conversion, use a unique mark per commit
(`mark :<n>`) and supply the \--export-marks option on the command
line. fast-import will dump a file which lists every mark and the Git
object SHA-1 that corresponds to it. If the frontend can tie
the marks back to the source repository, it is easy to verify the
accuracy and completeness of the import by comparing each Git
commit to the corresponding source revision.
Coming from a system such as Perforce or Subversion this should be
quite simple, as the fast-import mark can also be the Perforce changeset
number or the Subversion revision number.
Freely Skip Around Branches
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Don't bother trying to optimize the frontend to stick to one branch
at a time during an import. Although doing so might be slightly
faster for fast-import, it tends to increase the complexity of the frontend
code considerably.
The branch LRU builtin to fast-import tends to behave very well, and the
cost of activating an inactive branch is so low that bouncing around
between branches has virtually no impact on import performance.
Handling Renames
~~~~~~~~~~~~~~~~
When importing a renamed file or directory, simply delete the old
name(s) and modify the new name(s) during the corresponding commit.
Git performs rename detection after-the-fact, rather than explicitly
during a commit.
Use Tag Fixup Branches
~~~~~~~~~~~~~~~~~~~~~~
Some other SCM systems let the user create a tag from multiple
files which are not from the same commit/changeset. Or to create
tags which are a subset of the files available in the repository.
Importing these tags as-is in Git is impossible without making at
least one commit which ``fixes up'' the files to match the content
of the tag. Use fast-import's `reset` command to reset a dummy branch
outside of your normal branch space to the base commit for the tag,
then commit one or more file fixup commits, and finally tag the
dummy branch.
For example since all normal branches are stored under `refs/heads/`
name the tag fixup branch `TAG_FIXUP`. This way it is impossible for
the fixup branch used by the importer to have namespace conflicts
with real branches imported from the source (the name `TAG_FIXUP`
is not `refs/heads/TAG_FIXUP`).
When committing fixups, consider using `merge` to connect the
commit(s) which are supplying file revisions to the fixup branch.
Doing so will allow tools such as 'git-blame' to track
through the real commit history and properly annotate the source
files.
After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP`
to remove the dummy branch.
Import Now, Repack Later
~~~~~~~~~~~~~~~~~~~~~~~~
As soon as fast-import completes the Git repository is completely valid
and ready for use. Typically this takes only a very short time,
even for considerably large projects (100,000+ commits).
However repacking the repository is necessary to improve data
locality and access performance. It can also take hours on extremely
large projects (especially if -f and a large \--window parameter is
used). Since repacking is safe to run alongside readers and writers,
run the repack in the background and let it finish when it finishes.
There is no reason to wait to explore your new Git project!
If you choose to wait for the repack, don't try to run benchmarks
or performance tests until repacking is completed. fast-import outputs
suboptimal packfiles that are simply never seen in real use
situations.
Repacking Historical Data
~~~~~~~~~~~~~~~~~~~~~~~~~
If you are repacking very old imported data (e.g. older than the
last year), consider expending some extra CPU time and supplying
\--window=50 (or higher) when you run 'git-repack'.
This will take longer, but will also produce a smaller packfile.
You only need to expend the effort once, and everyone using your
project will benefit from the smaller repository.
Include Some Progress Messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Every once in a while have your frontend emit a `progress` message
to fast-import. The contents of the messages are entirely free-form,
so one suggestion would be to output the current month and year
each time the current commit date moves into the next month.