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.

The default is unlimited.

--big-file-threshold=<n>::

Maximum size of a blob that fast-import will attempt to

create a delta for, expressed in bytes. The default is 512m

(512 MiB). Some importers may wish to lower this on systems

with constrained memory.

--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.

--relative-marks::

After specifying --relative-marks= the paths specified

with --import-marks= and --export-marks= are relative

to an internal directory in the current repository.

In git-fast-import this means that the paths are relative

to the .git/info/fast-import directory. However, other

importers may use a different location.

--no-relative-marks::

Negates a previous --relative-marks. Allows for combining

relative and non-relative marks by interweaving

--(no-)-relative-marks= with the --(import|export)-marks=

options.

--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 it's 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 it's 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.

`feature`::

Require that fast-import supports the specified feature, or

abort if it does not.

`option`::

Specify any of the options listed under OPTIONS that do not

change stream semantic to suit the frontend's needs. 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 | notemodify)*

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`,

`filedeleteall` and `notemodify` 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`, `filerename` and `notemodify` 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, it's 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:gitrevisions[7] 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 usually `<dataref>` must 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. If `<mode>` is `040000`` then

`<dataref>` must be the full 40-byte SHA-1 of an existing

Git tree object or a mark reference set with `--import-marks`.

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.

* `040000`: A subdirectory. Subdirectories can only be specified by

SHA or through a tree mark set with `--import-marks`.

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"`.

Additionally, in `040000` mode, `<path>` may also be an empty string

(`""`) to specify the root of the tree.

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.

`notemodify`

^^^^^^^^^^^^

Included in a `commit` command to add a new note (annotating a given

commit) or change the content of an existing note. This command has

two different means of specifying the content of the note.

External data format::

The data content for the note was already supplied by a prior

`blob` command. The frontend just needs to connect it to the

commit that is to be annotated.

+

....

'N' SP <dataref> SP <committish> 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 note has not been supplied yet.

The frontend wants to supply it as part of this modify

command.

+

....

'N' SP 'inline' SP <committish> LF

data

....

+

See below for a detailed description of the `data` command.

In both formats `<committish>` is any of the commit specification

expressions also accepted by `from` (see above).

`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 it's 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.

`feature`

~~~~~~~~~

Require that fast-import supports the specified feature, or abort if

it does not.

....

'feature' SP <feature> LF

....

The <feature> part of the command may be any string matching

^[a-zA-Z][a-zA-Z-]*$ and should be understood by fast-import.

Feature work identical as their option counterparts with the

exception of the import-marks feature, see below.

The following features are currently supported:

* date-format

* import-marks

* export-marks

* relative-marks

* no-relative-marks

* force

The import-marks behaves differently from when it is specified as

commandline option in that only one "feature import-marks" is allowed

per stream. Also, any --import-marks= specified on the commandline

will override those from the stream (if any).

`option`

~~~~~~~~

Processes the specified option so that git fast-import behaves in a

way that suits the frontend's needs.

Note that options specified by the frontend are overridden by any

options the user may specify to git fast-import itself.

....

'option' SP <option> LF

....

The `<option>` part of the command may contain any of the options

listed in the OPTIONS section that do not change import semantics,

without the leading '--' and is treated in the same way.

Option commands must be the first commands on the input (not counting

feature commands), to give an option command after any non-option

command is an error.

The following commandline options change import semantics and may therefore

not be passed as option:

* date-format

* import-marks

* export-marks

* force

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