git-fast-import.txt

git-fast-import(1)
==================

NAME
----
git-fast-import - Backend for fast Git data importers


SYNOPSIS
--------
[verse]
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
-------

--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).

--quiet::
	Disable the output shown by --stats, making fast-import usually
	be silent when it is successful.  However, if the import stream
	has directives intended to show user output (e.g. `progress`
	directives), the corresponding messages will still be shown.

--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.

--allow-unsafe-features::
	Many command-line options can be provided as part of the
	fast-import stream itself by using the `feature` or `option`
	commands. However, some of these options are unsafe (e.g.,
	allowing fast-import to access the filesystem outside of the
	repository). These options are disabled by default, but can be
	allowed by providing this option on the command line.  This
	currently impacts only the `export-marks`, `import-marks`, and
	`import-marks-if-exists` feature commands.
+
	Only enable this option if you trust the program generating the
	fast-import stream! This option is enabled automatically for
	remote-helpers that use the `import` capability, as they are
	already trusted to run their own code.

Options for Frontends
~~~~~~~~~~~~~~~~~~~~~

--cat-blob-fd=<fd>::
	Write responses to `get-mark`, `cat-blob`, and `ls` queries to the
	file descriptor <fd> instead of `stdout`.  Allows `progress`
	output intended for the end-user to be separated from other
	output.

--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.

--done::
	Terminate with error if there is no `done` command at the end of
	the stream.  This option might be useful for detecting errors
	that cause the frontend to terminate before it has started to
	write a stream.

Locations of Marks Files
~~~~~~~~~~~~~~~~~~~~~~~~

--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.

--import-marks-if-exists=<file>::
	Like --import-marks but instead of erroring out, silently
	skips the file if it does not exist.

--[no-]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.
+
Relative and non-relative marks may be combined by interweaving
--(no-)-relative-marks with the --(import|export)-marks= options.

Submodule Rewriting
~~~~~~~~~~~~~~~~~~~

--rewrite-submodules-from=<name>:<file>::
--rewrite-submodules-to=<name>:<file>::
  Rewrite the object IDs for the submodule specified by <name> from the values
	used in the from <file> to those used in the to <file>. The from marks should
	have been created by `git fast-export`, and the to marks should have been
	created by `git fast-import` when importing that same submodule.
+
<name> may be any arbitrary string not containing a colon character, but the
same value must be used with both options when specifying corresponding marks.
Multiple submodules may be specified with different values for <name>. It is an
error not to use these options in corresponding pairs.
+
These options are primarily useful when converting a repository from one hash
algorithm to another; without them, fast-import will fail if it encounters a
submodule because it has no way of writing the object ID into the new hash
algorithm.

Performance and Compression Tuning
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--active-branches=<n>::
	Maximum number of branches to maintain active at once.
	See ``Memory Utilization'' below for details.  Default is 5.

--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 50.

--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'.

--max-pack-size=<n>::
	Maximum size of each output packfile.
	The default is unlimited.

fastimport.unpackLimit::
	See linkgit:git-config[1]

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
and HT one (and only one) horizontal tab.
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 time zone.  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,
and some sanity checks on the numeric values may also be performed.

`raw-permissive`::
	This is the same as `raw` except that no sanity checks on
	the numeric epoch and local offset are performed.  This can
	be useful when trying to filter or import an existing history
	with e.g. bogus timezone values.

`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 time zone/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 time zone.  The literal
	`now` must always be supplied for `<when>`.
+
This is a toy format.  The current time and time zone 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
time zone.
+
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.

`alias`::
	Record that a mark refers to a given object without first
	creating any new object.  Using --import-marks and referring
	to missing marks will cause fast-import to fail, so aliases
	can provide a way to set otherwise pruned commits to a valid
	value (e.g. the nearest non-pruned ancestor).

`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.

`done`::
	Marks the end of the stream. This command is optional
	unless the `done` feature was requested using the
	`--done` command-line option or `feature done` command.

`get-mark`::
	Causes fast-import to print the SHA-1 corresponding to a mark
	to the file descriptor set with `--cat-blob-fd`, or `stdout` if
	unspecified.

`cat-blob`::
	Causes fast-import to print a blob in 'cat-file --batch'
	format to the file descriptor set with `--cat-blob-fd` or
	`stdout` if unspecified.

`ls`::
	Causes fast-import to print a line describing a directory
	entry in 'ls-tree' format to the file descriptor set with
	`--cat-blob-fd` or `stdout` if unspecified.

`feature`::
	Enable the specified feature. This requires that fast-import
	supports the specified feature, and aborts 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?
	original-oid?
	('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
	'committer' (SP <name>)? SP LT <email> GT SP <when> LF
	('encoding' SP <encoding>)?
	data
	('from' SP <commit-ish> LF)?
	('merge' SP <commit-ish> 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).  Note
that for reasons of backward compatibility, if the commit ends with a
`data` command (i.e. it has no `from`, `merge`, `filemodify`,
`filedelete`, `filecopy`, `filerename`, `filedeleteall` or
`notemodify` commands) then two `LF` commands may appear at the end of
the command instead of just one.

`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>` and `<email>` are free-form and may contain any sequence
of bytes, except `LT`, `GT` and `LF`.  `<name>` 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.

`encoding`
^^^^^^^^^^
The optional `encoding` command indicates the encoding of the commit
message.  Most commits are UTF-8 and the encoding is omitted, but this
allows importing commit messages into git without first reencoding them.

`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.  The state of the tree built at this commit will begin
with the state at the `from` commit, and be altered by the content
modifications in this 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 `<commit-ish>`.

Here `<commit-ish>` 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 null SHA-1 (40 zeros) specifies that the branch is to be
  removed.

The special case of restarting an incremental import from the
current branch value should be written as:
----
	from refs/heads/branch^0
----
The `^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 `^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.  The additional ancestry
link does not change the way the tree state is built at this 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.

Here `<commit-ish>` 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 (`"`).

A path can use C-style string quoting; this is accepted in all cases
and mandatory if the filename starts with double quote or contains
`LF`. In C-style quoting, the complete name should be surrounded with
double quotes, and any `LF`, backslash, or double quote characters
must be escaped by preceding them with a backslash (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).

The root of the tree can be represented by an empty string as `<path>`.

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` `<notes_ref>` command to add a new note
annotating a `<commit-ish>` or change this annotation contents.
Internally it is similar to filemodify 100644 on `<commit-ish>`
path (maybe split into subdirectories). It's not advised to
use any other commands to write to the `<notes_ref>` tree except
`filedeleteall` to delete all existing notes in this tree.
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 <commit-ish> 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 <commit-ish> LF
	data
....
+
See below for a detailed description of the `data` command.

In both formats `<commit-ish>` 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.

`original-oid`
~~~~~~~~~~~~~~
Provides the name of the object in the original source control system.
fast-import will simply ignore this directive, but filter processes
which operate on and modify the stream before feeding to fast-import
may have uses for this information

....
	'original-oid' SP <object-identifier> LF
....

where `<object-identifier>` is any string not containing LF.

`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
	mark?
	'from' SP <commit-ish> LF
	original-oid?
	'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 <commit-ish> LF)?
	LF?
....

For a detailed description of `<ref>` and `<commit-ish>` 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?
	original-oid?
	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).

`alias`
~~~~~~~
Record that a mark refers to a given object without first creating any
new object.

....
	'alias' LF
	mark
	'to' SP <commit-ish> LF
	LF?
....

For a detailed description of `<commit-ish>` see above under `from`.


`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.