+////////////////////////////////////////////////////////////////
GIT - the stupid content tracker
+////////////////////////////////////////////////////////////////
+
"git" can mean anything, depending on your mood.
- random three-letter combination that is pronounceable, and not
actually used by any common UNIX command. The fact that it is a
- mispronounciation of "get" may or may not be relevant.
+ mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the
dictionary of slang.
- "global information tracker": you're in a good mood, and it actually
- works for you. Angels sing, and a light suddenly fills the room.
+ works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks
-This is a stupid (but extremely fast) directory content manager. It
-doesn't do a whole lot, but what it _does_ do is track directory
-contents efficiently.
-
-There are two object abstractions: the "object database", and the
-"current directory cache".
-
- The Object Database (SHA1_FILE_DIRECTORY)
-
-The object database is literally just a content-addressable collection
-of objects. All objects are named by their content, which is
-approximated by the SHA1 hash of the object itself. Objects may refer
-to other objects (by referencing their SHA1 hash), and so you can build
-up a hierarchy of objects.
-
-There are several kinds of objects in the content-addressable collection
-database. They are all in deflated with zlib, and start off with a tag
-of their type, and size information about the data. The SHA1 hash is
-always the hash of the _compressed_ object, not the original one.
-
-In particular, the consistency of an object can always be tested
-independently of the contents or the type of the object: all objects can
-be validated by verifying that (a) their hashes match the content of the
-file and (b) the object successfully inflates to a stream of bytes that
-forms a sequence of <ascii tag without space> + <space> + <ascii decimal
-size> + <byte\0> + <binary object data>.
-
-BLOB: A "blob" object is nothing but a binary blob of data, and doesn't
-refer to anything else. There is no signature or any other verification
-of the data, so while the object is consistent (it _is_ indexed by its
-sha1 hash, so the data itself is certainly correct), it has absolutely
-no other attributes. No name associations, no permissions. It is
-purely a blob of data (ie normally "file contents").
-
-TREE: The next hierarchical object type is the "tree" object. A tree
-object is a list of permission/name/blob data, sorted by name. In other
-words the tree object is uniquely determined by the set contents, and so
-two separate but identical trees will always share the exact same
-object.
-
-Again, a "tree" object is just a pure data abstraction: it has no
-history, no signatures, no verification of validity, except that the
-contents are again protected by the hash itself. So you can trust the
-contents of a tree, the same way you can trust the contents of a blob,
-but you don't know where those contents _came_ from.
-
-Side note on trees: since a "tree" object is a sorted list of
-"filename+content", you can create a diff between two trees without
-actually having to unpack two trees. Just ignore all common parts, and
-your diff will look right. In other words, you can effectively (and
-efficiently) tell the difference between any two random trees by O(n)
-where "n" is the size of the difference, rather than the size of the
-tree.
-
-Side note 2 on trees: since the name of a "blob" depends entirely and
-exclusively on its contents (ie there are no names or permissions
-involved), you can see trivial renames or permission changes by noticing
-that the blob stayed the same. However, renames with data changes need
-a smarter "diff" implementation.
-
-CHANGESET: The "changeset" object is an object that introduces the
-notion of history into the picture. In contrast to the other objects,
-it doesn't just describe the physical state of a tree, it describes how
-we got there, and why.
-
-A "changeset" is defined by the tree-object that it results in, the
-parent changesets (zero, one or more) that led up to that point, and a
-comment on what happened. Again, a changeset is not trusted per se:
-the contents are well-defined and "safe" due to the cryptographically
-strong signatures at all levels, but there is no reason to believe that
-the tree is "good" or that the merge information makes sense. The
-parents do not have to actually have any relationship with the result,
-for example.
-
-Note on changesets: unlike real SCM's, changesets do not contain rename
-information or file mode chane information. All of that is implicit in
-the trees involved (the result tree, and the result trees of the
-parents), and describing that makes no sense in this idiotic file
-manager.
-
-TRUST: The notion of "trust" is really outside the scope of "git", but
-it's worth noting a few things. First off, since everything is hashed
-with SHA1, you _can_ trust that an object is intact and has not been
-messed with by external sources. So the name of an object uniquely
-identifies a known state - just not a state that you may want to trust.
-
-Furthermore, since the SHA1 signature of a changeset refers to the
-SHA1 signatures of the tree it is associated with and the signatures
-of the parent, a single named changeset specifies uniquely a whole
-set of history, with full contents. You can't later fake any step of
-the way once you have the name of a changeset.
-
-So to introduce some real trust in the system, the only thing you need
-to do is to digitally sign just _one_ special note, which includes the
-name of a top-level changeset. Your digital signature shows others that
-you trust that changeset, and the immutability of the history of
-changesets tells others that they can trust the whole history.
-
-In other words, you can easily validate a whole archive by just sending
-out a single email that tells the people the name (SHA1 hash) of the top
-changeset, and digitally sign that email using something like GPG/PGP.
-
-In particular, you can also have a separate archive of "trust points" or
-tags, which document your (and other peoples) trust. You may, of
-course, archive these "certificates of trust" using "git" itself, but
-it's not something "git" does for you.
-
-Another way of saying the same thing: "git" itself only handles content
-integrity, the trust has to come from outside.
-
- Current Directory Cache (".git/index")
-
-The "current directory cache" is a simple binary file, which contains an
-efficient representation of a virtual directory content at some random
-time. It does so by a simple array that associates a set of names,
-dates, permissions and content (aka "blob") objects together. The cache
-is always kept ordered by name, and names are unique at any point in
-time, but the cache has no long-term meaning, and can be partially
-updated at any time.
-
-In particular, the "current directory cache" certainly does not need to
-be consistent with the current directory contents, but it has two very
-important attributes:
-
- (a) it can re-generate the full state it caches (not just the directory
- structure: through the "blob" object it can regenerate the data too)
-
- As a special case, there is a clear and unambiguous one-way mapping
- from a current directory cache to a "tree object", which can be
- efficiently created from just the current directory cache without
- actually looking at any other data. So a directory cache at any
- one time uniquely specifies one and only one "tree" object (but
- has additional data to make it easy to match up that tree object
- with what has happened in the directory)
-
-
-and
-
- (b) it has efficient methods for finding inconsistencies between that
- cached state ("tree object waiting to be instantiated") and the
- current state.
-
-Those are the two ONLY things that the directory cache does. It's a
-cache, and the normal operation is to re-generate it completely from a
-known tree object, or update/compare it with a live tree that is being
-developed. If you blow the directory cache away entirely, you haven't
-lost any information as long as you have the name of the tree that it
-described.
-
-(But directory caches can also have real information in them: in
-particular, they can have the representation of an intermediate tree
-that has not yet been instantiated. So they do have meaning and usage
-outside of caching - in one sense you can think of the current directory
-cache as being the "work in progress" towards a tree commit).
+Git is a fast, scalable, distributed revision control system with an
+unusually rich command set that provides both high-level operations
+and full access to internals.
+
+Git is an Open Source project covered by the GNU General Public License.
+It was originally written by Linus Torvalds with help of a group of
+hackers around the net. It is currently maintained by Junio C Hamano.
+
+Please read the file INSTALL for installation instructions.
+See Documentation/tutorial.txt to get started, then see
+Documentation/everyday.txt for a useful minimum set of commands,
+and "man git-commandname" for documentation of each command.
+CVS users may also want to read Documentation/cvs-migration.txt.
+
+Many Git online resources are accessible from http://git.or.cz/
+including full documentation and Git related tools.
+
+The user discussion and development of Git take place on the Git
+mailing list -- everyone is welcome to post bug reports, feature
+requests, comments and patches to git@vger.kernel.org. To subscribe
+to the list, send an email with just "subscribe git" in the body to
+majordomo@vger.kernel.org. The mailing list archives are available at
+http://marc.theaimsgroup.com/?l=git and other archival sites.