mirror of
https://github.com/git/git
synced 2024-08-25 02:35:46 +00:00
[PATCH] Docs - tag object, git- prefix and s/changeset/commit/g
Add docs for tag type Rename commands to have git- prefix Rename changeset to commit throughout Signed-off-by: David Greaves <david@dgreaves.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
David Greaves
Linus Torvalds
parent
6c84e2e0c7
commit
7096a645cd
159
README
159
README
|
|
@ -31,9 +31,9 @@ build up a hierarchy of objects.
|
|||
|
||||
All objects have a statically determined "type" aka "tag", which is
|
||||
determined at object creation time, and which identifies the format of
|
||||
the object (i.e. how it is used, and how it can refer to other objects).
|
||||
There are currently three different object types: "blob", "tree" and
|
||||
"commit".
|
||||
the object (i.e. how it is used, and how it can refer to other
|
||||
objects). There are currently four different object types: "blob",
|
||||
"tree", "commit" and "tag".
|
||||
|
||||
A "blob" object cannot refer to any other object, and is, like the tag
|
||||
implies, a pure storage object containing some user data. It is used to
|
||||
|
|
@ -44,7 +44,7 @@ A "tree" object is an object that ties one or more "blob" objects into a
|
|||
directory structure. In addition, a tree object can refer to other tree
|
||||
objects, thus creating a directory hierarchy.
|
||||
|
||||
Finally, a "commit" object ties such directory hierarchies together into
|
||||
A "commit" object ties such directory hierarchies together into
|
||||
a DAG of revisions - each "commit" is associated with exactly one tree
|
||||
(the directory hierarchy at the time of the commit). In addition, a
|
||||
"commit" refers to one or more "parent" commit objects that describe the
|
||||
|
|
@ -79,9 +79,9 @@ size> + <byte\0> + <binary object data>.
|
|||
|
||||
The structured objects can further have their structure and
|
||||
connectivity to other objects verified. This is generally done with
|
||||
the "fsck-cache" program, which generates a full dependency graph of
|
||||
all objects, and verifies their internal consistency (in addition to
|
||||
just verifying their superficial consistency through the hash).
|
||||
the "git-fsck-cache" program, which generates a full dependency graph
|
||||
of all objects, and verifies their internal consistency (in addition
|
||||
to just verifying their superficial consistency through the hash).
|
||||
|
||||
The object types in some more detail:
|
||||
|
||||
|
|
@ -102,6 +102,9 @@ object. The object is totally independent of it's location in the
|
|||
directory tree, and renaming a file does not change the object that
|
||||
file is associated with in any way.
|
||||
|
||||
A blob is created with link:git-write-blob.html[git-write-blob] and
|
||||
it's data can be accessed by link:git-cat-file.html[git-cat-file]
|
||||
|
||||
Tree Object
|
||||
~~~~~~~~~~~
|
||||
The next hierarchical object type is the "tree" object. A tree object
|
||||
|
|
@ -138,65 +141,79 @@ 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.
|
||||
|
||||
A tree is created with link:git-write-tree.html[git-write-tree] and
|
||||
it's data can be accessed by link:git-ls-tree.html[git-ls-tree]
|
||||
|
||||
Changeset Object
|
||||
~~~~~~~~~~~~~~~~
|
||||
The "changeset" object is an object that introduces the notion of
|
||||
Commit Object
|
||||
~~~~~~~~~~~~~
|
||||
The "commit" 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:
|
||||
A "commit" is defined by the tree-object that it results in, the
|
||||
parent commits (zero, one or more) that led up to that point, and a
|
||||
comment on what happened. Again, a commit 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 change information. All of that is
|
||||
Note on commits: unlike real SCM's, commits 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 Object
|
||||
~~~~~~~~~~~~
|
||||
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.
|
||||
A commit is created with link:git-commit-tree.html[git-commit-tree] and
|
||||
it's data can be accessed by link:git-cat-file.html[git-cat-file]
|
||||
|
||||
Furthermore, since the SHA1 signature of a changeset refers to the
|
||||
Trust
|
||||
~~~~~
|
||||
An aside on the notion of "trust". 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 commit 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 the parent, a single named commit 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.
|
||||
way once you have the name of a commit.
|
||||
|
||||
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.
|
||||
name of a top-level commit. Your digital signature shows others
|
||||
that you trust that commit, and the immutability of the history of
|
||||
commits 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
|
||||
of the top commit, 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.
|
||||
To assist in this, git also provides the tag object...
|
||||
|
||||
Another way of saying the last point: "git" itself only handles
|
||||
content integrity, the trust has to come from outside.
|
||||
Tag Object
|
||||
~~~~~~~~~~
|
||||
Git provides the "tag" object to simplify creating, managing and
|
||||
exchanging symbolic and signed tokens. The "tag" object at its
|
||||
simplest simply symbolically identifies another object by containing
|
||||
the sha1, type and symbolic name.
|
||||
|
||||
However it can optionally contain additional signature information
|
||||
(which git doesn't care about as long as there's less than 8k of
|
||||
it). This can then be verified externally to git.
|
||||
|
||||
Note that despite the tag features, "git" itself only handles content
|
||||
integrity; the trust framework (and signature provision and
|
||||
verification) has to come from outside.
|
||||
|
||||
A tag is created with link:git-mktag.html[git-mktag] and
|
||||
it's data can be accessed by link:git-cat-file.html[git-cat-file]
|
||||
|
||||
The "index" aka "Current Directory Cache"
|
||||
-----------------------------------------
|
||||
|
|
@ -263,11 +280,11 @@ main combinations:
|
|||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
You update the index with information from the working directory with
|
||||
the "update-cache" command. You generally update the index
|
||||
information by just specifying the filename you want to update, like
|
||||
so:
|
||||
the link:git-update-cache.html[git-update-cache] command. You
|
||||
generally update the index information by just specifying the filename
|
||||
you want to update, like so:
|
||||
|
||||
update-cache filename
|
||||
git-update-cache filename
|
||||
|
||||
but to avoid common mistakes with filename globbing etc, the command
|
||||
will not normally add totally new entries or remove old entries,
|
||||
|
|
@ -284,7 +301,7 @@ removed. The only thing "--remove" means is that update-cache will be
|
|||
considering a removed file to be a valid thing, and if the file really
|
||||
does not exist any more, it will update the index accordingly.
|
||||
|
||||
As a special case, you can also do "update-cache --refresh", which
|
||||
As a special case, you can also do "git-update-cache --refresh", which
|
||||
will refresh the "stat" information of each index to match the current
|
||||
stat information. It will _not_ update the object status itself, and
|
||||
it will only update the fields that are used to quickly test whether
|
||||
|
|
@ -295,7 +312,7 @@ an object still matches its old backing store object.
|
|||
|
||||
You write your current index file to a "tree" object with the program
|
||||
|
||||
write-tree
|
||||
git-write-tree
|
||||
|
||||
that doesn't come with any options - it will just write out the
|
||||
current index into the set of tree objects that describe that state,
|
||||
|
|
@ -311,7 +328,7 @@ populate (and overwrite - don't do this if your index contains any
|
|||
unsaved state that you might want to restore later!) your current
|
||||
index. Normal operation is just
|
||||
|
||||
read-tree <sha1 of tree>
|
||||
git-read-tree <sha1 of tree>
|
||||
|
||||
and your index file will now be equivalent to the tree that you saved
|
||||
earlier. However, that is only your _index_ file: your working
|
||||
|
|
@ -324,20 +341,19 @@ You update your working directory from the index by "checking out"
|
|||
files. This is not a very common operation, since normally you'd just
|
||||
keep your files updated, and rather than write to your working
|
||||
directory, you'd tell the index files about the changes in your
|
||||
working directory (i.e. "update-cache").
|
||||
working directory (i.e. "git-update-cache").
|
||||
|
||||
However, if you decide to jump to a new version, or check out somebody
|
||||
else's version, or just restore a previous tree, you'd populate your
|
||||
index file with read-tree, and then you need to check out the result
|
||||
with
|
||||
|
||||
checkout-cache filename
|
||||
git-checkout-cache filename
|
||||
|
||||
or, if you want to check out all of the index, use "-a".
|
||||
|
||||
NOTE! checkout-cache normally refuses to overwrite old files, so if
|
||||
you have an old version of the tree already checked out, you will need
|
||||
to use the "-f" flag (_before_ the "-a" flag or the filename) to
|
||||
NOTE! git-checkout-cache normally refuses to overwrite old files, so
|
||||
if you have an old version of the tree already checked out, you will
|
||||
need to use the "-f" flag (_before_ the "-a" flag or the filename) to
|
||||
_force_ the checkout.
|
||||
|
||||
|
||||
|
|
@ -346,10 +362,10 @@ from one representation to the other:
|
|||
|
||||
5) Tying it all together
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
To commit a tree you have instantiated with "write-tree", you'd create
|
||||
a "commit" object that refers to that tree and the history behind it -
|
||||
most notably the "parent" commits that preceded it in history.
|
||||
To commit a tree you have instantiated with "git-write-tree", you'd
|
||||
create a "commit" object that refers to that tree and the history
|
||||
behind it - most notably the "parent" commits that preceded it in
|
||||
history.
|
||||
|
||||
Normally a "commit" has one parent: the previous state of the tree
|
||||
before a certain change was made. However, sometimes it can have two
|
||||
|
|
@ -364,15 +380,15 @@ and explains how we got there.
|
|||
You create a commit object by giving it the tree that describes the
|
||||
state at the time of the commit, and a list of parents:
|
||||
|
||||
commit-tree <tree> -p <parent> [-p <parent2> ..]
|
||||
git-commit-tree <tree> -p <parent> [-p <parent2> ..]
|
||||
|
||||
and then giving the reason for the commit on stdin (either through
|
||||
redirection from a pipe or file, or by just typing it at the tty).
|
||||
|
||||
commit-tree will return the name of the object that represents that
|
||||
commit, and you should save it away for later use. Normally, you'd
|
||||
commit a new "HEAD" state, and while git doesn't care where you save
|
||||
the note about that state, in practice we tend to just write the
|
||||
git-commit-tree will return the name of the object that represents
|
||||
that commit, and you should save it away for later use. Normally,
|
||||
you'd commit a new "HEAD" state, and while git doesn't care where you
|
||||
save the note about that state, in practice we tend to just write the
|
||||
result to the file ".git/HEAD", so that we can always see what the
|
||||
last committed state was.
|
||||
|
||||
|
|
@ -381,25 +397,27 @@ last committed state was.
|
|||
|
||||
You can examine the data represented in the object database and the
|
||||
index with various helper tools. For every object, you can use
|
||||
"cat-file" to examine details about the object:
|
||||
link:git-cat-file.html[git-cat-file] to examine details about the
|
||||
object:
|
||||
|
||||
cat-file -t <objectname>
|
||||
git-cat-file -t <objectname>
|
||||
|
||||
shows the type of the object, and once you have the type (which is
|
||||
usually implicit in where you find the object), you can use
|
||||
|
||||
cat-file blob|tree|commit <objectname>
|
||||
git-cat-file blob|tree|commit <objectname>
|
||||
|
||||
to show its contents. NOTE! Trees have binary content, and as a result
|
||||
there is a special helper for showing that content, called "ls-tree",
|
||||
which turns the binary content into a more easily readable form.
|
||||
there is a special helper for showing that content, called
|
||||
"git-ls-tree", which turns the binary content into a more easily
|
||||
readable form.
|
||||
|
||||
It's especially instructive to look at "commit" objects, since those
|
||||
tend to be small and fairly self-explanatory. In particular, if you
|
||||
follow the convention of having the top commit name in ".git/HEAD",
|
||||
you can do
|
||||
|
||||
cat-file commit $(cat .git/HEAD)
|
||||
git-cat-file commit $(cat .git/HEAD)
|
||||
|
||||
to see what the top commit was.
|
||||
|
||||
|
|
@ -420,13 +438,13 @@ state of the directory ("tree" object) at these points.
|
|||
To get the "base" for the merge, you first look up the common parent
|
||||
of two commits with
|
||||
|
||||
merge-base <commit1> <commit2>
|
||||
git-merge-base <commit1> <commit2>
|
||||
|
||||
which will return you the commit they are both based on. You should
|
||||
now look up the "tree" objects of those commits, which you can easily
|
||||
do with (for example)
|
||||
|
||||
cat-file commit <commitname> | head -1
|
||||
git-cat-file commit <commitname> | head -1
|
||||
|
||||
since the tree object information is always the first line in a commit
|
||||
object.
|
||||
|
|
@ -441,15 +459,16 @@ what you have in your current index anyway).
|
|||
|
||||
To do the merge, do
|
||||
|
||||
read-tree -m <origtree> <target1tree> <target2tree>
|
||||
git-read-tree -m <origtree> <target1tree> <target2tree>
|
||||
|
||||
which will do all trivial merge operations for you directly in the
|
||||
index file, and you can just write the result out with "write-tree".
|
||||
index file, and you can just write the result out with
|
||||
"git-write-tree".
|
||||
|
||||
NOTE! Because the merge is done in the index file, and not in your
|
||||
working directory, your working directory will no longer match your
|
||||
index. You can use "checkout-cache -f -a" to make the effect of the
|
||||
merge be seen in your working directory.
|
||||
index. You can use "git-checkout-cache -f -a" to make the effect of
|
||||
the merge be seen in your working directory.
|
||||
|
||||
NOTE2! Sadly, many merges aren't trivial. If there are files that have
|
||||
been added.moved or removed, or if both branches have modified the
|
||||
|
|
|
|||
Loading…
Reference in a new issue