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Documentation: reorganize cvs-migration.txt

Browse Source 
Modify cvs-migration.txt so it explains first how to develop against a
shared repository, then how to set up a shared repository, then how to
import a repository from cvs.  Though this seems chronologically
backwards, it's still readable in this order, and it puts the more
commonly needed material closer to the front.

Remove the annotate/pickaxe section; perhaps it can find a place elsewhere
in the future.  Remove most of the "why git is better than cvs" stuff from
the introduction.

Add some minor clarifications, including two that have come up several
times on the mailing list:

	1. Recommend committing any changes before running pull.
	2. Note that changes must be commited before they can be pushed.

Update the clone discussion to reflect the new --use-separate-remotes
default, and add a brief mention of git-cvsserver.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This commit is contained in:
J. Bruce Fields 2006-12-06 23:18:05 -05:00 committed by Junio C Hamano
parent de51faf388
commit cd976f5c52
1 changed files with 115 additions and 256 deletions
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371
Documentation/cvs-migration.txt
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@ -1,33 +1,106 @@
git for CVS users
=================
So you're a CVS user. That's OK, it's a treatable condition. The job of
this document is to put you on the road to recovery, by helping you
convert an existing cvs repository to git, and by showing you how to use a
git repository in a cvs-like fashion.
Git differs from CVS in that every working tree contains a repository with
a full copy of the project history, and no repository is inherently more
important than any other. However, you can emulate the CVS model by
designating a single shared repository which people can synchronize with;
this document explains how to do that.
Some basic familiarity with git is required. This
link:tutorial.html[tutorial introduction to git] should be sufficient.
First, note some ways that git differs from CVS:
Developing against a shared repository
--------------------------------------
* Commits are atomic and project-wide, not per-file as in CVS.
Suppose a shared repository is set up in /pub/repo.git on the host
foo.com. Then as an individual committer you can clone the shared
repository over ssh with:
* Offline work is supported: you can make multiple commits locally,
then submit them when you're ready.
------------------------------------------------
$ git clone foo.com:/pub/repo.git/ my-project
$ cd my-project
------------------------------------------------
* Branching is fast and easy.
and hack away. The equivalent of `cvs update` is
* Every working tree contains a repository with a full copy of the
project history, and no repository is inherently more important than
any other. However, you can emulate the CVS model by designating a
single shared repository which people can synchronize with; see below
for details.
------------------------------------------------
$ git pull origin
------------------------------------------------
* Since every working tree contains a repository, a commit in your
private repository will not publish your changes; it will only create
a revision. You have to "push" your changes to a public repository to
make them visible to others.
which merges in any work that others might have done since the clone
operation. If there are uncommitted changes in your working tree, commit
them first before running git pull.
[NOTE]
================================
The first `git clone` places the following in the
`my-project/.git/remotes/origin` file, and that's why the previous step
and the next step both work.
------------
URL: foo.com:/pub/project.git/
Pull: refs/heads/master:refs/remotes/origin/master
------------
================================
You can update the shared repository with your changes by first commiting
your changes, and then using:
------------------------------------------------
$ git push origin master
------------------------------------------------
to "push" those commits to the shared repository. If someone else has
updated the repository more recently, `git push`, like `cvs commit`, will
complain, in which case you must pull any changes before attempting the
push again.
In the `git push` command above we specify the name of the remote branch
to update (`master`). If we leave that out, `git push` tries to update
any branches in the remote repository that have the same name as a branch
in the local repository. So the last `push` can be done with either of:
------------
$ git push origin
$ git push foo.com:/pub/project.git/
------------
as long as the shared repository does not have any branches
other than `master`.
Setting Up a Shared Repository
------------------------------
We assume you have already created a git repository for your project,
possibly created from scratch or from a tarball (see the
link:tutorial.html[tutorial]), or imported from an already existing CVS
repository (see the next section).
If your project's working directory is /home/alice/myproject, you can
create a shared repository at /pub/repo.git with:
------------------------------------------------
$ git clone -bare /home/alice/myproject /pub/repo.git
------------------------------------------------
Next, give every team member read/write access to this repository. One
easy way to do this is to give all the team members ssh access to the
machine where the repository is hosted. If you don't want to give them a
full shell on the machine, there is a restricted shell which only allows
users to do git pushes and pulls; see gitlink:git-shell[1].
Put all the committers in the same group, and make the repository
writable by that group:
------------------------------------------------
$ cd /pub
$ chgrp -R $group repo.git
$ find repo.git -mindepth 1 -type d |xargs chmod ug+rwx,g+s
$ GIT_DIR=repo.git git repo-config core.sharedrepository true
------------------------------------------------
Make sure committers have a umask of at most 027, so that the directories
they create are writable and searchable by other group members.
Importing a CVS archive
-----------------------
@ -60,14 +133,32 @@ work, you must not modify the imported branches; instead, create new
branches for your own changes, and merge in the imported branches as
necessary.
Development Models
------------------
Advanced Shared Repository Management
-------------------------------------
Git allows you to specify scripts called "hooks" to be run at certain
points. You can use these, for example, to send all commits to the shared
repository to a mailing list. See link:hooks.html[Hooks used by git].
You can enforce finer grained permissions using update hooks. See
link:howto/update-hook-example.txt[Controlling access to branches using
update hooks].
Providing CVS Access to a git Repository
----------------------------------------
It is also possible to provide true CVS access to a git repository, so
that developers can still use CVS; see gitlink:git-cvsserver[1] for
details.
Alternative Development Models
------------------------------
CVS users are accustomed to giving a group of developers commit access to
a common repository. In the next section we'll explain how to do this
with git. However, the distributed nature of git allows other development
models, and you may want to first consider whether one of them might be a
better fit for your project.
a common repository. As we've seen, this is also possible with git.
However, the distributed nature of git allows other development models,
and you may want to first consider whether one of them might be a better
fit for your project.
For example, you can choose a single person to maintain the project's
primary public repository. Other developers then clone this repository
@ -80,235 +171,3 @@ variants of this model.
With a small group, developers may just pull changes from each other's
repositories without the need for a central maintainer.
Creating a Shared Repository
----------------------------
Start with an ordinary git working directory containing the project, and
remove the checked-out files, keeping just the bare .git directory:
------------------------------------------------
$ mv project/.git /pub/repo.git
$ rm -r project/
------------------------------------------------
Next, give every team member read/write access to this repository. One
easy way to do this is to give all the team members ssh access to the
machine where the repository is hosted. If you don't want to give them a
full shell on the machine, there is a restricted shell which only allows
users to do git pushes and pulls; see gitlink:git-shell[1].
Put all the committers in the same group, and make the repository
writable by that group:
------------------------------------------------
$ chgrp -R $group repo.git
$ find repo.git -mindepth 1 -type d |xargs chmod ug+rwx,g+s
$ GIT_DIR=repo.git git repo-config core.sharedrepository true
------------------------------------------------
Make sure committers have a umask of at most 027, so that the directories
they create are writable and searchable by other group members.
Performing Development on a Shared Repository
---------------------------------------------
Suppose a repository is now set up in /pub/repo.git on the host
foo.com. Then as an individual committer you can clone the shared
repository:
------------------------------------------------
$ git clone foo.com:/pub/repo.git/ my-project
$ cd my-project
------------------------------------------------
and hack away. The equivalent of `cvs update` is
------------------------------------------------
$ git pull origin
------------------------------------------------
which merges in any work that others might have done since the clone
operation.
[NOTE]
================================
The first `git clone` places the following in the
`my-project/.git/remotes/origin` file, and that's why the previous step
and the next step both work.
------------
URL: foo.com:/pub/project.git/ my-project
Pull: master:origin
------------
================================
You can update the shared repository with your changes by first commiting
your changes, and then using:
------------------------------------------------
$ git push origin master
------------------------------------------------
to "push" those commits to the shared repository. If someone else has
updated the repository more recently, `git push`, like `cvs commit`, will
complain, in which case you must pull any changes before attempting the
push again.
In the `git push` command above we specify the name of the remote branch
to update (`master`). If we leave that out, `git push` tries to update
any branches in the remote repository that have the same name as a branch
in the local repository. So the last `push` can be done with either of:
------------
$ git push origin
$ git push repo.shared.xz:/pub/scm/project.git/
------------
as long as the shared repository does not have any branches
other than `master`.
[NOTE]
============
Because of this behavior, if the shared repository and the developer's
repository both have branches named `origin`, then a push like the above
attempts to update the `origin` branch in the shared repository from the
developer's `origin` branch. The results may be unexpected, so it's
usually best to remove any branch named `origin` from the shared
repository.
============
Advanced Shared Repository Management
-------------------------------------
Git allows you to specify scripts called "hooks" to be run at certain
points. You can use these, for example, to send all commits to the shared
repository to a mailing list. See link:hooks.html[Hooks used by git].
You can enforce finer grained permissions using update hooks. See
link:howto/update-hook-example.txt[Controlling access to branches using
update hooks].
CVS annotate
------------
So, something has gone wrong, and you don't know whom to blame, and
you're an ex-CVS user and used to do "cvs annotate" to see who caused
the breakage. You're looking for the "git annotate", and it's just
claiming not to find such a script. You're annoyed.
Yes, that's right. Core git doesn't do "annotate", although it's
technically possible, and there are at least two specialized scripts out
there that can be used to get equivalent information (see the git
mailing list archives for details).
git has a couple of alternatives, though, that you may find sufficient
or even superior depending on your use. One is called "git-whatchanged"
(for obvious reasons) and the other one is called "pickaxe" ("a tool for
the software archaeologist").
The "git-whatchanged" script is a truly trivial script that can give you
a good overview of what has changed in a file or a directory (or an
arbitrary list of files or directories). The "pickaxe" support is an
additional layer that can be used to further specify exactly what you're
looking for, if you already know the specific area that changed.
Let's step back a bit and think about the reason why you would
want to do "cvs annotate a-file.c" to begin with.
You would use "cvs annotate" on a file when you have trouble
with a function (or even a single "if" statement in a function)
that happens to be defined in the file, which does not do what
you want it to do. And you would want to find out why it was
written that way, because you are about to modify it to suit
your needs, and at the same time you do not want to break its
current callers. For that, you are trying to find out why the
original author did things that way in the original context.
Many times, it may be enough to see the commit log messages of
commits that touch the file in question, possibly along with the
patches themselves, like this:
$ git-whatchanged -p a-file.c
This will show log messages and patches for each commit that
touches a-file.
This, however, may not be very useful when this file has many
modifications that are not related to the piece of code you are
interested in. You would see many log messages and patches that
do not have anything to do with the piece of code you are
interested in. As an example, assuming that you have this piece
of code that you are interested in in the HEAD version:
if (frotz) {
nitfol();
}
you would use git-rev-list and git-diff-tree like this:
$ git-rev-list HEAD |
git-diff-tree --stdin -v -p -S'if (frotz) {
nitfol();
}'
We have already talked about the "\--stdin" form of git-diff-tree
command that reads the list of commits and compares each commit
with its parents (otherwise you should go back and read the tutorial).
The git-whatchanged command internally runs
the equivalent of the above command, and can be used like this:
$ git-whatchanged -p -S'if (frotz) {
nitfol();
}'
When the -S option is used, git-diff-tree command outputs
differences between two commits only if one tree has the
specified string in a file and the corresponding file in the
other tree does not. The above example looks for a commit that
has the "if" statement in it in a file, but its parent commit
does not have it in the same shape in the corresponding file (or
the other way around, where the parent has it and the commit
does not), and the differences between them are shown, along
with the commit message (thanks to the -v flag). It does not
show anything for commits that do not touch this "if" statement.
Also, in the original context, the same statement might have
appeared at first in a different file and later the file was
renamed to "a-file.c". CVS annotate would not help you to go
back across such a rename, but git would still help you in such
a situation. For that, you can give the -C flag to
git-diff-tree, like this:
$ git-whatchanged -p -C -S'if (frotz) {
nitfol();
}'
When the -C flag is used, file renames and copies are followed.
So if the "if" statement in question happens to be in "a-file.c"
in the current HEAD commit, even if the file was originally
called "o-file.c" and then renamed in an earlier commit, or if
the file was created by copying an existing "o-file.c" in an
earlier commit, you will not lose track. If the "if" statement
did not change across such a rename or copy, then the commit that
does rename or copy would not show in the output, and if the
"if" statement was modified while the file was still called
"o-file.c", it would find the commit that changed the statement
when it was in "o-file.c".
NOTE: The current version of "git-diff-tree -C" is not eager
enough to find copies, and it will miss the fact that a-file.c
was created by copying o-file.c unless o-file.c was somehow
changed in the same commit.
You can use the --pickaxe-all flag in addition to the -S flag.
This causes the differences from all the files contained in
those two commits, not just the differences between the files
that contain this changed "if" statement:
$ git-whatchanged -p -C -S'if (frotz) {
nitfol();
}' --pickaxe-all
NOTE: This option is called "--pickaxe-all" because -S
option is internally called "pickaxe", a tool for software
archaeologists.