* Re: [Qemu-devel] Switch to GIT. Why?
2009-04-26 7:13 ` M. Warner Losh
@ 2009-04-26 8:15 ` Ralf Baechle
2009-04-27 13:10 ` Lennart Sorensen
1 sibling, 0 replies; 9+ messages in thread
From: Ralf Baechle @ 2009-04-26 8:15 UTC (permalink / raw)
To: M. Warner Losh; +Cc: mle+tools, qemu-devel
On Sun, Apr 26, 2009 at 01:13:20AM -0600, M. Warner Losh wrote:
> : > Is it possible to set it up so that GIT has an SVN back-end?
> :
> : Not that I know of.
>
> I thought I saw an email go by that it was already setup...
I assume you're talking about the git-svn command?
Just like git's CVS interoperability it's a nice tool but in the end it
should only be used to make the pains of migration more bareable. I
don't think git-cvsserver for example is a great thing in the longer run
nor does git-svn seem to be.
Ralf
GIT-SVN(1) Git Manual GIT-SVN(1)
NAME
git-svn - Bidirectional operation between a single Subversion branch
and git
SYNOPSIS
git svn <command> [options] [arguments]
DESCRIPTION
git-svn is a simple conduit for changesets between Subversion and git.
It provides a bidirectional flow of changes between a Subversion and a
git repository.
git-svn can track a single Subversion branch simply by using a URL to
the branch, follow branches laid out in the Subversion recommended
method (trunk, branches, tags directories) with the --stdlayout option,
or follow branches in any layout with the -T/-t/-b options (see options
to init below, and also the clone command).
Once tracking a Subversion branch (with any of the above methods), the
git repository can be updated from Subversion by the fetch command and
Subversion updated from git by the dcommit command.
COMMANDS
init
Initializes an empty git repository with additional metadata
directories for git-svn. The Subversion URL may be specified as a
command-line argument, or as full URL arguments to -T/-t/-b.
Optionally, the target directory to operate on can be specified as
a second argument. Normally this command initializes the current
directory.
-T<trunk_subdir>, --trunk=<trunk_subdir>, -t<tags_subdir>,
--tags=<tags_subdir>, -b<branches_subdir>,
--branches=<branches_subdir>, -s, --stdlayout
These are optional command-line options for init. Each of these
flags can point to a relative repository path
(--tags=project/tags´) or a full url
(--tags=https://foo.org/project/tags). The option --stdlayout
is a shorthand way of setting trunk,tags,branches as the
relative paths, which is the Subversion default. If any of the
other options are given as well, they take precedence.
--no-metadata
Set the noMetadata option in the [svn-remote] config.
--use-svm-props
Set the useSvmProps option in the [svn-remote] config.
--use-svnsync-props
Set the useSvnsyncProps option in the [svn-remote] config.
--rewrite-root=<URL>
Set the rewriteRoot option in the [svn-remote] config.
--use-log-author
When retrieving svn commits into git (as part of fetch, rebase,
or dcommit operations), look for the first From: or
Signed-off-by: line in the log message and use that as the
author string.
--add-author-from
When committing to svn from git (as part of commit or dcommit
operations), if the existing log message doesn´t already have a
From: or Signed-off-by: line, append a From: line based on the
git commit´s author string. If you use this, then
--use-log-author will retrieve a valid author string for all
commits.
--username=<USER>
For transports that SVN handles authentication for (http,
https, and plain svn), specify the username. For other
transports (eg svn+ssh://), you must include the username in
the URL, eg svn+ssh://foo@svn.bar.com/project
--prefix=<prefix>
This allows one to specify a prefix which is prepended to the
names of remotes if trunk/branches/tags are specified. The
prefix does not automatically include a trailing slash, so be
sure you include one in the argument if that is what you want.
If --branches/-b is specified, the prefix must include a
trailing slash. Setting a prefix is useful if you wish to track
multiple projects that share a common repository.
fetch
Fetch unfetched revisions from the Subversion remote we are
tracking. The name of the [svn-remote "..."] section in the
.git/config file may be specified as an optional command-line
argument.
clone
Runs init and fetch. It will automatically create a directory based
on the basename of the URL passed to it; or if a second argument is
passed; it will create a directory and work within that. It accepts
all arguments that the init and fetch commands accept; with the
exception of --fetch-all. After a repository is cloned, the fetch
command will be able to update revisions without affecting the
working tree; and the rebase command will be able to update the
working tree with the latest changes.
rebase
This fetches revisions from the SVN parent of the current HEAD and
rebases the current (uncommitted to SVN) work against it.
This works similarly to svn update or git-pull except that it
preserves linear history with git-rebase instead of git-merge for
ease of dcommitting with git-svn.
This accepts all options that git-svn fetch and git-rebase accept.
However, --fetch-all only fetches from the current [svn-remote],
and not all [svn-remote] definitions.
Like git-rebase; this requires that the working tree be clean and
have no uncommitted changes.
-l, --local
Do not fetch remotely; only run git-rebase against the last
fetched commit from the upstream SVN.
dcommit
Commit each diff from a specified head directly to the SVN
repository, and then rebase or reset (depending on whether or not
there is a diff between SVN and head). This will create a revision
in SVN for each commit in git. It is recommended that you run
git-svn fetch and rebase (not pull or merge) your commits against
the latest changes in the SVN repository. An optional command-line
argument may be specified as an alternative to HEAD. This is
advantageous over set-tree (below) because it produces cleaner,
more linear history.
--no-rebase
After committing, do not rebase or reset.
--commit-url <URL>
Commit to this SVN URL (the full path). This is intended to
allow existing git-svn repositories created with one transport
method (e.g. svn:// or http:// for anonymous read) to be reused
if a user is later given access to an alternate transport
method (e.g. svn+ssh:// or https://) for commit.
Using this option for any other purpose (don´t ask)
is very strongly discouraged.
log
This should make it easy to look up svn log messages when svn users
refer to -r/--revision numbers.
The following features from ‘svn log´ are supported:
--revision=<n>[:<n>]
is supported, non-numeric args are not: HEAD, NEXT, BASE, PREV,
etc ...
-v/--verbose
it´s not completely compatible with the --verbose output in svn
log, but reasonably close.
--limit=<n>
is NOT the same as --max-count, doesn´t count merged/excluded
commits
--incremental
supported
New features:
--show-commit
shows the git commit sha1, as well
--oneline
our version of --pretty=oneline
Note
SVN itself only stores times in UTC and nothing else. The
regular svn client converts the UTC time to the local time (or
based on the TZ= environment). This command has the same
behaviour.
Any other arguments are passed directly to git-log
blame
Show what revision and author last modified each line of a file.
The output of this mode is format-compatible with the output of
‘svn blame´ by default. Like the SVN blame command, local
uncommitted changes in the working copy are ignored; the version of
the file in the HEAD revision is annotated. Unknown arguments are
passed directly to git-blame.
--git-format
Produce output in the same format as git-blame, but with SVN
revision numbers instead of git commit hashes. In this mode,
changes that haven´t been committed to SVN (including local
working-copy edits) are shown as revision 0.
find-rev
When given an SVN revision number of the form rN, returns the
corresponding git commit hash (this can optionally be followed by a
tree-ish to specify which branch should be searched). When given a
tree-ish, returns the corresponding SVN revision number.
set-tree
You should consider using dcommit instead of this command. Commit
specified commit or tree objects to SVN. This relies on your
imported fetch data being up-to-date. This makes absolutely no
attempts to do patching when committing to SVN, it simply
overwrites files with those specified in the tree or commit. All
merging is assumed to have taken place independently of git-svn
functions.
create-ignore
Recursively finds the svn:ignore property on directories and
creates matching .gitignore files. The resulting files are staged
to be committed, but are not committed. Use -r/--revision to refer
to a specific revision.
show-ignore
Recursively finds and lists the svn:ignore property on directories.
The output is suitable for appending to the $GIT_DIR/info/exclude
file.
commit-diff
Commits the diff of two tree-ish arguments from the command-line.
This command does not rely on being inside an git-svn init-ed
repository. This command takes three arguments, (a) the original
tree to diff against, (b) the new tree result, (c) the URL of the
target Subversion repository. The final argument (URL) may be
omitted if you are working from a git-svn-aware repository (that
has been init-ed with git-svn). The -r<revision> option is required
for this.
info
Shows information about a file or directory similar to what ‘svn
info´ provides. Does not currently support a -r/--revision
argument. Use the --url option to output only the value of the URL:
field.
proplist
Lists the properties stored in the Subversion repository about a
given file or directory. Use -r/--revision to refer to a specific
Subversion revision.
propget
Gets the Subversion property given as the first argument, for a
file. A specific revision can be specified with -r/--revision.
show-externals
Shows the Subversion externals. Use -r/--revision to specify a
specific revision.
OPTIONS
--shared[={false|true|umask|group|all|world|everybody}],
--template=<template_directory>
Only used with the init command. These are passed directly to
git-init.
-r <ARG>, --revision <ARG>
Used with the fetch command.
This allows revision ranges for partial/cauterized history to be
supported. $NUMBER, $NUMBER1:$NUMBER2 (numeric ranges),
$NUMBER:HEAD, and BASE:$NUMBER are all supported.
This can allow you to make partial mirrors when running fetch; but
is generally not recommended because history will be skipped and
lost.
-, --stdin
Only used with the set-tree command.
Read a list of commits from stdin and commit them in reverse order.
Only the leading sha1 is read from each line, so git-rev-list
--pretty=oneline output can be used.
--rmdir
Only used with the dcommit, set-tree and commit-diff commands.
Remove directories from the SVN tree if there are no files left
behind. SVN can version empty directories, and they are not removed
by default if there are no files left in them. git cannot version
empty directories. Enabling this flag will make the commit to SVN
act like git.
config key: svn.rmdir
-e, --edit
Only used with the dcommit, set-tree and commit-diff commands.
Edit the commit message before committing to SVN. This is off by
default for objects that are commits, and forced on when committing
tree objects.
config key: svn.edit
-l<num>, --find-copies-harder
Only used with the dcommit, set-tree and commit-diff commands.
They are both passed directly to git-diff-tree; see git-diff-
tree(1) for more information.
config key: svn.l
config key: svn.findcopiesharder
-A<filename>, --authors-file=<filename>
Syntax is compatible with the file used by git-cvsimport:
.ft C
loginname = Joe User <user@example.com>
.ft
If this option is specified and git-svn encounters an SVN committer
name that does not exist in the authors-file, git-svn will abort
operation. The user will then have to add the appropriate entry.
Re-running the previous git-svn command after the authors-file is
modified should continue operation.
config key: svn.authorsfile
-q, --quiet
Make git-svn less verbose.
--repack[=<n>], --repack-flags=<flags>
These should help keep disk usage sane for large fetches with many
revisions.
--repack takes an optional argument for the number of revisions to
fetch before repacking. This defaults to repacking every 1000
commits fetched if no argument is specified.
--repack-flags are passed directly to git-repack.
config key: svn.repack
config key: svn.repackflags
-m, --merge, -s<strategy>, --strategy=<strategy>
These are only used with the dcommit and rebase commands.
Passed directly to git-rebase when using dcommit if a git-reset
cannot be used (see dcommit).
-n, --dry-run
This can be used with the dcommit and rebase commands.
For dcommit, print out the series of git arguments that would show
which diffs would be committed to SVN.
For rebase, display the local branch associated with the upstream
svn repository associated with the current branch and the URL of
svn repository that will be fetched from.
ADVANCED OPTIONS
-i<GIT_SVN_ID>, --id <GIT_SVN_ID>
This sets GIT_SVN_ID (instead of using the environment). This
allows the user to override the default refname to fetch from when
tracking a single URL. The log and dcommit commands no longer
require this switch as an argument.
-R<remote name>, --svn-remote <remote name>
Specify the [svn-remote "<remote name>"] section to use, this
allows SVN multiple repositories to be tracked. Default: "svn"
--follow-parent
This is especially helpful when we´re tracking a directory that has
been moved around within the repository, or if we started tracking
a branch and never tracked the trunk it was descended from. This
feature is enabled by default, use --no-follow-parent to disable
it.
config key: svn.followparent
CONFIG FILE-ONLY OPTIONS
svn.noMetadata, svn-remote.<name>.noMetadata
This gets rid of the git-svn-id: lines at the end of every commit.
If you lose your .git/svn/git-svn/.rev_db file, git-svn will not be
able to rebuild it and you won´t be able to fetch again, either.
This is fine for one-shot imports.
The git-svn log command will not work on repositories using this,
either. Using this conflicts with the useSvmProps option for
(hopefully) obvious reasons.
svn.useSvmProps, svn-remote.<name>.useSvmProps
This allows git-svn to re-map repository URLs and UUIDs from
mirrors created using SVN::Mirror (or svk) for metadata.
If an SVN revision has a property, "svm:headrev", it is likely that
the revision was created by SVN::Mirror (also used by SVK). The
property contains a repository UUID and a revision. We want to make
it look like we are mirroring the original URL, so introduce a
helper function that returns the original identity URL and UUID,
and use it when generating metadata in commit messages.
svn.useSvnsyncProps, svn-remote.<name>.useSvnsyncprops
Similar to the useSvmProps option; this is for users of the
svnsync(1) command distributed with SVN 1.4.x and later.
svn-remote.<name>.rewriteRoot
This allows users to create repositories from alternate URLs. For
example, an administrator could run git-svn on the server locally
(accessing via file://) but wish to distribute the repository with
a public http:// or svn:// URL in the metadata so users of it will
see the public URL.
Since the noMetadata, rewriteRoot, useSvnsyncProps and useSvmProps
options all affect the metadata generated and used by git-svn; they
must be set in the configuration file before any history is imported
and these settings should never be changed once they are set.
Additionally, only one of these four options can be used per-svn-remote
section because they affect the git-svn-id: metadata line.
BASIC EXAMPLES
Tracking and contributing to the trunk of a Subversion-managed project:
.ft C
# Clone a repo (like git clone):
git svn clone http://svn.example.com/project/trunk
# Enter the newly cloned directory:
cd trunk
# You should be on master branch, double-check with git-branch
git branch
# Do some work and commit locally to git:
git commit ...
# Something is committed to SVN, rebase your local changes against the
# latest changes in SVN:
git svn rebase
# Now commit your changes (that were committed previously using git) to SVN,
# as well as automatically updating your working HEAD:
git svn dcommit
# Append svn:ignore settings to the default git exclude file:
git svn show-ignore >> .git/info/exclude
.ft
Tracking and contributing to an entire Subversion-managed project
(complete with a trunk, tags and branches):
.ft C
# Clone a repo (like git clone):
git svn clone http://svn.example.com/project -T trunk -b branches -t tags
# View all branches and tags you have cloned:
git branch -r
# Reset your master to trunk (or any other branch, replacing ´trunk´
# with the appropriate name):
git reset --hard remotes/trunk
# You may only dcommit to one branch/tag/trunk at a time. The usage
# of dcommit/rebase/show-ignore should be the same as above.
.ft
The initial git-svn clone can be quite time-consuming (especially for
large Subversion repositories). If multiple people (or one person with
multiple machines) want to use git-svn to interact with the same
Subversion repository, you can do the initial git-svn clone to a
repository on a server and have each person clone that repository with
git-clone:
.ft C
# Do the initial import on a server
ssh server "cd /pub && git svn clone http://svn.example.com/project
# Clone locally - make sure the refs/remotes/ space matches the server
mkdir project
cd project
git init
git remote add origin server:/pub/project
git config --add remote.origin.fetch ´+refs/remotes/*:refs/remotes/*´
git fetch
# Create a local branch from one of the branches just fetched
git checkout -b master FETCH_HEAD
# Initialize git-svn locally (be sure to use the same URL and -T/-b/-t options as were used on server)
git svn init http://svn.example.com/project
# Pull the latest changes from Subversion
git svn rebase
.ft
REBASE VS. PULL/MERGE
Originally, git-svn recommended that the remotes/git-svn branch be
pulled or merged from. This is because the author favored git svn
set-tree B to commit a single head rather than the git svn set-tree
A..B notation to commit multiple commits.
If you use git svn set-tree A..B to commit several diffs and you do not
have the latest remotes/git-svn merged into my-branch, you should use
git svn rebase to update your work branch instead of git pull or git
merge. pull/‘merge´ can cause non-linear history to be flattened when
committing into SVN, which can lead to merge commits reversing previous
commits in SVN.
DESIGN PHILOSOPHY
Merge tracking in Subversion is lacking and doing branched development
with Subversion can be cumbersome as a result. While git-svn can track
copy history (including branches and tags) for repositories adopting a
standard layout, it cannot yet represent merge history that happened
inside git back upstream to SVN users. Therefore it is advised that
users keep history as linear as possible inside git to ease
compatibility with SVN (see the CAVEATS section below).
CAVEATS
For the sake of simplicity and interoperating with a less-capable
system (SVN), it is recommended that all git-svn users clone, fetch and
dcommit directly from the SVN server, and avoid all
git-clone/pull/merge/push operations between git repositories and
branches. The recommended method of exchanging code between git
branches and users is git-format-patch and git-am, or just ´dcommit´ing
to the SVN repository.
Running git-merge or git-pull is NOT recommended on a branch you plan
to dcommit from. Subversion does not represent merges in any reasonable
or useful fashion; so users using Subversion cannot see any merges
you´ve made. Furthermore, if you merge or pull from a git branch that
is a mirror of an SVN branch, dcommit may commit to the wrong branch.
git-clone does not clone branches under the refs/remotes/ hierarchy or
any git-svn metadata, or config. So repositories created and managed
with using git-svn should use rsync for cloning, if cloning is to be
done at all.
Since dcommit uses rebase internally, any git branches you git-push to
before dcommit on will require forcing an overwrite of the existing ref
on the remote repository. This is generally considered bad practice,
see the git-push(1) documentation for details.
Do not use the --amend option of git-commit(1) on a change you´ve
already dcommitted. It is considered bad practice to --amend commits
you´ve already pushed to a remote repository for other users, and
dcommit with SVN is analogous to that.
BUGS
We ignore all SVN properties except svn:executable. Any unhandled
properties are logged to $GIT_DIR/svn/<refname>/unhandled.log
Renamed and copied directories are not detected by git and hence not
tracked when committing to SVN. I do not plan on adding support for
this as it´s quite difficult and time-consuming to get working for all
the possible corner cases (git doesn´t do it, either). Committing
renamed and copied files are fully supported if they´re similar enough
for git to detect them.
CONFIGURATION
git-svn stores [svn-remote] configuration information in the repository
.git/config file. It is similar the core git [remote] sections except
fetch keys do not accept glob arguments; but they are instead handled
by the branches and tags keys. Since some SVN repositories are oddly
configured with multiple projects glob expansions such those listed
below are allowed:
.ft C
[svn-remote "project-a"]
url = http://server.org/svn
branches = branches/*/project-a:refs/remotes/project-a/branches/*
tags = tags/*/project-a:refs/remotes/project-a/tags/*
trunk = trunk/project-a:refs/remotes/project-a/trunk
.ft
Keep in mind that the (asterisk) wildcard of the local ref (right of
the :) *must be the farthest right path component; however the remote
wildcard may be anywhere as long as it´s own independent path component
(surrounded by / or EOL). This type of configuration is not
automatically created by init and should be manually entered with a
text-editor or using git-config.
SEE ALSO
git-rebase(1)
AUTHOR
Written by Eric Wong <normalperson@yhbt.net>.
DOCUMENTATION
Written by Eric Wong <normalperson@yhbt.net>.
Git 1.6.0.6 03/02/2009 GIT-SVN(1)
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