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Re: [Qemu-devel] Switch to GIT. Why?

From: Ralf Baechle
Subject: Re: [Qemu-devel] Switch to GIT. Why?
Date: Sun, 26 Apr 2009 10:15:16 +0200
User-agent: Mutt/1.5.18 (2008-05-17)

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.


GIT-SVN(1)                        Git Manual                        GIT-SVN(1)

       git-svn - Bidirectional operation between a single Subversion branch
       and git

       git svn <command> [options] [arguments]

       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.

           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

           -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.

               Set the noMetadata option in the [svn-remote] config.

               Set the useSvmProps option in the [svn-remote] config.

               Set the useSvnsyncProps option in the [svn-remote] config.

               Set the rewriteRoot option in the [svn-remote] config.

               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.

               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

               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://address@hidden/project

               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 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

           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.

           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.

           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.

               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.

           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:

               is supported, non-numeric args are not: HEAD, NEXT, BASE, PREV,
               etc ...

               it´s not completely compatible with the --verbose output in svn
               log, but reasonably close.

               is NOT the same as --max-count, doesn´t count merged/excluded


           New features:

               shows the git commit sha1, as well

               our version of --pretty=oneline

               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
           Any other arguments are passed directly to git-log

           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.

               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.

           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.

           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

           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.

           Recursively finds and lists the svn:ignore property on directories.
           The output is suitable for appending to the $GIT_DIR/info/exclude

           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.

           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:

           Lists the properties stored in the Subversion repository about a
           given file or directory. Use -r/--revision to refer to a specific
           Subversion revision.

           Gets the Subversion property given as the first argument, for a
           file. A specific revision can be specified with -r/--revision.

           Shows the Subversion externals. Use -r/--revision to specify a
           specific revision.

           Only used with the init command. These are passed directly to

       -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

       -, --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.

           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 <address@hidden>

           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

           --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.

       -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"

           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

           config key: svn.followparent

       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.

           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.

       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 
           # 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

       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.

       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

           .ft C
           # Do the initial import on a server
                   ssh server "cd /pub && git svn clone 
           # Clone locally - make sure the refs/remotes/ space matches the 
                   mkdir project
                   cd project
                   git init
                   git remote add origin server:/pub/project
                   git config --add remote.origin.fetch 
                   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

       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.

       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).

       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.

       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.

       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 = 
                   tags = tags/*/project-a:refs/remotes/project-a/tags/*
                   trunk = trunk/project-a:refs/remotes/project-a/trunk

       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.


       Written by Eric Wong <address@hidden>.

       Written by Eric Wong <address@hidden>.

Git                       03/02/2009                        GIT-SVN(1)

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