[Qemu-devel] Switch to GIT. Why?

[Qemu-devel] Switch to GIT. Why?

[C.W. Betts]

Perhaps this has already been answered on the boards, but why was  
there a move to GIT?
The main reason why I ask is because I don't have GIT installed on my  
system.
Is it possible to set it up so that GIT has an SVN back-end?

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

[Erik de Castro Lopo]

C.W. Betts wrote:

> Perhaps this has already been answered on the boards, but why was  
> there a move to GIT?

I can't answer specifically for the Qemu case, but generally distributed
version control systems (DVCS) like git, bzr, hg, darcs etc are better for
distributed development than centralized systems like cvs and svn.

Above all, dvcs' are far better at handling and merging multiple branches.
I use svn at work, and I do realise that svn recently got much better at
merging between branches than it was, but it is still a poor cousin to
the others in this regard.

> The main reason why I ask is because I don't have GIT installed on my  
> system.

You're sending email using a Mac so this may be what you are
after:

    http://code.google.com/p/git-osx-installer/

On Debian/Ubuntu based Linux systems:

   apt-get install git

On Fedora Linux:

   yum install git

> Is it possible to set it up so that GIT has an SVN back-end?

Not that I know of.

Erik
-- 
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/

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

[M. Warner Losh]

In message: <20090426155257.7c6dac29.mle+tools@mega-nerd.com>
            Erik de Castro Lopo <mle+tools@mega-nerd.com> writes:
: C.W. Betts wrote:
: 
: > Perhaps this has already been answered on the boards, but why was  
: > there a move to GIT?
: 
: I can't answer specifically for the Qemu case, but generally distributed
: version control systems (DVCS) like git, bzr, hg, darcs etc are better for
: distributed development than centralized systems like cvs and svn.

They work better when the number of contributors is much greater than
the number of folks with write access to the repo.  They work about
the same when the numbers are about equal (although there are benefits
for the dvcs in this case too), modulo feature differences (eg perfoce
still blows the doors off all FOSS vcs systems for its branch merging
abilities, yet it is centralized).

: Above all, dvcs' are far better at handling and merging multiple branches.
: I use svn at work, and I do realise that svn recently got much better at
: merging between branches than it was, but it is still a poor cousin to
: the others in this regard.

At the expense, at least with hg and git, that you can't do subtree
checkouts.  You also lose the strict numbering that svn was giving us,
since both git and hg compute a hash of the tree and use that as a
revision number.  Usually this isn't a big deal, but something to be
aware of if you used to checkout sub-trees to do bug bisection...

: > The main reason why I ask is because I don't have GIT installed on my  
: > system.
: 
: You're sending email using a Mac so this may be what you are
: after:
: 
:     http://code.google.com/p/git-osx-installer/
: 
: On Debian/Ubuntu based Linux systems:
: 
:    apt-get install git
: 
: On Fedora Linux:
: 
:    yum install git

On FreeBSD:

cd /usr/ports/devel/git
make all install clean

or

portupgrade -P -N git

: > 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...

Warner

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

[Andreas Färber]

Hi,

Am 26.04.2009 um 07:28 schrieb C.W. Betts:

> Perhaps this has already been answered on the boards, but why was  
> there a move to GIT?
> The main reason why I ask is because I don't have GIT installed on  
> my system.
> Is it possible to set it up so that GIT has an SVN back-end?

On my Mac I simply compile Git from sources.
`git --help` doesn't work that way without major hackery[1] due to  
missing tools for the man pages, so I just look up the HTML  
documentation on the Web.

Subversion doesn't allow you to do local commits, for instance, which  
you'd need to create a series of dependent patches.

Andreas

[1] See Git's INSTALL file.

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

[Ralf Baechle]

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)

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

[Lennart Sorensen]

On Sun, Apr 26, 2009 at 01:13:20AM -0600, M. Warner Losh wrote:
> At the expense, at least with hg and git, that you can't do subtree
> checkouts.  You also lose the strict numbering that svn was giving us,
> since both git and hg compute a hash of the tree and use that as a
> revision number.  Usually this isn't a big deal, but something to be
> aware of if you used to checkout sub-trees to do bug bisection...

But of course that is part of why svn can't merge from one tree to
another without loosing the history and git can (and I suspect Hg can
as well).  So the strict numbering while it seems very useful, is actually
a problem in many cases.

-- 
Len Sorensen

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

[M. Warner Losh]

In message: <20090427131059.GT3795@csclub.uwaterloo.ca>
            lsorense@csclub.uwaterloo.ca (Lennart Sorensen) writes:
: On Sun, Apr 26, 2009 at 01:13:20AM -0600, M. Warner Losh wrote:
: > At the expense, at least with hg and git, that you can't do subtree
: > checkouts.  You also lose the strict numbering that svn was giving us,
: > since both git and hg compute a hash of the tree and use that as a
: > revision number.  Usually this isn't a big deal, but something to be
: > aware of if you used to checkout sub-trees to do bug bisection...
: 
: But of course that is part of why svn can't merge from one tree to
: another without loosing the history and git can (and I suspect Hg can
: as well).  So the strict numbering while it seems very useful, is actually
: a problem in many cases.

Yes.  And that's why you can only check out entire trees, and never
subtrees, with git and hg, but you can with svn.  git and hg force a
small view of the system to be its own repo.  So something the size of
X11 or FreeBSD could never use git or hg without breaking the
integrated tree model.  FreeBSD used svn to not break it because we
like the development model we have (and think Linus' talk at google
was very arrogant to suggest it was broken), while the X11 folks broke
their tree up into lots of modules, and got out of the making sure it
all worked together business (which makes integrating X11 into systems
harder now, alas).

For qemu, none of these issues are likely to be an issue, but it is
something to keep in mind...

Warner

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

[Lennart Sorensen]

On Mon, Apr 27, 2009 at 07:54:32AM -0600, M. Warner Losh wrote:
> Yes.  And that's why you can only check out entire trees, and never
> subtrees, with git and hg, but you can with svn.  git and hg force a
> small view of the system to be its own repo.  So something the size of
> X11 or FreeBSD could never use git or hg without breaking the
> integrated tree model.  FreeBSD used svn to not break it because we
> like the development model we have (and think Linus' talk at google
> was very arrogant to suggest it was broken), while the X11 folks broke
> their tree up into lots of modules, and got out of the making sure it
> all worked together business (which makes integrating X11 into systems
> harder now, alas).

It is certainly a tradeoff.  Of course with svn, when you do a checkout,
you get one version of the code.  If you want to search te history,
you have to talk to the server.  With git a "checkout" (clone) gets you
everything, history and all.  Makes searches and switching revisions
much faster, but makes the initial copy take much longer.

What X11 did also made it much easier to fix bugs, since you can now
work on the smaller pieces and release them much easier than you can
release the whole thing.  As for making sure it all works together,
I am not convinced it made it harder.  Seems development and such has
gotten much faster and better as a result.  It is no longer completely
overwhelming to work with.

> For qemu, none of these issues are likely to be an issue, but it is
> something to keep in mind...

True.  Of course as long as you have one tree per application, even
freebsd should be able to work with something like git.  Having one
giant tree for everything sounds nuts to me.  No idea how they do it
(I can't stand the userland of BSD in general, so I don't work with it.
Good applications, good kernel, lousy setup. :)  Debian kfreebsd may
change that of course.)

-- 
Len Sorensen

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

[M. Warner Losh]

In message: <20090427142237.GV3795@csclub.uwaterloo.ca>
            lsorense@csclub.uwaterloo.ca (Lennart Sorensen) writes:
: On Mon, Apr 27, 2009 at 07:54:32AM -0600, M. Warner Losh wrote:
: > Yes.  And that's why you can only check out entire trees, and never
: > subtrees, with git and hg, but you can with svn.  git and hg force a
: > small view of the system to be its own repo.  So something the size of
: > X11 or FreeBSD could never use git or hg without breaking the
: > integrated tree model.  FreeBSD used svn to not break it because we
: > like the development model we have (and think Linus' talk at google
: > was very arrogant to suggest it was broken), while the X11 folks broke
: > their tree up into lots of modules, and got out of the making sure it
: > all worked together business (which makes integrating X11 into systems
: > harder now, alas).
: 
: It is certainly a tradeoff.  Of course with svn, when you do a checkout,
: you get one version of the code.  If you want to search te history,
: you have to talk to the server.  With git a "checkout" (clone) gets you
: everything, history and all.  Makes searches and switching revisions
: much faster, but makes the initial copy take much longer.
: 
: What X11 did also made it much easier to fix bugs, since you can now
: work on the smaller pieces and release them much easier than you can
: release the whole thing.  As for making sure it all works together,
: I am not convinced it made it harder.  Seems development and such has
: gotten much faster and better as a result.  It is no longer completely
: overwhelming to work with.

Heh, it never seemed overwhelming to me when I worked on it...

: > For qemu, none of these issues are likely to be an issue, but it is
: > something to keep in mind...
: 
: True.  Of course as long as you have one tree per application, even
: freebsd should be able to work with something like git.  Having one
: giant tree for everything sounds nuts to me.  No idea how they do it
: (I can't stand the userland of BSD in general, so I don't work with it.
: Good applications, good kernel, lousy setup. :)  Debian kfreebsd may
: change that of course.)

One big tree works very well.  One command builds the whole thing so
updates are easy, but you can still go to a specific directory and
just build that if you find a bug in ls.  Things are stable enough
that it is rare you'd want to just update one thing for a critical bug
fix.

It actually works very well and eliminates the version dependency
problems you run into if you are using/building linux packages of
whatever flavor...

Warner