Re: Kernel SCM saga..

Linus Torvalds
2005-04-08T15:48:52Z

On Fri, 8 Apr 2005 ross@jose.lug.udel.edu wrote:
>
> Here's a partial solution. It does depend on a modified version of
> cat-file that behaves like cat. I found it easier to have cat-file
> just dump the object indicated on stdout. Trivial patch for that is included.

Your trivial patch is trivially incorrect, though. First off, some files
may be binary (and definitely are - the "tree" type object contains
pathnames, and in order to avoid having to worry about special characters
they are NUL-terminated), and your modified "cat-file" breaks that.

Secondly, it doesn't check or print the tag.

That said, I think I agree with your concern, and cat-file should not use
a temp-file. I'll fix it, but I'll also make it verify the tag (so you'd
now have to know the tag in advance if you want to cat the data).

Something like

cat-file -t <sha1> # output the tag
cat-file <tag> <sha1> # output the data

or similar. Easy enough. That way you can do

torvalds@ppc970:~/git> ./cat-file -t `cat .dircache/HEAD `
commit

and

torvalds@ppc970:~/git> ./cat-file commit `cat .dircache/HEAD `

tree ca30cdf8df2f31545cc1f2c1be62619111b6f6aa
parent c2474b336d7a96fb4e03e65d229bcddc62b244fc
author Linus Torvalds <torvalds@ppc970.osdl.org> Fri Apr 8 08:16:38 2005
committer Linus Torvalds <torvalds@ppc970.osdl.org> Fri Apr 8 08:16:38 2005

Make "cat-file" output the file contents to stdout.

New syntax: "cat-file -t <sha1>" shows the tag, while "cat-file <tag> <sha1>"
outputs the file contents after checking that the supplied tag matches.

I'll rsync the .dircache directory to kernel.org. You'll need to update
your scripts.

> Now to see what I come up with for commit, push, and pull...

A "commit" (*) looks roughly like this:

# check with "show-diff" what has changed, and check if
# you need to add any files..

update-cache

# check with "show-diff" that it all looks right

oldhead=$(cat .dircache/HEAD)
newhead=$(commit-tree $(write-tree) -p $oldhead < commit-message)

# update the head information
if [ "$newhead" != "" ] ; then echo $newhead > .dircache/HEAD; fi

(*) I call this "commit", but it's really something much simpler. It's
really just a "I now have <this directory state>, I got here from
<collection of previous directory states> and the reason was <reason>".

The "push" I use is

rsync -avz --exclude index .dircache/ <destination-dir>

and you can pull the same way, except when you pull you should save _your_
HEAD file first (and then you're screed. There's no way to merge. If
you've made changes and committed them, your changes are still there, but
they are now on a different HEAD than the new one).

That, btw, is kind of the design. "git" really doesn't care about things
like merges. You can use _any_ SCM to do a merge. What "git" does is track
directory state (and how you got to that state), and nothing else. It
doesn't merge, it doesn't really do a whole lot of _anything_.

So when you "pull" or "push" on a git archive, you get the "union" of all
directory states in the destination. The HEAD thing is _one_ pointer into
the "sea of directory states", but you really have to use something else
to merge two directory states together.

Linus