Re: Is cp -al safe with git?

[Junio C Hamano <junkio@cox.net>]

Johannes Sixt <johannes.sixt@telecom.at> writes:

> For one reason or another I would like to "clone" a local repo including the
> checked-out working tree with cp -al instead of cg-clone/git-clone, i.e.
> have all files hard-linked instead of copied.
>
> Can the copies be worked on independently without interference (with the git
> tool set)?
>
> One thing I noticed is that git-reset or probably git-checkout-index breaks
> links of files that need not be changed by the reset. Example:
>
> # make 2 files, commit
> $ mkdir orig && cd orig
> $ git-init-db 
> defaulting to local storage area
> $ echo foo > a && cp a b && git-add a b && git-commit -a -m 1
> Committing initial tree 99b876dbe094cb7d3850f1abe12b4c5426bb63ea
>
> # 2nd commit modifies only one file:
> $ echo bar > a && git-commit -a -m 2
>
> # create the copy:
> $ cd ..
> $ cp -al orig copy
> $ cd copy
>
> # working files are hard-linked:
> $ ls -l
> total 8
> -rw-r--r-- 2 jsixt users 4 Nov 16 19:24 a
> -rw-r--r-- 2 jsixt users 4 Nov 16 19:23 b
>
> # nuke a commit:
> $ git-reset --hard HEAD^
> $ ls -l
> total 8
> -rw-r--r-- 1 jsixt users 4 Nov 16 19:24 a
> -rw-r--r-- 1 jsixt users 4 Nov 16 19:24 b
>
> I'd have expected that the hard-link of b remained and only a's link were
> broken. Does it mean that git-reset writes every single file also for large
> trees like the kernel? I cannot believe this. Can someone scratch the
> tomatoes off my eyes please?

Most likely you didn't run "update-index --refresh" after "cp -l"?
Not just in the new copied repository but in the original
repository I would suspect you would see this.  This is because
the index caches ctime and making a new hardlink manipulates the
files' inodes, thus making the cached information stale.