Re: [RFC PATCH] repack: rewrite the shell script in C.

From: Stefan Beller <stefanbeller@googlemail.com>
Date: Aug 15, 2013, 07:46 UTC
Message-ID: <520C873A.9070900@googlemail.com>
In-Reply-To: <201308141725.43127.mfick@codeaurora.org>

On 08/15/2013 01:25 AM, Martin Fick wrote:

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> On Wednesday, August 14, 2013 04:51:14 pm Matthieu Moy 
> wrote:
>> Antoine Pelisse <apelisse@gmail.com> writes:
>>> On Wed, Aug 14, 2013 at 6:27 PM, Stefan Beller
>>>
>>> <stefanbeller@googlemail.com> wrote:
>>>>  builtin/repack.c               | 410
>>>>  +++++++++++++++++++++++++++++++++++++++++
>>>>  contrib/examples/git-repack.sh | 194
>>>>  +++++++++++++++++++ git-repack.sh                  |
>>>>  194 -------------------
>>>
>>> I'm still not sure I understand the trade-off here.
>>>
>>> Most of what git-repack does is compute some file
>>> paths, (re)move those files and call git-pack-objects,
>>> and potentially git-prune-packed and
>>> git-update-server-info.
>>> Maybe I'm wrong, but I have the feeling that the
>>> correct tool for that is Shell, rather than C (and I
>>> think the code looks less intuitive in C for that
>>> matter).
>>
>> There's a real problem with git-repack being shell (I
>> already mentionned it in the previous thread about the
>> rewrite): it creates dependencies on a few external
>> binaries, and a restricted server may not have them. I
>> have this issue on a fusionforge server where Git repos
>> are accessed in a chroot with very few commands
>> available: everything went OK until the first project
>> grew enough to require a "git gc --auto", and then it
>> stopped accepting pushes for that project.
>>
>> I tracked down the origin of the problem and the
>> sysadmins disabled auto-gc, but that's not a very
>> satisfactory solution.
>>
>> C is rather painfull to write, but as a sysadmin, drop
>> the binary on your server and it just works. That's
>> really important. AFAIK, git-repack is the only
>> remaining shell part on the server, and it's rather
>> small. I'd really love to see it disapear.
> 
> I didn't review the proposed C version, but how was it 
> planning on removing the dependencies on these binaries?  
> Was it planning to reimplement mv, cp, find?

These small programms (at least mv and cp) are just convenient interfaces for system calls from within the shell. You can use these system calls to achieve a similar results compared to the commandline option. http://linux.die.net/man/2/rename http://linux.die.net/man/2/unlink

> Were there 
> other binaries that were problematic that you were thinking 
> of?  From what I can tell it also uses test, mkdir, sed, 
> chmod and naturally sh, that is 8 dependencies.

mkdir, test, chmod are also easily done via system calls. The system calls are usually capsulated by the libc to have an easy C interface. (A standard C function call)

sed and find are tricky indeed, but you can get around it with a few lines of C (maybe 10?) for each occurrence. We don't need the full power of sed and find, but rather only the exact specific matching regexp.

 If those

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> can't be depended upon for existing, perhaps git should just 
> consider bundling busy-box or some other limited shell 
> utils, or yikes!, even its own reimplementation of these 
> instead of implementing these independently inside other git 
> programs?
>

The C version as of now has twice the lines of code than the shell version. And I am pretty sure I did some rookie mistakes, so the code can be down-sized by better use of already existing functions. So I guess the final version will have less lines than in the proposed patch as of now.