Re: Why we should avoid new submodules if possible

[Warner Losh <imp@bsdimp.com>]

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On Wed, Sep 28, 2022 at 7:09 AM Daniel P. Berrangé <berrange@redhat.com>
wrote:

> On Wed, Sep 28, 2022 at 05:53:17AM -0400, Michael S. Tsirkin wrote:
> > On Wed, Sep 28, 2022 at 10:37:14AM +0100, Daniel P. Berrangé wrote:
> > > On Wed, Sep 28, 2022 at 05:26:42AM -0400, Michael S. Tsirkin wrote:
> > > > On Tue, Jun 28, 2022 at 12:21:39PM +0200, Thomas Huth wrote:
> > > > > On 28/06/2022 12.03, Michael S. Tsirkin wrote:
> > > > > [...]
> > > > > > For biosbits if we are going this route then I feel a submodule
> is much
> > > > > > better.  It records which version exactly each qemu version
> wants.
> > > > >
> > > > > As far as I know, you can also specify the version when using pip,
> can't
> > > > > you? So that's not really an advantage here.
> > > > >
> > > > > On the contrary, submodules have a couple of disadvantages that I
> really
> > > > > dislike:
> > > > >
> > > > > - submodules do not get updated automatically when doing a "git
> checkout",
> > > > > we have to update them via a script instead. This causes e.g.
> trouble if you
> > > > > rsync your source tree to a machine that has no access to the
> internet and
> > > > > you forgot to update the submodule before the sync
> > > > >
> > > > > - the content of submodules is not added to the tarballs that get
> created on
> > > > > the git forges automatically. There were lots of requests from
> users in the
> > > > > past that tried to download a tarball from github and then
> wondered why they
> > > > > couldn't compile QEMU.
> > > > >
> > > > > - we include the submodule content in our release tarballs, so
> people get
> > > > > the impression that hte submodule content is part of the QEMU
> sources. This
> > > > > has two disadvantages:
> > > > >  * We already got bug reports for the code in the submodule,
> > > > >    where people did not understand that they should report that
> > > > >    rather to the original project instead (i.e. you ship it - you
> > > > >    own it)
> > > > >  * People get the impression that QEMU is a huge monster
> > > > >    application if they count the number of code lines, run
> > > > >    their code scanner tools on the tarball contents, etc.
> > > > >    Remember "nemu", for example, where one of the main complaints
> > > > >    was that QEMU has too many lines of code?
> > > > >
> > > > > - If programs includes code via submodules, this gets a higher
> > > > >   burder for distro maintainers, since they have to patch each
> > > > >   and every package when there is a bug, instead of being able to
> > > > >   fix it in one central place.
> > > > >
> > > > > So in my opinion we should avoid new submodules if there is an
> alternative.
> > > > >
> > > > >  Thomas
> > > >
> > > > So looking at the latest proposals downloading files from CI,
> > > > checksumming them etc etc. No auto checkout, not added automatically
> > > > either, right?
> > > >
> > > > This seems to be the only difference:
> > > > - we include the submodule content in our release tarballs
> > >
> > > That's just one of the issues with submodules. Working with them in
> general
> > > is not a pleasant experiance.
> >
> > This is what I asked about at the maintainers summit.
> > I'd like to map the issues and see if there's anything
> > we can do to solve them. In particular we will likely
> > keep using submodules where we historically did
> > so it's time well spent.
> >
> > I agree generally but the big question is what to replace these with.
> > Below I assume the replacement is a script such as avocado or pytest
> > with its own hashing, calling wget internally etc etc.
> >
> >
> > > Thomas pointed out some of the issues, such
> > > as 'git checkout' ignoring submodules, requiring extra steps to sync
> them.
> >
> >
> > Not different from a home grown SCM as part of test script, right?
>
> We're not building a home grown SCM as part of a test script, so
> this answer is irrelevant.
>
> > > There's also the perenial problem that developers frequently send
> > > patches that mistakenly include submodule changes,
> >
> > OK, so the thing to do would be to look for ways to exclude submodule
> changes
> > from git commits.
>
> If someone wants to make git suck less with submodules great, but needs
> someone to actually do the work.
>

A big part of the problem is knowing which of the following commands I have
to
do to undo the uncommitted changes, the committed changes, the staged
changes,
etc:

git submodule update --init --recursive
git submodule update --init
git submodule foreach --recursive git reset --hard
git submodule foreach --recursive git clean -xfd
git submodule foreach --recursive git clean -xfg

(all of these are in my history, I honestly don't know the difference
between the last two).
And each 'oops' takes time away from upstreaming bsd-user I don't really
have that
much of. I've wasted hours on this over the past year between all the
different ways
it can screw up.

To be fair, it is a relatively small fraction of the time, but as you can
tell from the
animation in my email it inspires much passion.

Warner


> > > I'd really like to see us doing more to eliminate as much use of
> submodules
> > > as is possible over time.p
> >
> > Or try to fix the problems, right?
>
> Again needs someone to actually make it happen.
>
> Meanwhile  QEMU already has an integrated test harness in the form
> of Avocado that does everything needed. If Avocado had just been
> used for this biosbits test in the first place, the test would
> likely have already been merged to QEMU, instead of us having this
> never ending debate on how to re-invent an alternative to what
> already avocado does.
>
> With regards,
> Daniel
> --
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>
>

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