Re: Why we should avoid new submodules if possible

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 28, 2022 at 12:50:06PM +0200, Thomas Huth wrote:
> On 28/06/2022 12.30, 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.
> > 
> > But of course if you do you do not get updates ;) You do
> > however rely on a 3rd party to faithfully provide you
> > correct code based on the version, and host it forever.
> > 
> > > 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
> > 
> > how is pip better?
> 
> You don't end up with an inconsistent source tree in that case (which
> happens with submodules quite easily, at least for me it happened a couple
> of times already). Either the machine has an internet connection, so that
> pip can install the missing bits, or it does not and the test has to be
> skipped.

skipped tests are too easy to ignore ...

> But if I copy the wrong state of a submodule around, things get
> messed up quite easily in my experience. Ok, you could say that this is just
> my special setup with rsync, but already given the fact that "git checkout"
> creates an inconsistent state of your source tree until you run the script
> for updating the submodules the next time is an indication that submodules
> are rather a shaky thing (e.g. if you'd create a tarball for somebody else
> from your source tree right after doing a "git checkout").

yea one has to remember to set submodule.recurse = true in .gitconfig

I agree it's annoying, I guess they don't change it for compat reasons.


> > > - 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.
> > 
> > how is pip better here?
> 
> You don't get incomplete/non-working tarballs in that case.

So skip the test ;)

> > > - 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?
> > 
> > I think we can skip the checkout in the tarball if we like.
> > If people want to run the test they can checkout then.
> 
> Release tarballs don't include the ".git" folder infrastructur, so everybody
> who downloads a tarball will simply never be able to run the test.

I actually think I'm fine with that for this specific case.

> > 
> > > - 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.
> > 
> > Come on, this is just a test. We *really* don't care if an ISO
> > we use to test ACPI is using an exploitable version of grub.
> 
> Wait, I thought we were only talking about tappy here? The ISO binaries
> should certainly *not* be bundled in the QEMU tarballs (they are too big
> already anyway, we should rather think of moving the firmware binaries out
> of the tarball instead).
> 
>  Thomas

IIUC there are three things we are discussing
- biosbits source
- biosbits image
- tappy


-- 
MST