[Buildroot] [PATCH 1/2] git: fix handling of git repos using master as version

Bob Beckett bbeckett at netvu.org.uk
Mon Jun 4 16:32:41 UTC 2018

Thanks for the more in depth explanation.

I agree with all of the reasons outlined for the purpose of being purely a
reproducible build manager, which buildroot only ever aimed to be.

However, people do use it during development, and with a reasonably large
number of custom packages all in development at the same time, using the
_OVERRIDE_SRCDIR method to test latest versions of multiple packages
becomes very unwieldy.
My solution so far has been to point the version at the branch that active
development is taking place on, and removing the build directories and
packages for the specific projects each time.
When I am not the one doing the development on each package's source, but
am developing the rootfs, this means I dont have to manually keep updating
my local git repositories for each project.
Once each package has hit their first release version, they do get tagged
and the release branch for the project's BR2_EXTERNAL directory gets
updated with those versions, and each version thereafter, but the
development branch for the external directory persistently stays on the
development branch head for each package.

Regarding not knowing the sha before a checkout, would git ls-remote not
suffice for this? e.g.

$ git ls-remote git at gitlab.com:adhlinux/buildroot/buildroot.git master
407fb2fe202aaeb273e4986dc88c30596a7fe8db    refs/heads/master
407fb2fe202aaeb273e4986dc88c30596a7fe8db    refs/remotes/upstream/master

It would allow you to check for changes in sha without doing a new fetch.

Oh well, not to worry. Ill keep it as a local patch, as I suspect I am
treading old ground of "buildroot is not a development platform" (Ive seen
this discussion come up multiple times before).



On Mon, Jun 4, 2018 at 4:44 PM, Yann E. MORIN <yann.morin.1998 at free.fr>

> On 2018-06-04 15:59 +0100, Bob Beckett spake thusly:
> > Is this philosophy set in stone? I can conceive of useful situations
> where branches are preferable.
> The problem, as Thomas quickly explained, is that it does not behave as
> users expect.
> First, Buildroot creates a local tarball of the git reository. We do
> that for various reasons, one beiong to be able to prepare the
> compliance archive (make legal-info).
> So, if you run "make clean; make" then the local archive already exists
> and Buildroot will not download it again, i.e. it will nt update your
> git tree.
> Now, if you run "make distclean", then yes, it removes the download
> directory that you get in "buildroot/dl/", and so you will re-download
> again, and that will be the new branch you'll get.
> However, it is possible to override the download location, if you export
> BR2_DL_DIR in the environment, to tell Buildroot where to look for, and
> store new downloads, as a way to cache downloads for those users behind
> slow connections (not everyone has ADSL-class connection, even less so
> gigabit-class fibers). If BR2_DL_DIR is set, then Buildroot will never
> remove it, even with "make distclean". So, you're back to square one,
> where the local tarball still represent an old state of your branch.
> Ergo, it does not behave as you would think it would.
> The second problem, is that using a branch name makes the build
> non-reproducible.
> Today, you'll get a set of source from your branch, but maybe tomorrow
> it will point to something else, or even have disapeared (which is the
> least problematic issue, because the build would obviously fail, while
> it could succeed and result in a flawed state with a new branch).
> Ergo, it does not behave as you would think it would.
> So, using a branch name is flawed in two ways. We can't add support for
> using branch names in any reliable and predictable manner.
> > During large projects, where the rootfs is being developed at the same
> time as some custom packages,
> > it is quite useful to have a branch as the target. Usually, I just do a
> dirclean and delete the tar when I know
> > something has changed.
> >
> > If you wanted to make it more predictable, then maybe name the tar based
> on the version (branch name in this case) plus the sha,
> But we can't know the sha1 before we git checkout the branch, so we
> don;t know if we already have it localy, so we don;t know we can use a
> cached version, so this undermines the very reason to have a local cache
> to start with...
> > this way new tar packages would be created if the branch advances and
> also if a tag (or other supported refspec) changes via a
> > rebase etc.
> Changing a tag is bad. Repeat after me: changing a tag is bad! ;-)
> Yes, git allows that. Guns also allow one to shoot in ones' own foot.
> That does not mean this is a good idea... ;-p
> > The particular thing I like to avoid is multiple version bumps in the
> package spec and tags in the package source repos during
> > development. When many people are working on package project, expecting
> them all to take time to publish tags for every little
> > change gets unrealistic.
> >
> > The question I would ask is is there any harm in supporting that if it
> can be done reliably and predictably?
> > Anyway, if this design is locked down, then I will just maintain this
> patch locally for us to use :)
> And as I hope I clearly explained above, there is no wau to make it work
> predictably and reliably.
> Regards,
> Yann E. MORIN.
> > Thanks
> >
> > Bob
> > On Mon, Jun 4, 2018 at 3:33 PM, Thomas Petazzoni < [1]
> thomas.petazzoni at bootlin.com> wrote:
> >
> >   Hello,
> >   On Mon,  4 Jun 2018 14:32:29 +0100, Robert Beckett wrote:
> >   > Since changing to git init followed by fetch to initialise
> >   > git cache, when using master branch as the target version
> >   > for a package, git refuses to fetch in to currently checkout
> >   > out branch or master.
> >
> >   I think we don't want to support using branches as Git versions, as it
> >   doesn't make sense, because it won't behave as the user expects.
> >
> >   If you use a branch as _VERSION for a package, Buildroot will only
> >   download once, and never update to newer commits in this branch,
> >   because it will already have a cached tarball in its DL_DIR.
> >
> >   So I'm not sure we want to add some code to support a use case that we
> >   don't want support :-)
> >   Thomas
> >   --
> >   Thomas Petazzoni, CTO, Bootlin (formerly Free Electrons)
> >   Embedded Linux and Kernel engineering
> >   [2]https://bootlin.com
> >
> > Links:
> > 1. mailto:thomas.petazzoni at bootlin.com
> > 2. https://bootlin.com
> --
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