Re: [3/4] What's not in 1.5.2 (new topics)

From: Josef Weidendorfer <josef.weidendorfer@gmx.de>
Date: May 17, 2007, 23:41 UTC
Message-ID: <200705180141.06862.Josef.Weidendorfer@gmx.de>
In-Reply-To: <20070517215841.GB29259@mellanox.co.il>

On Thursday 17 May 2007, Michael S. Tsirkin wrote:

Show 33 quoted lines

> > What I was "handwaving" (or "envisioning") was to have something
> > like this in .gitmodules:
> > 
> > 	[subproject "kernel/"]
> >         	URL = git://git.kernel.org/pub/linux-2.4.git
> > 
> > (or 2.6, depending on the revision of the superproject) and per
> > repository configuration would maps this with these two entries:
> > 
> > 	[subproject "git://git.kernel.org/pub/linux-2.4.git"]
> >         	URL = http://www.kernel.org/pub/linux-2.4.git
> > 
> > 	[subproject "git://git.kernel.org/pub/linux-2.6.git"]
> >         	URL = http://www.kernel.org/pub/linux-2.6.git
> > 
> > The intent is 
> > 
> > 	(1) "kernel/" directory is found to be a gitlink in the
> >             tree/index; .gitmodules is consulted to find the
> >             "URL", which is just a handle and the initial hint
> > 
> > 	(2) That "initial hint" is used to look up the
> >             subproject entry from the configuration, to find the
> >             "real" URL that is used by this repository
> 
> I'm reading up on submodules, two questions on this:
> 
> 1. I understand the usefulness of the hint for public repositories, (the user might
> need help discovering where to get submodules) but for private ones would this
> create a hassle: I start with a subproject in ~/subprojecttest and if that gets
> put in the URL hint, I have to maintain a map for ~/subprojecttest in my
> .git/config forever even after I move it to ~/subprojectproduction, just to make
> old releases build?

Yes, AFAICS that was the original idea; but that is no problem as we will need an override scheme.

However, I think the usage of "url"/"url hint" as the 1st level subproject identifier really is badly misleading and confusing for users; it would be better for this identifier to not look like a URL at all. But by naming it "url" in .gitmodules, the user is tempted to put an URL at this place.

IMHO it is by far better to simply talk about the "subproject name/identifier" which is valid in the subproject namespace of the superproject.

And why not use the .gitattributes for the ".gitmodules" needs? With linux 2.4 as subproject in "top/kernel/", there could be a "top/.gitattributes" with

 kernel subproject=linux24

We could have a default rule that in the absense of the attribute, we default to the path of the submodule, ie. to

 kernel subproject=top/kernel

In .git/config, there needs to be a config entry like

	[subproject "linux24"]
		URL = http://www.kernel.org/pub/linux-2.4.git

Again, we could have a default URL in the absence of this config entry which is relative to the URL of the superproject, and which allows for the superproject repository to act as proxy.

As relative path I would propose $SUPERURL/subproject/$SUBPROJECTNAME, ie. if the superproject is at git://git.kernel.org/pub/super.git, the above subproject would default to the URL git://git.kernel.org/pub/super.git/subproject/linux24 which could be a symlink on the server.

To support different subproject repositories linked in at the same path of a superproject, Nicolas noted that we would have to replace the subproject repository at top/kernel/.git (taking my example above) whenever we cross the subproject change boundary in a checkout (e.g. from linux24 to linux26). The natural thing here would be to have subproject repositories at a seperate place, like inside of the superproject repository such as at ".git/subproject/linux24", which works well with my default interpretation of relative subproject paths above. At checkout, the correct repository would be bound by a symlink:

 top/kernel/.git -> .git/subproject/linux24

Instead of a symlink, a magically working linkage mechanisms would be better (the .git/gitlink proposal).

Show 7 quoted lines

> 2. Suppose .gitmodules in upstream tree points at subproject repo at kernel.org,
> and I clone from there - my repo will point at kernel.org by default?
> But now, I'd like everyone who clones from *my* repo to get
> pointed at *my* server by default (e.g. for mirroring),
> but would not changing .gitmodules create a commit so my
> head will now differ from upstream  - so it won't be signed properly etc...
> Did I misunderstand something?

No, that is correct. Supporting a relative URL specification as proposed above should solve this issue.

Josef