Re: Making Xorg easier to test (was Re: [git pull] drm request 3)

From: Linus Torvalds
Date: Fri Mar 05 2010 - 10:54:19 EST

On Fri, 5 Mar 2010, Carlos R. Mafra wrote:
> Whereas everytime I wanted to do that with Xorg it was such a pain that
> I want to keep away from that mess.

Actually, take it from me: Xorg is _pleasant_ to test these days.

Ok, so that's partly compared to the mess it _used_ to be, but it's really
night and day. The whole build system was so incredibly baroque and heavy
that you really had to understand it deeply if you wanted to do anything

And the non-fancy alternative was to just build the whole thing, which
took _hours_ even on fast machines because the build system overhead was
near-infinite (I dunno, maybe parallel builds could be made to work, but
it took more brain-power than I could ever put into it).

These days, there's a few dependencies you need to know about (I do agree
that from a user perspective the thing might have been made a bit _too_
modular) but they are generally fairly trivial, and there are scripts to
download all the drivers and misc utilities needed.

And the modularization often works: you can often (but by no means always;
it does require that the other parts are "close enough" and that there
haven't been any major changes) just have the source code to the one
driver you care about, and recompile and install just that _single_

I've done it. It's becautiful when it works. And it's a major pain when
you notice it didn't work, and you needed to get the whole server and
libdrm trees after all, and now you're not replacing single files any
more and have little idea what it will stomp on in your distro.

So it really is very convenient when it works. And X doesn't have
thousands of drivers like the kernel (maybe 10-15 that people care about
at all, and about three or four that actually really matter), and there
are seldom huge changes that affect them all, so the modularization
doesn't turn totally crazy.

So I can see where the Xorg people really like their new modular world. It
does work, it's _sooo_ much better than the mess it used to be, and the
problems are fairly manageable when they do happen.

The modular approach really works very well when there aren't lots of
interactions between the modules, and when the modules are few enough that
it isn't a total disaster (imagine doing a change that requires changes to
all drivers in Xorg, vs doing a change that requires changes to all
drivers in the kernel - the modular approach simply wouldn't work for the
latter case, because you'd spend all your time just chasing down external

That said, the _one_ thing I really wish could be done would be to make it
easier to install things side-by-side - and with the modularization, you
really do want to do it module-by-module. One of the things that makes it
so easy to test the kernel is that when you install one kernel, that
doesn't affect the others, and you can go back-and-forth in testing.
That's really important, because it makes testing trivial and non-scary
even in the presense of issues that makes the new version unusable.

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