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


    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
    fancy.

    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_
    driver.

    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
    users).

    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.

    Linus


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