Re: [Mesa-dev] rules for merging patches to libdrm

[Jerome Glisse <j.glisse@gmail.com>]

On Mon, Nov 18, 2013 at 05:41:50PM +0100, Thierry Reding wrote:
> On Mon, Nov 18, 2013 at 11:21:36AM -0500, Rob Clark wrote:
> > On Mon, Nov 18, 2013 at 10:23 AM, Thierry Reding
> > <thierry.reding@gmail.com> wrote:
> > > On Mon, Nov 18, 2013 at 10:17:47AM -0500, Rob Clark wrote:
> > >> On Mon, Nov 18, 2013 at 8:29 AM, Thierry Reding
> > >> <thierry.reding@gmail.com> wrote:
> > >> > On Sat, Nov 09, 2013 at 01:26:24PM -0800, Ian Romanick wrote:
> > >> >> On 11/09/2013 12:11 AM, Dave Airlie wrote:
> > >> >> >>> How does this interact with the rule that kernel interfaces require an
> > >> >> >>> open source userspace? Is "here are the mesa/libdrm patches that use
> > >> >> >>> it" sufficient to get the kernel interface merged?
> > >> >> >>
> > >> >> >> That's my understanding: open source userspace needs to exist, but it
> > >> >> >> doesn't need to be merged upstream yet.
> > >> >> >
> > >> >> > Having an opensource userspace and having it committed to a final repo
> > >> >> > are different things, as Daniel said patches on the mesa-list were
> > >> >> > sufficient, they're was no hurry to merge them considering a kernel
> > >> >> > release with the code wasn't close, esp with a 3 month release window
> > >> >> > if the kernel merge window is close to that anyways.
> > >> >> >
> > >> >> >>> libdrm is easy to change and its releases are cheap. What problem does
> > >> >> >>> committing code that uses an in-progress kernel interface to libdrm
> > >> >> >>> cause? I guess I'm not understanding something.
> > >> >> >>
> > >> >> >
> > >> >> > Releases are cheap, but ABI breaks aren't so you can't just go release
> > >> >> > a libdrm with an ABI for mesa then decide later it was a bad plan.
> > >> >> >
> > >> >> >> Introducing new kernel API usually involves assigning numbers for things
> > >> >> >> - a new ioctl number, new #defines for bitfield members, and so on.
> > >> >> >>
> > >> >> >> Multiple patches can be in flight at the same time.  For example, Abdiel
> > >> >> >> and I both defined execbuf2 flags:
> > >> >> >>
> > >> >> >> #define I915_EXEC_RS (1 << 13)     (Abdiel's code)
> > >> >> >> #define I915_EXEC_OA (1 << 13)     (my code)
> > >> >> >>
> > >> >> >> These obviously conflict.  One of the two will land, and the second
> > >> >> >> patch author will need to switch to (1 << 14) and resubmit.
> > >> >> >>
> > >> >> >> If we both decide to push to libdrm, we might get the order backwards,
> > >> >> >> or maybe one series won't get pushed at all (in this case, I'm planning
> > >> >> >> to drop my patch).  Waiting until one lands in the kernel avoids that
> > >> >> >> problem.  Normally, I believe we copy the kernel headers to userspace
> > >> >> >> and fix them up a bit.
> > >> >> >>
> > >> >> >> Dave may have other reasons; this is just the one I thought of.
> > >> >> >
> > >> >> > But mostly this, we've been stung by this exact thing happening
> > >> >> > before, and we made the process to stop it from happening again.
> > >> >>
> > >> >> Then in all honestly, commits to libdrm should be controlled by either a
> > >> >> single person or a small cabal... just like the kernel and the xserver.
> > >> >>  We're clearly in an uncomfortable middle area where we have a stringent
> > >> >> set of restrictions but no way to actually enforce them.
> > >> >
> > >> > That doesn't sound like a bad idea at all. It obviously causes more work
> > >> > for whoever will be the gatekeeper(s).
> > >> >
> > >> > It seems to me that libdrm is currently more of a free-for-all type of
> > >> > project, and whoever merges some new feature required for a particular X
> > >> > or Mesa driver cuts a new release so that the version number can be used
> > >> > to track the dependency.
> > >> >
> > >> > I wonder if perhaps tying the libdrm releases more tightly to Linux
> > >> > kernel releases would help. Since there already is a requirement for new
> > >> > kernel APIs to be merged before the libdrm equivalent can be merged,
> > >> > then having both release cycles in lockstep makes some sense.
> > >>
> > >> Not sure about strictly tying it to kernel releases would be ideal.
> > >> Not *everything* in libdrm is about new kernel APIs.  It tends to be
> > >> the place for things needed both by xorg ddx and mesa driver, which I
> > >> suppose is why it ends up a bit of a free-for-all.
> > >
> > > I didn't mean that every release would need to be tied to the Linux
> > > kernel. But whenever a new Linux kernel release was made, relevant
> > > changes from the public headers could be pulled into libdrm and a
> > > release be made. I could even imagine a matching of version numbers.
> > > libdrm releases could be numbered using the same major and minor as
> > > Linux kernels that they support. Micro version numbers could be used
> > > in intermediate releases.
> > 
> > maybe an update-kernel-headers.sh script to grab the headers from
> > drm-next and update libdrm wouldn't be a bad idea?
> 
> Perhaps. But I think it could even be a manual step. It's not something
> that one person should be doing alone, but rather something that driver
> maintainers should be doing, since they know best what will be needed
> in a new version of libdrm.
> 
> Like I mentioned in another subthread, I think a subtree-oriented model
> could work well.
> 
> Thierry

Please stop asking for more process bureaucracy. libdrm development model
works fine. Everyone is free to commit and release when needed. The recent
hickup is just that a hickup and does not warrant any changes.

Jerome