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. Thierry
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