On Mon, Nov 18, 2013 at 05:30:34PM +0100, Maarten Lankhorst wrote: > op 09-11-13 22:26, Ian Romanick schreef: > > 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. > > Most of libdrm is hardware specific, so by necessity it is developed like that. Most of the Linux kernel is hardware specific, yet it is developed differently. > I don't think robclark will touch libdrm/intel for example. Certainly a subtree-oriented development model could work well for libdrm. What I mean is that not a single person (or even a set of people) would need to pick patches from a mailing list, but driver maintainers could have separate trees which can be merged into the upstream tree. That could potentially lower the workload on the libdrm maintainer(s). > I do not think explicit control is needed, just be more careful and don't cause > unnecessary headaches by committing code to libdrm before it's in a upstream kernel. > Preferably wait until it appears in torvalds/linux.git, but it seems airlied has a > lower standard. :) > > Sometimes software bugs might warrant a release too, so this middle area is needed. Having a different development model doesn't exclude the possibility for bugfix releases. Neither does explicit control of what patches are merged. Thierry
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