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@xxxxxxxxx> 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@xxxxxxxxx> 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
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