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 limiting who does releases would be sufficient. Unless there is > someone with enough free time and energy to volunteer to be libdrm > maintainer. > > But tbh I don't think it has been too much of a problem in the past. > I'm not sure if I actually read somewhere the rule about not updating > kernel headers until the interface is locked in (ie. drm-next), but it > seemed like common sense to me. Could be enough just to document this > a bit more explicitly. It's not something I feel very strongly about. People seemed unhappy about the current state of affairs, so I thought I'd dump a few ideas. =) Thierry
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