On Thu, Oct 9, 2014 at 3:54 AM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: > On Thu, Oct 09, 2014 at 03:32:26AM -0400, Rob Clark wrote: >> On Wed, Oct 8, 2014 at 12:00 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: >> > >> > So idea is simple, each ioctl would use some struct like : >> > >> > struct radeon_ioctl { >> > u32 version; >> > u32 size; >> > }; >> >> >> fwiw, drm_ioctl() will do the right thing (zero-pad) for growing >> ioctls these days.. > > It's more about userspace knowing about ioctl XY and having a way > to override/ask for special version of each ioctl. So if we screw > ioctl XY, we can add a new version to XY and we can try to work > around if userspace still request the old version. It is mostly > about trying to keep the code clean and avoiding things like the > chunk stuff of the cs ioctl. > > For instance if you cs ioctl with the following struct as ioctl > parameter: > > struct drm_radeon_cs_ioctl_version_00 { > u64 *cs; > u32 size; > u32 flags; > }; > > And now you have a new generation of hardware or are just adding > a new feature : > > struct drm_radeon_cs_ioctl_version_01 { > u64 *cs; > u32 size; > u32 flags; > u32 newfeature fields; > }; > > Of course you can argue that you could use the size of user space > paremeter to do this simple example. But with versioning you can > also move fields around, remove fields, ... basicly it is just more > flexible with small overhead of having one more indirection but this > will be lost into the ioctl cost anyway (i highly doubt it would > turns as a bottleneck). sure, explicit version is more flexible (and I don't even think you need an extra layer of indirection for that).. just pointing out that we do have a way to grow ioctls now (with the constraint that zero's is a sane backwards compat value for the new field(s)) BR, -R > > Cheers, > Jérôme > >> >> BR, >> -R _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel