dri: Epoch how no-error context creation works
The bug here is that the DRI context "flags" are intended to alias the
GLX context flag values, and they don't, DRI's no-error flag is GLX's
reset-isolation flag. GLX (and EGL!) treat no-error as a context
attribute, and reset isolation predates Mesa's no-error implementation
by several years. The GL_KHR_no_error
spec does describe it as a
"context flag", though, so maybe that's why we do it as a (DRI) context
flag.
In order to unalias these we need a new contract with the driver. The
loaders will now only expose the winsys no-error extension if the driver
exposes __DRI2_NO_ERROR2
, and the drivers now only expose that and not
the old one. This new extension is a promise to expect no-error-ness as
a context attribute, matching the GLX and EGL calling convention. We go
ahead and define __DRI_CTX_FLAG_RESET_ISOLATION
as well, and update the
drivers to refuse it since we don't support it yet.
This means mismatched drivers/loaders will not be able to create no-error contexts. Too bad. If you want performance that badly you can build both things at once.