bug-759139-diagnosis-notes.txt

bug-759139-diagnosis-notes.txt (text/plain), 2.94 KB, created by kfm on 2020-12-12 02:06:20 UTC

In my case, with_dri is true because:

	with_dri = dri_drivers.length() != 0

In turn, the reason is that the ebuild specifies -Ddri-drivers=swrast.

However, it can also be set to true in this way:

	if with_gallium and system_has_kms_drm
	  _glx = get_option('glx')
	  _egl = get_option('egl')
	  if _glx == 'dri' or _egl == 'enabled' or (_glx == 'disabled' and _egl != 'disabled')
	    with_dri = true
	  endif
	endif

Breaking it down:

with_gallium       = true if -Dgallium-drivers is non-empty
	* for that to happen, the ebuild must have called gallium_enable()
	* and for that to happen, USE="gallium" must have been set; hence isolatable
system_has_kms_drm = always true for linux
_glx               = "dri" if USE="X" (otherwise "disabled")
_egl               = "enabled" if USE="egl" (otherwise "disabled")

Later, the check that raises the error happens:

	if with_dri
	  if with_glx == 'disabled'
			and not with_egl
			and not with_gbm
			and with_osmesa != 'classic'
	    error('building dri drivers require at least one windowing system or classic osmesa')
	  endif
	endif

with_glx    = "disabled" because the ebuild specified -Dglx=disabled
	* in turn, that is because of USE="-X"
with_gbm    = "disabled" because the ebuild specified -Dgbm=disabled
	* in turn, that is because of USE="-gbm"
with_osmesa = "none" because the ebuild specified -Dosmesa=none
	* in turn, that is because of USE="-gallium -classic"
	* In other words, USE="classic" would work around the problem
	* However, USE="classic" doesn't affect -Dosmesa unless USE="osmesa" also

It looks as though DRI_DRIVERS is never empty in the ebuild. One potential solution (probably incomplete) is:

	|| ( X classic egl gbm osmesa )
	classic? ( || ( X         egl gbm osmesa ) )
	osmesa?  ( || ( X classic egl gbm        ) )

Alternatively:

	|| ( X classic egl gbm osmesa )
	classic? ( !osmesa?  ( || ( X egl gbm ) ) )
	osmesa?  ( !classic? ( || ( X egl gbm ) ) )

There is another snag, which is that, if neither USE="X" nor USE="wayland" is in effect, the ebuild doesn't pass -Dplatforms at all. In that case, the build system infers that both x11 and wayland should be targetted, leading to this error:

	Build-time dependency wayland-scanner found: NO (tried pkgconfig and cmake)

That much is easy to solve. Simply have the ebuild append -Dplatforms to emesonargs, unconditionally. For it not to specify a platform at all is tolerated by the build system. Alas, doing so reveals another QA issue. Testing with USE="classic osmesa", the build actually concludes successfully, which is good. However, mesa then produces some files that can also be provided by libglvnd, leading to a conflict. Specifically:

	/usr/include/GL/gl.h
	/usr/include/GL/glcorearb.h
	/usr/include/GL/glext.h
	/usr/include/KHR/khrplatform.h

Once the appropriate solution/constraint is applied in view if this problem, an overall solution may be close at hand. Also, I should take a closer look at how USE="gallium" may need to factor into it, if at all.