gallium-xlib: query MIT-SHM before using it.
When Mesa is compiled for gallium-xlib using e.g. ./configure --enable-glx=gallium-xlib --disable-dri --disable-gbm -disable-egl and is used by an X server (usually remotely via SSH X11 forwarding) that does not support MIT-SHM such as XMing or MobaXterm, OpenGL clients report error messages such as Xlib: extension "MIT-SHM" missing on display "localhost:11.0". ad infinitum.
The reason is that the code in src/gallium/winsys/sw/xlib uses MIT-SHM without checking for its existence, unlike the code in src/glx/drisw_glx.c and src/mesa/drivers/x11/xm_api.c. I copied the same check using XQueryExtension, and tested with glxgears on MobaXterm.
This issue was reported before here: https://lists.freedesktop.org/archives/mesa-users/2016-July/001183.html Reviewed-by: Eric Anholt email@example.com Reviewed-by: Emil Velikov firstname.lastname@example.org Cc: email@example.com