pc, pc64: set *bootscreen= when framebuffer changes

add bootscreenconf(VGAscr *) function, that is called whenever
the framebuffer configuration is changed by devvga. that way, we
can pass the current setting of the framebuffer to the new
kernel when using /dev/reboot.

sys/src/9/pc/devvga.c

@@ -329,6 +329,7 @@ vgactl(Cmdbuf *cb)
 
 	case CMtextmode:
 		screeninit();
+		bootscreenconf(nil);
 		return;
 
 	case CMsize:
@@ -357,6 +358,7 @@ vgactl(Cmdbuf *cb)
 		deletescreenimage();
 		if(screensize(x, y, z, chan))
 			error(Egreg);
+		bootscreenconf(scr);
 		return;
 
 	case CMactualsize:

sys/src/9/pc/screen.c

@@ -586,7 +586,7 @@ bootmapfb(VGAscr *scr, ulong pa, ulong sz)
 
 /*
  * called early on boot to attach to framebuffer
- * setup by bootloader or firmware.
+ * setup by bootloader/firmware or plan9.
  */
 void
 bootscreeninit(void)
@@ -665,3 +665,23 @@ bootscreeninit(void)
 	scr->cur->enable(scr);
 	cursoron();
 }
+
+/*
+ * called from devvga when the framebuffer is setup
+ * to set *bootscreen= that can be passed on to a
+ * new kernel on reboot.
+ */
+void
+bootscreenconf(VGAscr *scr)
+{
+	char conf[100], chan[30];
+
+	conf[0] = '\0';
+	if(scr != nil && scr->paddr != 0)
+		snprint(conf, sizeof(conf), "%dx%dx%d %s %#p %d\n",
+			scr->gscreen->r.max.x, scr->gscreen->r.max.y,
+			scr->gscreen->depth, chantostr(chan, scr->gscreen->chan),
+			scr->paddr, scr->apsize);
+
+	ksetenv("*bootscreen", conf, 1);
+}

sys/src/9/pc/screen.h

@@ -149,6 +149,9 @@ extern int	screenaperture(int, int);
 extern Rectangle physgscreenr;	/* actual monitor size */
 extern void	blankscreen(int);
 
+extern void	bootscreeninit(void);
+extern void	bootscreenconf(VGAscr*);
+
 extern VGAcur swcursor;
 extern void swcursorinit(void);
 extern void swcursorhide(void);