add multi-sink diagnostic log; make framebuffer optional

src/root.zig

@@ -24,12 +24,21 @@ pub const PixelFormat = enum(u32) {
 /// A linear framebuffer: `width`x`height` pixels, each a 32-bit value, with
 /// `pitch` bytes between the start of one row and the next (which may be larger
 /// than `width * 4` due to hardware padding).
+///
+/// A `base` of 0 means **no framebuffer** — the firmware exposed no Graphics
+/// Output Protocol (a headless server, say). The kernel must treat on-screen
+/// output as optional and never assume a framebuffer exists.
 pub const Framebuffer = extern struct {
-    base: usize,            // the memory address where pixel data starts
+    base: usize,            // the memory address where pixel data starts (0 = none)
     width: u32,             // visible pixels per row (e.g. 1920)
     height: u32,            // visible rows (e.g. 1080)
     pitch: u32,             // bytes from the start of one row to the start of the next
     format: PixelFormat,
+
+    /// Whether a usable framebuffer was handed over.
+    pub fn present(self: Framebuffer) bool {
+        return self.base != 0 and self.width != 0 and self.height != 0;
+    }
 };
 
 /// Page size the memory map is measured in. 4 KiB on every architecture danos