Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

include/fb.h

@@ -0,0 +1,95 @@
+#pragma once
+
+// Framebuffer device ABI -- /dev/fb0.
+//
+// These are Linux's fbdev request numbers and structure layouts, not ours.
+// Schunix invented this device, so nothing forced the choice; matching Linux
+// was still the right one. A framebuffer is the first thing a graphics
+// program looks for, and every such program already knows how to ask
+// FBIOGET_VSCREENINFO. Inventing a private struct would have meant patching
+// each one we ever port, and -- worse -- a Linux-ABI binary calling
+// FBIOGET_VSCREENINFO would have gotten a *differently shaped* answer to a
+// request it thought it understood, which is the failure mode that made
+// `>>` truncate back when include/fcntl.h held xv6's open flags instead of
+// Linux's. Same lesson, applied before it bites rather than after.
+//
+// Plain C types throughout (no types.h) so userspace can include this
+// directly. Both sides are LP64.
+
+#define FBIOGET_VSCREENINFO 0x4600
+#define FBIOPUT_VSCREENINFO 0x4601
+#define FBIOGET_FSCREENINFO 0x4602
+#define FBIOBLANK           0x4611
+
+// fb_fix_screeninfo.type
+#define FB_TYPE_PACKED_PIXELS 0
+
+// fb_fix_screeninfo.visual
+#define FB_VISUAL_TRUECOLOR 2
+
+// fb_var_screeninfo.activate
+#define FB_ACTIVATE_NOW 0
+
+// One colour channel's position within a pixel. `offset` is the bit position
+// of the channel's least significant bit; `length` is how many bits it gets.
+// A length of 0 means the channel does not exist -- which is how an opaque
+// framebuffer reports `transp`.
+struct fb_bitfield {
+    unsigned int offset;
+    unsigned int length;
+    unsigned int msb_right;   // != 0 means bit 0 is the MSB; never here
+};
+
+struct fb_var_screeninfo {
+    unsigned int xres;             // visible resolution
+    unsigned int yres;
+    unsigned int xres_virtual;     // virtual resolution; == visible, no panning
+    unsigned int yres_virtual;
+    unsigned int xoffset;          // offset of visible area within virtual
+    unsigned int yoffset;
+    unsigned int bits_per_pixel;
+    unsigned int grayscale;        // 0 == colour
+    struct fb_bitfield red;
+    struct fb_bitfield green;
+    struct fb_bitfield blue;
+    struct fb_bitfield transp;
+    unsigned int nonstd;           // 0 == standard pixel format
+    unsigned int activate;
+    unsigned int height;           // physical size in mm; 0 == unknown, and
+    unsigned int width;            // VBE does not tell us, so it stays 0
+    unsigned int accel_flags;
+    // Timings. The mode is whatever the bootloader's VBE call established and
+    // we cannot change it, so these are all reported as zero rather than
+    // invented.
+    unsigned int pixclock;
+    unsigned int left_margin;
+    unsigned int right_margin;
+    unsigned int upper_margin;
+    unsigned int lower_margin;
+    unsigned int hsync_len;
+    unsigned int vsync_len;
+    unsigned int sync;
+    unsigned int vmode;
+    unsigned int rotate;
+    unsigned int colorspace;
+    unsigned int reserved[4];
+};
+
+struct fb_fix_screeninfo {
+    char id[16];                   // "schunixfb"
+    unsigned long smem_start;      // physical address of the framebuffer
+    unsigned int smem_len;         // its length in bytes
+    unsigned int type;
+    unsigned int type_aux;
+    unsigned int visual;
+    unsigned short xpanstep;       // 0 == panning unsupported
+    unsigned short ypanstep;
+    unsigned short ywrapstep;
+    unsigned int line_length;      // bytes per scanline (the VBE stride, which
+                                   // is NOT always xres * bytes_per_pixel)
+    unsigned long mmio_start;      // no separate register aperture
+    unsigned int mmio_len;
+    unsigned int accel;            // no acceleration
+    unsigned short capabilities;
+    unsigned short reserved[2];
+};