Rename Schunix to SchOS; the kernel becomes SchIFT

Removes the "-unix" element and with it any trademark exposure to The
Open Group.

The split follows the ecosystem layout: SchOS is the system, and the
kernel has its own name. Kernel-identity strings are the only places
that take SchIFT -- uname(2) sysname, /proc/version, and the two licence
sentences that say "kernel" outright. That is what every Unix does here:
`uname -s` on Linux reports the kernel, not the distribution. Everything
a user reads as the product -- panic screen, boot menu, error prefixes,
docs, LICENSE, NOTICE -- is SchOS.

schunix.img is schos.img, the logo assets and the musl TLS patch are
renamed, and __SCHUNIX__ is __SCHOS__ (the define and the patch that
consumes it moved together).

Two things the rename broke, both found by the bootcheck suite:

  - shmtest wrote "SCHUNIX-MMAP-OK" with a hardcoded length of 15 and
    compared it back by hand-counted offsets (m[3]=='U', m[14]=='K').
    The shorter marker left the write running two bytes past the literal
    and the compare reading past the data, failing a file-backed mmap
    that was working correctly. Now written and compared through one
    constant with sizeof.
  - bootcheck asserted a 31-byte file after appending to
    "hello-from-schunix"; the shorter string makes it 29.

Both are the same mistake: a string literal whose length is written out
somewhere else. Full suite green -- base, Tty, Ps, Sock, Fb, Usb, Evdev.

include/errno.h

@@ -1,8 +1,8 @@
 // Error numbers, matching the Linux x86_64 ABI values so that musl-linked
 // programs interpret syscall failures correctly. Kernel code returns these
 // negated (e.g. `return -ENOSYS;`), exactly like Linux does internally.
-#ifndef SCHUNIX_ERRNO_H
-#define SCHUNIX_ERRNO_H
+#ifndef SCHOS_ERRNO_H
+#define SCHOS_ERRNO_H
 
 #define EPERM        1   // Operation not permitted
 #define ENOENT       2   // No such file or directory
@@ -57,4 +57,4 @@
 #define ENOTCONN       107   // Transport endpoint is not connected
 #define ECONNREFUSED   111   // Connection refused
 
-#endif // SCHUNIX_ERRNO_H
+#endif // SCHOS_ERRNO_H

include/fb.h

@@ -3,7 +3,7 @@
 // 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
+// SchOS 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
@@ -76,7 +76,7 @@ struct fb_var_screeninfo {
 };
 
 struct fb_fix_screeninfo {
-    char id[16];                   // "schunixfb"
+    char id[16];                   // "schosfb"
     unsigned long smem_start;      // physical address of the framebuffer
     unsigned int smem_len;         // its length in bytes
     unsigned int type;

include/fcntl.h

@@ -6,7 +6,7 @@
 // the userland is built against a libc that sends Linux flag values, and the
 // kernel reads them with these constants. They disagreed for a long time, with
 // results that looked like filesystem corruption rather than like a mistake --
-// Linux O_APPEND (0x400) landed on Schunix's O_TRUNC, so `cmd >> file`
+// Linux O_APPEND (0x400) landed on SchOS's O_TRUNC, so `cmd >> file`
 // truncated the file it was meant to extend, and Linux O_TRUNC (0x200) landed
 // on O_CREATE, so `cmd > file` left whatever was past the new end in place.
 // Neither failure pointed anywhere near a header.
@@ -29,7 +29,7 @@
 #define O_NOFOLLOW  0x020000   /* Linux O_NOFOLLOW  (0400000)  */
 #define O_CLOEXEC   0x080000   /* Linux O_CLOEXEC   (02000000) */
 
-// Schunix-only, placed above every flag Linux defines so it can never be
+// SchOS-only, placed above every flag Linux defines so it can never be
 // mistaken for one. 0x40000 was used before and collides with Linux O_NOATIME.
 #define O_EXTENT    0x8000000  /* sparse-extent hint */
 

include/font.h

@@ -1,4 +1,4 @@
-/* Schunix OS System Font - 8x16, 256 glyphs.
+/* SchOS OS System Font - 8x16, 256 glyphs.
  *
  * The upper half is CP437, the IBM PC character set: 0x82 is 'e' with an
  * acute, 0xE9 is a capital theta, 0xB0-0xDF are shading and box-drawing.

include/input.h

@@ -81,7 +81,7 @@ struct input_event {
 // EVIOCGRAB -- take/release exclusive access to a device.
 //
 // Linux's _IOW('E', 0x90, int). Spelled as the resulting constant rather than
-// built from an _IOW macro because Schunix has no ioctl-encoding macros and
+// built from an _IOW macro because SchOS has no ioctl-encoding macros and
 // inventing a set just for this would be a bigger change than the feature.
 // A non-zero argument grabs, zero releases; the argument is passed by value.
 #define EVIOCGRAB       0x40044590

include/logo.h

@@ -1,7 +1,7 @@
 #pragma once
 
 // GENERATED by tools/mklogo.py -- do not edit. Run `make logo`.
-//   source: Assets/Schunix Small Logo.png
+//   source: Assets/SchOS Small Logo.png
 //
 // An ink-coverage mask, not colour: 0 is background and full scale is
 // solid logo. Whoever draws it picks the colour, so the palette stays in

include/pci.h

@@ -2,7 +2,7 @@
 
 // PCI bus enumeration and driver binding.
 //
-// Until this existed, every driver in Schunix found its hardware by knowing
+// Until this existed, every driver in SchOS found its hardware by knowing
 // where it was: IDE at 0x1F0 because IDE has always been at 0x1F0, the
 // framebuffer wherever the BIOS's VBE call said. That works for exactly the
 // devices that predate PCI and for nothing else. A NIC, an AHCI controller,

include/posix.h

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: Apache-2.0
-// Schunix — POSIX-compatibility types used by kernel syscall handlers.
+// SchOS — POSIX-compatibility types used by kernel syscall handlers.
 #pragma once
 #include "types.h"
 #include "date.h"

include/theme.h

@@ -1,6 +1,6 @@
 #pragma once
 
-// Schunix visual identity — one palette, shared by everything that draws.
+// SchOS visual identity — one palette, shared by everything that draws.
 //
 // This header exists because there were three unrelated designs and the seams
 // showed. The bootloader splash was deep purple with gold text, deliberately

include/uaccess.h

@@ -11,13 +11,13 @@
 //      unrelated physical page at the next 4K boundary. Any multi-byte
 //      access through it must stay within a single page.
 //
-// These helpers encapsulate both rules. Because Schunix (like old x86
+// These helpers encapsulate both rules. Because SchOS (like old x86
 // without SMAP) keeps the user page table active in kernel mode, a raw
 // user virtual address is directly dereferenceable once the whole range
 // has been validated — that is what user_ptr() hands back, and why the
 // result is safe across page boundaries where a uva2ka() pointer is not.
-#ifndef SCHUNIX_UACCESS_H
-#define SCHUNIX_UACCESS_H
+#ifndef SCHOS_UACCESS_H
+#define SCHOS_UACCESS_H
 
 #include "types.h"
 
@@ -46,4 +46,4 @@ int copy_to_user(addr_t uaddr, const void *src, uint64 n);
 // or exceeds USER_STR_MAX.
 long strlen_user(addr_t uaddr);
 
-#endif // SCHUNIX_UACCESS_H
+#endif // SCHOS_UACCESS_H