SCFF: the live root ships compressed, with Xorg and Window Maker

SCFF, the SchOS Compressed File Format (include/fs/scff.h), is a block
image cut into 128 KB chunks, each its own zstd frame, behind an index.
tools/mkscff writes it from fs-ram.img on every core (-19, 11 s) and
checks each chunk decompresses to itself. The kernel carries the .scff
as its ramdisk and unpacks a chunk the first time a block in it is
read; zero blocks share one page. The kernel and the ISO are the
compressed size, and the root costs memory only for what is touched.
See docs/architecture/scff.md.

zstd 1.5.7 comes from ports/zstd like uACPI: the decoder is compiled
into the kernel at -O2, with a static context and a 64 KB stack of its
own, and mkscff builds the whole library from the same release.

world now has xorg-server, the fbdev and evdev drivers, xinit, Window
Maker, xterm and DejaVu, and /root/.xinitrc runs wmaker. That root is
358 MB, 102 MB as SCFF.

The ISO no longer carries the root a third time as an ISO 9660 tree,
which nothing read. schos.iso: 1389 MB -> 318 MB. El Torito keeps its
own copy of the EFI image, the layout real machines have booted.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

tools/posix/mkaroot.sh

@@ -109,6 +109,13 @@ cat > "$P/root/.xserverrc" <<'XEOF'
 exec /usr/bin/X -nolisten tcp -dumbSched "$@"
 XEOF
 
+# What startx runs inside it: Window Maker, which world installs. Without this
+# xinit falls back to twm and an xterm, neither of which is in the image.
+cat > "$P/root/.xinitrc" <<'XEOF'
+#!/bin/sh
+exec wmaker
+XEOF
+
 # Mount points and runtime directories are alpine-baselayout's; an empty
 # directory here only duplicates it.
 for d in dev proc sys run tmp srv; do

tools/posix/mkiso.sh

@@ -3,11 +3,16 @@
 #
 #   tools/posix/mkiso.sh [output.iso]
 #
-# The disc carries one El Torito boot entry and a real directory tree:
+# The disc carries one El Torito boot entry and the loader and kernel as files:
 #
 #   /boot/efiboot.img      a FAT image holding the loader and the kernel
 #   /EFI/BOOT/BOOTX64.EFI  the same loader, visible as a file on the disc
-#   /bin /etc /usr ...     the staged sysroot, as an ordinary hierarchy
+#   /schos/kernel          the same kernel, for chainloaders (below)
+#
+# The root filesystem is inside the kernel, as its ramdisk. The disc used to
+# carry it a third time as an ISO 9660 tree, which nothing reads -- SchOS has
+# no ISO 9660 driver -- and once Xorg was in the root that copy alone was
+# 360 MB.
 #
 # --- Why only one entry -----------------------------------------------------
 #
@@ -69,7 +74,6 @@ cd "$repo"
 
 BUILD=${BUILD:-build}
 STAGING="$BUILD/iso"
-SYSROOT=${SYSROOT:-sysroot}
 
 KERNEL="$BUILD/kernel/kernel"
 EFIAPP="$BUILD/uefi/BOOTX64.EFI"
@@ -113,9 +117,6 @@ cp "$KERNEL" "$STAGING/schos/kernel"
 # this FAT image -- not the ISO 9660 tree around it. Without the kernel in here
 # the loader comes up and halts with EFI_NOT_FOUND, which is what it did.
 #
-# The ISO 9660 tree still carries the sysroot for a running system to read; the
-# loader's own two files live in here because that is the volume it is handed.
-#
 # Sized from what actually goes in plus slack, rather than fixed: a hardcoded
 # size is a thing that breaks quietly the first time the kernel grows.
 EFI_IMG="$STAGING/boot/efiboot.img"
@@ -145,15 +146,6 @@ if true; then
     mcopy -i "$EFI_IMG" "$KERNEL" ::/schos/kernel
 fi
 
-# The sysroot, as an ordinary hierarchy. Copied rather than linked so that
-# whatever ends up on the disc is a snapshot, not a view of a tree that may be
-# rebuilt underneath it.
-if [ -d "$SYSROOT" ]; then
-    for d in "$SYSROOT"/*; do
-        [ -e "$d" ] || continue
-        cp -a "$d" "$STAGING/"
-    done
-fi
 
 # xorriso if it is here, mkisofs otherwise. Both accept the El Torito flags
 # below unchanged -- xorriso's -as mkisofs mode exists precisely to be
@@ -173,6 +165,11 @@ if command -v xorriso >/dev/null 2>&1; then
     # of type 0xEF is what every UEFI firmware looks for on a removable
     # disk, MBR rather than GPT because the oldest ones read that best.
     HYBRID="-append_partition 2 0xef $EFI_IMG"
+    # El Torito keeps its own copy of the image in the tree, the layout real
+    # machines have booted. Pointing it into the partition instead
+    # (--interval:appended_partition_2:all::, as Arch does) saves a copy, and
+    # an ASUS laptop stopped listing the stick the day that was tried. With
+    # the root compressed (SCFF) the copy is only the kernel's size.
 elif command -v mkisofs >/dev/null 2>&1; then
     MKISOFS="mkisofs"
     HYBRID=""