Faster ISO builds (69 s to 9 s) and a faster write.sh check

make iso recompiled the kernel and every command each time: iso and
ramroot wiped build/kernel, build/lib and build/cmd to make sure nothing
was compiled for the wrong RAMROOT setting. Only kernel/proc/proc.c and
kernel/dev/ramdisk.c read RAMDISK_ROOT, so only their objects go now.

Even then a no-op make iso took 69 s, because sysroot.stamp lists every
staged file with its mtime and two things re-copied files on every run:
the plain cp in etc-install (now cp -p) and fastfetch's install (now
install -C). A changed stamp rebuilds the Alpine root, the root image
and its zstd -19 compression. A no-op, and a one-file kernel change,
now take about 9 s.

write.sh read the stick back with a buffered cmp, slowly and possibly from
the page cache. It now reads 4 MB at a time with iflag=direct, which
checks the stick itself; --no-verify skips the check.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015f73FesGZGYPkmDvUcj6QX

Makefile

@@ -528,11 +528,18 @@ endif
 #
 # Evaluated when the Makefile is read, so the wipe happens before anything is
 # compiled against the wrong setting.
+#
+# Only the two objects that read RAMDISK_ROOT are dropped: kernel/proc/proc.c
+# (ROOTDEV is used nowhere else) and kernel/dev/ramdisk.c. The whole of
+# build/kernel, build/lib and build/cmd used to go, which made every `make iso`
+# recompile the kernel and every command, rebuild the root image from the new
+# binaries and compress it again at zstd -19 -- minutes, for a one-line change.
+# If another file ever starts to use ROOTDEV or RAMDISK_ROOT, add it here.
 RAMROOT_STATE := $(if $(RAMROOT),on,off)
 RAMROOT_STAMP := $(BUILD)/ramroot.state
 $(shell mkdir -p $(BUILD); \
         if [ "$$(cat $(RAMROOT_STAMP) 2>/dev/null)" != "$(RAMROOT_STATE)" ]; then \
-            rm -rf $(BUILD)/kernel $(BUILD)/lib $(BUILD)/cmd; \
+            rm -f $(BUILD)/kernel/proc/proc.o $(BUILD)/kernel/dev/ramdisk.o; \
             printf '%s' '$(RAMROOT_STATE)' > $(RAMROOT_STAMP); \
         fi)
 
@@ -738,7 +745,6 @@ qemu-uefi: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
 # silently reused for the other, leaving ROOTDEV pointing at the wrong device.
 # Dropping the compiled objects first makes the switch always correct.
 ramroot:
-	rm -rf $(BUILD)/kernel $(BUILD)/lib $(BUILD)/cmd
 	$(MAKE) RAMROOT=1
 
 cmd: $(CMDBINS)
@@ -781,7 +787,6 @@ projects:
 # CFLAGS and make cannot see that.
 # -----------------------------------------------------------------------
 iso:
-	rm -rf $(BUILD)/kernel $(BUILD)/lib $(BUILD)/cmd
 	$(MAKE) RAMROOT=1 schos.iso
 
 # One El Torito entry, pointing at a FAT image holding the loader and kernel.
@@ -1458,19 +1463,23 @@ LOGO_ASCII = docs/branding/Ascii/ascii_50.txt
 # proves the same thing far less clearly.
 SRV_FILES = $(wildcard srv/*)
 
+# cp -p, not cp: sysroot.stamp lists every staged file with its mtime, and the
+# Alpine root, the root image and its zstd -19 compression are all rebuilt when
+# it changes. A plain cp gave every copy a new mtime, so every `make iso`
+# rebuilt all of them -- over a minute of CPU for no change at all.
 etc-install: $(SCHINIT_JOBS) $(ETC_PLAIN) $(ETC_ZSH) $(LOGO_ASCII) $(SRV_FILES)
 	@mkdir -p $(SYSROOT)/etc/schinit $(SYSROOT)/etc/zsh $(SYSROOT)/usr/share/schos $(SYSROOT)/srv
-	@cp $(ETC_PLAIN) $(SYSROOT)/etc/
+	@cp -p $(ETC_PLAIN) $(SYSROOT)/etc/
-	@cp $(SCHINIT_JOBS) $(SYSROOT)/etc/schinit/
+	@cp -p $(SCHINIT_JOBS) $(SYSROOT)/etc/schinit/
-	@cp $(ETC_ZSH) $(SYSROOT)/etc/zsh/
+	@cp -p $(ETC_ZSH) $(SYSROOT)/etc/zsh/
-	@cp $(LOGO_ASCII) $(SYSROOT)/usr/share/schos/logo.txt
+	@cp -p $(LOGO_ASCII) $(SYSROOT)/usr/share/schos/logo.txt
-	@cp $(SRV_FILES) $(SYSROOT)/srv/
+	@cp -p $(SRV_FILES) $(SYSROOT)/srv/
 	@# The device-name databases, where lspci and lsusb look for them: the
 	@# hwdata package's directory. They were at /usr/share/usb.ids, which no
 	@# tool searches, so lsusb printed numbers only.
 	@mkdir -p $(SYSROOT)/usr/share/hwdata
 	@rm -f $(SYSROOT)/usr/share/usb.ids
-	@for f in usb.ids pci.ids; do [ -f dist/$$f ] && cp dist/$$f $(SYSROOT)/usr/share/hwdata/; done; true
+	@for f in usb.ids pci.ids; do [ -f dist/$$f ] && cp -p dist/$$f $(SYSROOT)/usr/share/hwdata/; done; true
 	@echo "installed $(words $(ETC_PLAIN)) /etc file(s), $(words $(ETC_ZSH)) zsh file(s) and $(words $(SCHINIT_JOBS)) schinit manifest(s)"
 
 # The mount points. Created here rather than by init, because a mkdir on a

ports/fastfetch/Makefile

@@ -91,7 +91,7 @@ $(BUILDDIR)/fastfetch: $(BUILDDIR)/toolchain.cmake
 build: $(BUILDDIR)/fastfetch
 
 install: $(BUILDDIR)/fastfetch | $(SYSROOT)/bin
-	install -m 0755 $(BUILDDIR)/fastfetch $(SYSROOT)/bin/fastfetch
+	install -C -m 0755 $(BUILDDIR)/fastfetch $(SYSROOT)/bin/fastfetch
 
 clean:
 	rm -rf $(PORTDIR)

write.sh

@@ -3,6 +3,7 @@
 #
 #   ./write.sh sdc            or   ./write.sh /dev/sdc
 #   ./write.sh sdc other.iso  to write a different image
+#   ./write.sh sdc --no-verify  skip the read-back check (halves the time)
 #
 # Shows what is on the device, asks you to type the device's name back, then
 # asks for your password and writes. Everything on the device is destroyed;
@@ -26,7 +27,7 @@ fi
 die() { printf '%swrite.sh:%s %s\n' "$R" "$N" "$*" >&2; exit 1; }
 
 usage() {
-    echo "usage: ./write.sh <device> [image.iso] [--any-disk]"
+    echo "usage: ./write.sh <device> [image.iso] [--any-disk] [--no-verify]"
     echo "       ./write.sh sdc        writes schos.iso to /dev/sdc"
     echo
     echo "Removable disks on this machine:"
@@ -36,11 +37,13 @@ usage() {
 }
 
 ANY=0
+VERIFY=1
 DEV=
 ISO=
 for a in "$@"; do
     case "$a" in
         --any-disk) ANY=1 ;;
+        --no-verify) VERIFY=0 ;;
         -h|--help)  usage ;;
         *) if [ -z "$DEV" ]; then DEV=$a; elif [ -z "$ISO" ]; then ISO=$a; else usage; fi ;;
     esac
@@ -127,12 +130,22 @@ sync
 # --- check ------------------------------------------------------------------
 
 # Read it back. A stick that takes the write and keeps none of it is common
-# enough among cheap ones to be worth thirty seconds.
+# enough among cheap ones to be worth the time.
-echo "Checking what was written..."
+#
-if sudo cmp -n "$ISO_BYTES" "$ISO" "$DEV"; then
+# iflag=direct and 4 MB reads: a plain `cmp ISO /dev/sdX` reads through the page
+# cache in small requests, which a USB stick serves slowly -- and may be answered
+# from the cache rather than from the stick, checking nothing. Direct reads
+# check the stick itself, and at the speed it can actually deliver.
+if [ "$VERIFY" = 1 ]; then
+    echo "Checking what was written..."
+    BLOCKS=$(( (ISO_BYTES + 4194303) / 4194304 ))
+    if sudo dd if="$DEV" bs=4M count="$BLOCKS" iflag=direct status=none | cmp -n "$ISO_BYTES" - "$ISO"; then
         echo "${G}Done.${N} $DEV holds $(basename "$ISO") and can be removed."
-else
+    else
         die "the device does not read back what was written -- the stick may be failing"
+    fi
+else
+    echo "${G}Done.${N} $DEV holds $(basename "$ISO") (not verified) and can be removed."
 fi
 
 # The kernel re-reads the partition table so the new layout shows up here