Phase 2.1: Implement btrfs support

- Create lib/btrfs.sh with full btrfs installation functions
- Subvolume layout matching ZFS datasets (10 subvols)
- Snapper configuration with timeline policy
- GRUB + grub-btrfs for snapshot boot menu
- Update disk.sh for filesystem-aware partition type
- Update archangel with install_btrfs() path
- Update build.sh to include lib/btrfs.sh
- Update plan with Phase 2.7 (test) and 2.8 (LUKS)

2 files changed, 432 insertions, 2 deletions

diff --git a/custom/lib/btrfs.sh b/custom/lib/btrfs.sh
new file mode 100644
index 0000000..c264fce
--- /dev/null
+++ b/custom/lib/btrfs.sh
@@ -0,0 +1,423 @@
+#!/usr/bin/env bash
+# btrfs.sh - Btrfs-specific functions for archangel installer
+# Source this file after common.sh, config.sh, disk.sh
+
+#############################
+# Btrfs Constants
+#############################
+
+# Mount options for btrfs subvolumes
+BTRFS_OPTS="noatime,compress=zstd,space_cache=v2,discard=async"
+
+# Subvolume layout (matches ZFS dataset structure)
+# Format: "name:mountpoint:extra_opts"
+BTRFS_SUBVOLS=(
+    "@:/::"
+    "@home:/home::"
+    "@snapshots:/.snapshots::"
+    "@var_log:/var/log::"
+    "@var_cache:/var/cache::"
+    "@tmp:/tmp::nosuid,nodev"
+    "@var_tmp:/var/tmp::nosuid,nodev"
+    "@media:/media::compress=no"
+    "@vms:/vms::nodatacow,compress=no"
+    "@var_lib_docker:/var/lib/docker::"
+)
+
+#############################
+# Btrfs Pre-flight
+#############################
+
+btrfs_preflight() {
+    step "Checking Btrfs Requirements"
+
+    # Check for btrfs-progs
+    if ! command_exists mkfs.btrfs; then
+        error "btrfs-progs not installed. Cannot create btrfs filesystem."
+    fi
+    info "btrfs-progs available."
+
+    # Check for required tools
+    require_command btrfs
+    require_command grub-install
+
+    info "Btrfs preflight checks passed."
+}
+
+#############################
+# Btrfs Volume Creation
+#############################
+
+create_btrfs_volume() {
+    local partition="$1"
+
+    step "Creating Btrfs Filesystem"
+
+    info "Formatting $partition as btrfs..."
+    mkfs.btrfs -f -L "archroot" "$partition" || error "Failed to create btrfs filesystem"
+
+    info "Btrfs filesystem created on $partition"
+}
+
+#############################
+# Subvolume Creation
+#############################
+
+create_btrfs_subvolumes() {
+    local partition="$1"
+
+    step "Creating Btrfs Subvolumes"
+
+    # Mount the raw btrfs volume temporarily
+    mount "$partition" /mnt || error "Failed to mount btrfs volume"
+
+    # Create each subvolume
+    for subvol_spec in "${BTRFS_SUBVOLS[@]}"; do
+        IFS=':' read -r name mountpoint extra <<< "$subvol_spec"
+        info "Creating subvolume: $name -> $mountpoint"
+        btrfs subvolume create "/mnt/$name" || error "Failed to create subvolume $name"
+    done
+
+    # Unmount raw volume
+    umount /mnt
+
+    info "Created ${#BTRFS_SUBVOLS[@]} subvolumes."
+}
+
+#############################
+# Btrfs Mount Functions
+#############################
+
+mount_btrfs_subvolumes() {
+    local partition="$1"
+
+    step "Mounting Btrfs Subvolumes"
+
+    # Mount root subvolume first
+    info "Mounting @ -> /mnt"
+    mount -o "subvol=@,$BTRFS_OPTS" "$partition" /mnt || error "Failed to mount root subvolume"
+
+    # Create mount points and mount remaining subvolumes
+    for subvol_spec in "${BTRFS_SUBVOLS[@]}"; do
+        IFS=':' read -r name mountpoint extra <<< "$subvol_spec"
+
+        # Skip root, already mounted
+        [[ "$name" == "@" ]] && continue
+
+        # Build mount options
+        local opts="subvol=$name,$BTRFS_OPTS"
+
+        # Apply extra options (override defaults where specified)
+        if [[ -n "$extra" ]]; then
+            # Handle compress=no by removing compress from opts and not adding it
+            if [[ "$extra" == *"compress=no"* ]]; then
+                opts=$(echo "$opts" | sed 's/,compress=zstd//')
+            fi
+            # Handle nodatacow
+            if [[ "$extra" == *"nodatacow"* ]]; then
+                opts="$opts,nodatacow"
+                opts=$(echo "$opts" | sed 's/,compress=zstd//')
+            fi
+            # Handle nosuid,nodev for tmp
+            if [[ "$extra" == *"nosuid"* ]]; then
+                opts="$opts,nosuid,nodev"
+            fi
+        fi
+
+        info "Mounting $name -> /mnt$mountpoint"
+        mkdir -p "/mnt$mountpoint"
+        mount -o "$opts" "$partition" "/mnt$mountpoint" || error "Failed to mount $name"
+    done
+
+    # Set permissions on tmp directories
+    chmod 1777 /mnt/tmp /mnt/var/tmp
+
+    info "All subvolumes mounted."
+}
+
+#############################
+# Fstab Generation
+#############################
+
+generate_btrfs_fstab() {
+    local partition="$1"
+    local efi_partition="$2"
+
+    step "Generating fstab"
+
+    local uuid
+    uuid=$(blkid -s UUID -o value "$partition")
+
+    # Start with header
+    cat > /mnt/etc/fstab << EOF
+# /etc/fstab - Btrfs subvolume mounts
+# IMPORTANT: Using subvol= NOT subvolid= for snapshot compatibility
+# Generated by archangel installer
+
+EOF
+
+    # Add each subvolume
+    for subvol_spec in "${BTRFS_SUBVOLS[@]}"; do
+        IFS=':' read -r name mountpoint extra <<< "$subvol_spec"
+
+        # Build mount options
+        local opts="subvol=$name,$BTRFS_OPTS"
+
+        # Apply extra options
+        if [[ -n "$extra" ]]; then
+            if [[ "$extra" == *"compress=no"* ]]; then
+                opts=$(echo "$opts" | sed 's/,compress=zstd//')
+            fi
+            if [[ "$extra" == *"nodatacow"* ]]; then
+                opts="$opts,nodatacow"
+                opts=$(echo "$opts" | sed 's/,compress=zstd//')
+            fi
+            if [[ "$extra" == *"nosuid"* ]]; then
+                opts="$opts,nosuid,nodev"
+            fi
+        fi
+
+        echo "UUID=$uuid  $mountpoint  btrfs  $opts  0 0" >> /mnt/etc/fstab
+    done
+
+    # Add EFI partition
+    local efi_uuid
+    efi_uuid=$(blkid -s UUID -o value "$efi_partition")
+    echo "" >> /mnt/etc/fstab
+    echo "# EFI System Partition" >> /mnt/etc/fstab
+    echo "UUID=$efi_uuid  /efi  vfat  defaults,noatime  0 2" >> /mnt/etc/fstab
+
+    info "fstab generated with ${#BTRFS_SUBVOLS[@]} btrfs mounts + EFI"
+}
+
+#############################
+# Snapper Configuration
+#############################
+
+configure_snapper() {
+    step "Configuring Snapper"
+
+    # Snapper config for root
+    # Note: snapper expects /.snapshots to exist and be a subvolume
+    info "Creating snapper config for root..."
+
+    arch-chroot /mnt snapper -c root create-config / || error "Failed to create snapper config"
+
+    # Snapper creates its own .snapshots subvolume, but we already have @snapshots
+    # Delete snapper's and use ours
+    arch-chroot /mnt btrfs subvolume delete /.snapshots 2>/dev/null || true
+    mkdir -p /mnt/.snapshots
+
+    # Set snapper timeline settings
+    # Keep: 6 hourly, 7 daily, 2 weekly, 1 monthly
+    info "Configuring snapshot retention policy..."
+    cat > /mnt/etc/snapper/configs/root << 'EOF'
+# Snapper config for root filesystem
+SUBVOLUME="/"
+FSTYPE="btrfs"
+QGROUP=""
+
+# Automatic timeline snapshots
+TIMELINE_CREATE="yes"
+TIMELINE_CLEANUP="yes"
+
+# Retention policy
+TIMELINE_MIN_AGE="1800"
+TIMELINE_LIMIT_HOURLY="6"
+TIMELINE_LIMIT_DAILY="7"
+TIMELINE_LIMIT_WEEKLY="2"
+TIMELINE_LIMIT_MONTHLY="1"
+TIMELINE_LIMIT_YEARLY="0"
+
+# Cleanup settings
+NUMBER_CLEANUP="yes"
+NUMBER_MIN_AGE="1800"
+NUMBER_LIMIT="50"
+NUMBER_LIMIT_IMPORTANT="10"
+
+# User access
+ALLOW_USERS=""
+ALLOW_GROUPS=""
+
+# Sync ACL
+SYNC_ACL="no"
+
+# Background comparison
+BACKGROUND_COMPARISON="yes"
+
+# Empty pre-post cleanup
+EMPTY_PRE_POST_CLEANUP="yes"
+EMPTY_PRE_POST_MIN_AGE="1800"
+EOF
+
+    # Enable snapper timers
+    arch-chroot /mnt systemctl enable snapper-timeline.timer
+    arch-chroot /mnt systemctl enable snapper-cleanup.timer
+
+    info "Snapper configured with timeline snapshots enabled."
+}
+
+#############################
+# GRUB Configuration
+#############################
+
+configure_grub() {
+    local efi_partition="$1"
+
+    step "Configuring GRUB Bootloader"
+
+    # Mount EFI partition
+    mkdir -p /mnt/efi
+    mount "$efi_partition" /mnt/efi
+
+    # Configure GRUB defaults
+    info "Setting GRUB configuration..."
+    cat > /mnt/etc/default/grub << 'EOF'
+# GRUB configuration for btrfs root with snapshots
+GRUB_DEFAULT=0
+GRUB_TIMEOUT=5
+GRUB_DISTRIBUTOR="Arch"
+GRUB_CMDLINE_LINUX_DEFAULT="loglevel=3 quiet"
+GRUB_CMDLINE_LINUX=""
+
+# Btrfs snapshot boot support
+GRUB_BTRFS_GRUB_DIRNAME="/efi/grub"
+
+# Disable os-prober (single-boot system)
+GRUB_DISABLE_OS_PROBER=true
+EOF
+
+    # Install GRUB to EFI
+    info "Installing GRUB to EFI partition..."
+    arch-chroot /mnt grub-install --target=x86_64-efi --efi-directory=/efi --bootloader-id=GRUB \
+        || error "GRUB installation failed"
+
+    # Generate GRUB config
+    info "Generating GRUB configuration..."
+    arch-chroot /mnt grub-mkconfig -o /boot/grub/grub.cfg \
+        || error "Failed to generate GRUB config"
+
+    # Enable grub-btrfsd for automatic snapshot menu updates
+    info "Enabling grub-btrfs daemon..."
+    arch-chroot /mnt systemctl enable grub-btrfsd
+
+    info "GRUB configured with btrfs snapshot support."
+}
+
+#############################
+# Pacman Snapshot Hook
+#############################
+
+configure_btrfs_pacman_hook() {
+    step "Configuring Pacman Snapshot Hook"
+
+    # snap-pac handles this automatically when installed
+    # Just verify it's set up
+    info "snap-pac will create pre/post snapshots for pacman transactions."
+    info "Snapshots visible in GRUB menu via grub-btrfs."
+}
+
+#############################
+# Genesis Snapshot
+#############################
+
+create_btrfs_genesis_snapshot() {
+    step "Creating Genesis Snapshot"
+
+    # Use snapper to create the genesis snapshot
+    arch-chroot /mnt snapper -c root create --description "genesis" \
+        || error "Failed to create genesis snapshot"
+
+    info "Genesis snapshot created."
+    info "Restore with: snapper -c root rollback <number>"
+
+    # Show the snapshot
+    arch-chroot /mnt snapper -c root list
+}
+
+#############################
+# Btrfs Services
+#############################
+
+configure_btrfs_services() {
+    step "Configuring System Services"
+
+    # Enable standard services
+    arch-chroot /mnt systemctl enable NetworkManager
+    arch-chroot /mnt systemctl enable avahi-daemon
+
+    # Snapper timers (already enabled in configure_snapper)
+
+    # grub-btrfsd (already enabled in configure_grub)
+
+    info "System services configured."
+}
+
+#############################
+# Btrfs Initramfs
+#############################
+
+configure_btrfs_initramfs() {
+    step "Configuring Initramfs for Btrfs"
+
+    # Backup original
+    cp /mnt/etc/mkinitcpio.conf /mnt/etc/mkinitcpio.conf.bak
+
+    # Remove archiso drop-in if present
+    if [[ -f /mnt/etc/mkinitcpio.conf.d/archiso.conf ]]; then
+        info "Removing archiso drop-in config..."
+        rm -f /mnt/etc/mkinitcpio.conf.d/archiso.conf
+    fi
+
+    # Create proper linux-lts preset
+    info "Creating linux-lts preset..."
+    cat > /mnt/etc/mkinitcpio.d/linux-lts.preset << 'EOF'
+# mkinitcpio preset file for linux-lts
+
+PRESETS=(default fallback)
+
+ALL_kver="/boot/vmlinuz-linux-lts"
+
+default_image="/boot/initramfs-linux-lts.img"
+
+fallback_image="/boot/initramfs-linux-lts-fallback.img"
+fallback_options="-S autodetect"
+EOF
+
+    # Configure hooks for btrfs
+    # btrfs module is built into kernel, but we need the btrfs hook for multi-device
+    sed -i 's/^HOOKS=.*/HOOKS=(base udev microcode modconf kms keyboard keymap consolefont block filesystems fsck)/' \
+        /mnt/etc/mkinitcpio.conf
+
+    # Regenerate initramfs
+    info "Regenerating initramfs..."
+    arch-chroot /mnt mkinitcpio -P
+
+    info "Initramfs configured for btrfs."
+}
+
+#############################
+# Btrfs Cleanup
+#############################
+
+btrfs_cleanup() {
+    step "Cleaning Up Btrfs"
+
+    # Unmount in reverse order
+    info "Unmounting subvolumes..."
+
+    # Unmount EFI first
+    umount /mnt/efi 2>/dev/null || true
+
+    # Unmount all btrfs subvolumes (reverse order)
+    for ((i=${#BTRFS_SUBVOLS[@]}-1; i>=0; i--)); do
+        IFS=':' read -r name mountpoint extra <<< "${BTRFS_SUBVOLS[$i]}"
+        [[ "$name" == "@" ]] && continue
+        umount "/mnt$mountpoint" 2>/dev/null || true
+    done
+
+    # Unmount root last
+    umount /mnt 2>/dev/null || true
+
+    info "Btrfs cleanup complete."
+}
diff --git a/custom/lib/disk.sh b/custom/lib/disk.sh
index fa3dbd2..38c6dd9 100644
--- a/custom/lib/disk.sh
+++ b/custom/lib/disk.sh
@@ -8,10 +8,17 @@
 
 # Partition a single disk for ZFS/Btrfs installation
 # Creates: EFI partition (512M) + root partition (rest)
+# Uses global FILESYSTEM variable to determine partition type
 partition_disk() {
     local disk="$1"
     local efi_size="${2:-512M}"
 
+    # Determine root partition type based on filesystem
+    local root_type="BF00"  # ZFS (Solaris root)
+    if [[ "$FILESYSTEM" == "btrfs" ]]; then
+        root_type="8300"    # Linux filesystem
+    fi
+
     info "Partitioning $disk..."
 
     # Wipe existing partition table
@@ -20,8 +27,8 @@ partition_disk() {
     # Create EFI partition (512M, type EF00)
     sgdisk -n 1:0:+${efi_size} -t 1:EF00 -c 1:"EFI" "$disk" || error "Failed to create EFI partition on $disk"
 
-    # Create root partition (rest of disk, type BF00 for ZFS or 8300 for Linux)
-    sgdisk -n 2:0:0 -t 2:BF00 -c 2:"ROOT" "$disk" || error "Failed to create root partition on $disk"
+    # Create root partition (rest of disk)
+    sgdisk -n 2:0:0 -t 2:$root_type -c 2:"ROOT" "$disk" || error "Failed to create root partition on $disk"
 
     # Notify kernel of partition changes
     partprobe "$disk" 2>/dev/null || true