v0.5.5: crash reports go to a dedicated CRASHLOG USB stick

The fault handler now writes crash.log to the volume labeled CRASHLOG
(label-selected via fat::crash_vol), falling back to slot 0.  On real
hardware the boot USB may be unwritable, so a second stick labeled
CRASHLOG survives the write; the shell auto-prints the previous crash
report from it at next boot (read_crash_log resolves /disk/<uid>/crash.log
through the FAT path, since Disk nodes hold no cached children).

- fat.rs: volume_label() + crash_vol() (no allocation)
- fs.rs: write_crash_log targets crash_vol(); read_crash_log prefers the
  CRASHLOG disk node; drop now-unused first_disk()
- mkdisk.sh: --label option
- test-fault.sh: boots with a dedicated CRASHLOG stick (mkfs -F 32 -n
  CRASHLOG), verifies crash.log lands there and NOT on the ESP

1 files changed, 8 insertions, 2 deletions

diff --git a/scripts/mkdisk.sh b/scripts/mkdisk.sh
index 6bdd50c..2c62f76 100755
--- a/scripts/mkdisk.sh
+++ b/scripts/mkdisk.sh
@@ -9,6 +9,7 @@
 #   ./scripts/mkdisk.sh --size 128M     # different size (default 64M)
 #   ./scripts/mkdisk.sh /path/img       # custom image path
 #   ./scripts/mkdisk.sh --no-seed       # skip the seed/ directory
+#   ./scripts/mkdisk.sh --label CRASHLOG # volume label (default RSDOS)
 #
 # The image is created with `mkfs.fat -C`, which is the option that
 # actually creates the file — plain `mkfs.fat` only writes into an
@@ -23,6 +24,7 @@ IMG="/tmp/disk.img"
 SIZE="64M"
 FRESH=0
 SEED_DIR="$PROJECT_DIR/seed"
+LABEL="RSDOS"
 
 while [ $# -gt 0 ]; do
         case "$1" in
@@ -32,6 +34,10 @@ while [ $# -gt 0 ]; do
                 SIZE="$1"
                 ;;
         --no-seed) SEED_DIR="" ;;
+        --label)
+                shift
+                LABEL="$1"
+                ;;
         --help | -h)
                 head -20 "$0" | grep "^#" | sed 's/^# \?//'
                 exit 0
@@ -65,9 +71,9 @@ if [ -z "$SIZE_BLOCKS" ] || [ "$SIZE_BLOCKS" -le 0 ] 2>/dev/null; then
         exit 1
 fi
 
-echo "mkdisk: creating $IMG ($SIZE FAT32, label RSDOS)"
+echo "mkdisk: creating $IMG ($SIZE FAT32, label $LABEL)"
 rm -f "$IMG"
-mkfs.fat -C -F 32 -n RSDOS "$IMG" "$SIZE_BLOCKS"
+mkfs.fat -C -F 32 -n "$LABEL" "$IMG" "$SIZE_BLOCKS"
 
 if [ -n "$SEED_DIR" ] && [ -d "$SEED_DIR" ]; then
         if ! command -v mcopy >/dev/null 2>&1; then