new util: with-btrfs-seed

1 files changed, 63 insertions, 0 deletions

diff --git a/src/with-btrfs-seed b/src/with-btrfs-seed
new file mode 100755
index 0000000..9f0147e
--- /dev/null
+++ b/src/with-btrfs-seed
@@ -0,0 +1,63 @@
+#!/bin/sh
+
+usage()
+{
+    print >&2 <<EOF
+usage: $0 <file.iso> [command] [args ...]
+
+  default command is bash
+EOF
+    exit $1
+}
+
+error()
+{
+    printf '%s: Error: %s\n' "$0" "$*" >&2
+    exit 1
+}
+
+warning()
+{
+    printf '%s: Warning: %s\n' "$0" "$*" >&2
+}
+
+have_root()
+{
+    [ "$(id -u)" = 0 ]
+}
+
+main()
+{
+    have_root || error "you are not root"
+    [ $# = 0 ] && usage 0
+
+    iso_file=$1
+    shift
+
+    iso_file_clone=${iso_file}.clone.tmp
+    mountpoint=${iso_file%.iso}.mnt.tmp
+
+    [ -f "$iso_file" ]                                || error "not a file: $iso_file"
+    [ ! -f "$iso_file_clone" ]                        || error "refusing to clobber existing file: $iso_file_clone"
+    [ -d "$mountpoint" ] || mkdir "$mountpoint"       || error "could not create directory $mountpoint"
+    ! mountpoint -q "$mountpoint"                     || error "directory is already a mountpoint: $mountpoint"
+
+    cp --reflink=always "$iso_file" "$iso_file_clone" || error "cp failed"
+    trap 'rm -f "$iso_file_clone"' EXIT
+    btrfstune -f -S 0 "$iso_file_clone" 2>/dev/null   || error "btrfstune failed"
+    mount -o rw,loop "$iso_file_clone" "$mountpoint"  || error "failed to mount $iso_file"
+
+    chroot "$mountpoint" "$@"
+    result=$?
+    umount "$mountpoint" || warning "umount $mountpoint failed!  You had better do something about it"
+    rmdir "$mountpoint"
+    if [ "$result" = 0 ]; then
+        btrfstune -S 1 "$iso_file_clone" || error "btrfstune failed.  The original ISO is unmodified."
+        mv "$iso_file_clone" "$iso_file"
+    else
+        warning "The command executed within the chroot failed.  The original ISO is unmodified."
+        rm "$iso_file_clone"
+    fi
+}
+
+main "$@"