lvm2/test/mkdtemp

#!/bin/sh
# Create a temporary directory, sort of like mktemp -d does.
# Usage: mkdtemp /tmp phoey.XXXXXXXXXX

# First, try to use the mktemp program.
# Failing that, we'll roll our own mktemp-like function:
#  - try to get random bytes from /dev/urandom
#  - failing that, generate output from a combination of quickly-varying
#      sources and gzip.  Ignore non-varying gzip header, and extract
#      "random" bits from there.
#  - given those bits, map to file-name bytes using tr, and try to create
#      the desired directory.
#  - make only $MAX_TRIES attempts

ME=$(basename "$0")
die() { echo >&2 "$ME: $@"; exit 1; }

MAX_TRIES=4

rand_bytes()
{
  n=$1

  chars=abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789

  dev_rand=/dev/urandom
  if test -r "$dev_rand"; then
    # Note: 256-length($chars) == 194; 3 copies of $chars is 186 + 8 = 194.
    head -c$n "$dev_rand" | tr -c $chars 01234567$chars$chars$chars
    return
  fi

  cmds='date; date +%N; free; who -a; w; ps auxww; ps ef; netstat -n'
  data=$( (eval "$cmds") 2>&1 | gzip )

  n_plus_50=$(expr $n + 50)

  # Ensure that $data has length at least 50+$n
  while :; do
    len=$(echo "$data"|wc -c)
    test $n_plus_50 -le $len && break;
    data=$( (echo "$data"; eval "$cmds") 2>&1 | gzip )
  done

  echo "$data" \
    | dd bs=1 skip=50 count=$n 2>/dev/null \
    | tr -c $chars 01234567$chars$chars$chars
}

mkdtemp()
{
  case $# in
  2);;
  *) die "Usage: $ME DIR TEMPLATE";;
  esac

  destdir=$1
  template=$2

  case $template in
  *XXXX) ;;
  *) die "invalid template: $template (must have a suffix of at least 4 X's)";;
  esac

  fail=0

  # First, try to use mktemp.
  d=$(env -u TMPDIR mktemp -d -t -p "$destdir" "$template" 2>/dev/null) \
    || fail=1

  # The resulting name must be in the specified directory.
  case $d in "$destdir"*);; *) fail=1;; esac

  # It must have created the directory.
  test -d "$d" || fail=1

  # It must have 0700 permissions.
  perms=$(ls -dgo "$d" 2>/dev/null) || fail=1
  case $perms in drwx------*) ;; *) fail=1;; esac

  test $fail = 0 && {
    echo "$d"
    return
  }

  # If we reach this point, we'll have to create a directory manually.

  # Get a copy of the template without its suffix of X's.
  base_template=$(echo "$template"|sed 's/XX*$//')

  # Calculate how many X's we've just removed.
  nx=$(expr length "$template" - length "$base_template")

  err=
  i=1
  while :; do
    X=$(rand_bytes $nx)
    candidate_dir="$destdir/$base_template$X"
    err=$(mkdir -m 0700 "$candidate_dir" 2>&1) \
      && { echo "$candidate_dir"; return; }
    test $MAX_TRIES -le $i && break;
    i=$(expr $i + 1)
  done
  die "$err"
}

mkdtemp "$@"