Re: vnd.c 1.254

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Sun, 17 Jan 2016 23:26:35 +0100
    From:        Michael van Elst <mlelstv%serpens.de@localhost>
    Message-ID:  <20160117222634.GA5226%serpens.de@localhost>

  | I'd rather have something that lists existing devices, allocates
  | a fresh one and tells me the name and works for all such pseudo disks.

I use the following script.   You will probably want to remove the
"echo cgd0" bit - I do that to permanently reserve cgd0 from this kind
of use (all my systems use that one for one particular purpose.)

I call it next_avail - usage is something like

	VND=$( next_avail vnd )
	CGD=$( next_avail cgd )
	
(and whatever else is similar, I know there is at least one more, but I
have forgotten which it is .. oh yes, raid of course...)

kre

#! /bin/sh

# Usage: next_avail cloner-type-disk
#	eg; next_avail vnd
#			(or cgd or raid ...)

next_avail ()
{
	local dev="$1"
	local N=$(( ${#dev} + 1 ))
	local unit units

	units=$(
		( sysctl -n hw.disknames ; echo cgd0 )	|
			tr ' ' '\012'			|
			grep '^'"${dev}"'[0-9]'		|
			sort -u -n -k 1.$N			)

	test -z "${units}" && {
		test -e "/dev/${dev}0a" || {
			echo >&2 "No ${dev}s available!"
			return 1
		}
		echo "${dev}0"
		return
	}

	N=0
	for unit in ${units}
	do
		if [ "${unit}" = "${dev}${N}" ]
		then
			N=$(( N + 1 ))
		else
			echo "${dev}${N}"
			return
		fi
	done

	test -e /dev/"${dev}${N}a" || {
		echo >&2 "All ${dev}s in use"
		return 1
	}

	echo "${dev}${N}"
}


for A
do
	next_avail "${A}"
done